NASA-CR-200651

STATE UNIVERSITY OF NEW YORK AT STONY BROOK

Stony Brook, New York, 11794

Final Report for:

Analysis of EUV Dayglow Spectra of Triton, Titan and Earth

NAGW-2483

Submitted to:

The Neptune Data Analysis Program

Solar System Exploration Division

Code EL

National Aeronautics and Space Administration Headquarters

Washington, D.C. 20546

by

Research Foundation of SUNY at Stony Brook

Stony Brook. NY 11794March. 1996

Principal Investigator: Jane L. Fox

https://ntrs.nasa.gov/search.jsp?R=19960016585 2020-07-02T08:03:21+00:00Z

This report consists of two parts and appendices. The two parts are drafts of papers

that are being prepared for publication with co-author Roger YeUe. These papers are on

the ionosphere of Titan and heating ef[iciencies in the Titan thermosphere. Appended to

the report are copies of chapters published or in press that relate to the subject of this

project, and the grant is acknowledged, where possible, in these manuscripts. They are

"Ion chemistry in atmospheric and astrophysical plasmas" by A. Dalgarno and J. L. Fox,

"Dissociative recombination in planetary ionospheres" by J. L. Fox, "Hydrocarbon ions

in the ionospheres of Titan and Jupiter" by J. L. Fox, and "Aeronomy" (chapter for the

Atomic and Molecular Physics Reference Book, AIP Press, 1996, edited by Gordon Drake)

by J. L. Fox.

In addition, two talks based on work supported by this grant were given at annu-

M meetings of the Division of Planetary Sciences of the American Astronomical Society:

"Heating efIiciencies in the Titan thermosphere" (J. L. Fox and R. V. Yelle) Palo Alto,

November, 1991; "A new model of the ionosphere of Titan" (J. L. Fox and R. V. Yelle),

Kona, October, 1995. Invited talks were also presented by J. L. Fox at the Second Interna-

tion Symposium on Dissociative Recombination ("Dissociative recombination in planetary

ionospheres") in St. Jacut, May, 1992, and at the Third Internation Symposium on Dis-

sociative Recombination ("Hydrocarbon ions in the ionospheres of Jupiter and Titan") in

Ein Gedi, May, 1995. The subject matter of these talks included discussion of the Titan

ionosphere based on work supported by this grant.

Heating Efficienciesin the Thermosphereof Titan

J. L. FoxState University of New York at Stony Brook

R. V. YeUeBoston University

Abstract

We have constructed a coupled ion and neutral chemical model of the ionosphere

and thermosphere of Titan. Along with density profiles of ions and minor neutrals, we

have computed the heating rates and heating efficiencies for the neutrals and chemical

heating rates and efflciencies for the ions. We find that the neutral heating efficiency inour standard model varies from about 30% near 800 km to 22% near 2000 km. The most

important heating processes are neutral-neutral reactions and photodissociation. The ion

chemical heating rates maximize at about 10 eV cm-3s -1, and the corresponding ion

heating efficiencies peak near 1000 km at about 0.6%.

Introduction

The heating efficiency is the fraction of solar energy absorbed that is deposited locally as

heat. The EUV (4100-1000 ._.) and FUV (---1000-2000/k) regions of the solar spectrum

are absorbed in the thermospheres of planets. Solar energy is transformed to heat in pho-

todissociation and photoelectron impact dissociation of molecules, in exothermic reactions,

including ion-molecule reactions, neutral-neutral reactions, and dissociative recombination

of ions with electrons. Neutral heating efficiencies are important in determining the neu-

tral temperature structure and thus the chemical structure of the thermosphere. Although

the main source of ion heating in non-auroral planetary ionospheres during the daytime is

Coulomb collisions with photoelectrons, ion-molecule reactions are a source of heat that

can be important in the region of the ion peak (l:{.ohrbaugh et ai., 1979; Cravens et al.,

1980).

We have modeled the thermosphere and ionosphere of Titan, with a view toward

determining the ionospheric structure, altitude profiles of minor neutral species, and the

EUV heating efficiencies. We have adopted the F79050N solar fluxes of Hinteregger ipri-

rate communication; see also Torr et al., 1979!, which is appropriate to a period of high

solar activity, such as that which prevailed at the time of the Voyager 1 encounter with

Saturn and Titan (1981). The solar zenith angle in our model is 60 °. Photoionization

and photodissociation are included for N2, CH4, C2H6, C_H4, C2H2, and H2, as well as

photoionization of H, N and C. In addition, photoionization of CH3 by Lvman alpha, and

photodissociation of HCN are also included. Electron impact excitation and ionization

are included for N:, CH4, H2._ H. C and N. The cross sections for photoionization and

dissociative photoionization of N_ from threshold to 116 Zk were taken from Samson et al.

!1987 I. The .N: electron impact cross sections are the same as those adopted by Fox and

Victor i1988i in their study of electron energy deposition in N2 gas. The cross sections for

photoionization of hydrocarbons, and electron impact on H2, H and CH4 are the same as

those compiled by Kim and Fox r1990 . The cross sections for photodissociation of HCN

were taken from Nuth and Gl_cker 1982 and Lee 119801. The cross sections for photoion-

ization of C and N were taken from LeDourneuf et al. I1976], Cantu et al.. 1981i, and

Daltabuit and Cox r19721. The electron impact ionization cross sections for C and N were

adopted from the measurements of Brook et al. 11978]. The ionization potential of CH3 is

9.84 eV, and photoionization by solar Lvman alpha is possible, but the cross section has

not been computed or measured. We assume, as did Strobel [1975!, that the cross section

is equal to that of atomic carbon at threshold. 1.2 × 10 -17 cm 2.

2

Sources of Heating

Photodiasociation. In photodissociation, the amount of energy that goes into kinetic energy

is the difference between the energy of the photon and the dissociation energy (which may

include some internal excitation of the fragments). In the absence of information about

the electronic states of the fragments, they are assumed to be produced in their ground

states. When there are molecular products, some of the energy may be taken up as

vibrational energy of the fragments. The energy that appears as vibrational excitation in

photodissociation has been found to be small [cf. Fox, 1988 and references thereini; this

would be expected to be especially true when the fragments are H atoms. We assume here

that 25% of the excess energy appears as vibrational energy of molecular products, and

the remainder is converted to kinetic energy, as we have in previous calculations of heating

efficiencies ie.g. Fox, 1988]. A half-collision model (Holdy et al., 1970) suggests, however,

that when one of the fragments is very fight, such as a hydrogen atom or molecule, the

energy that appears as vibrational excitation of the other fragment may be very small.

It is possible that only 10-15% of the energy is taken up as vibrational excitation in

photodissociation.

The N2 dissociation threshold is large, about 9.76 eV, and because most of the dissoci-

ation occurs through discrete excitation into predissociating states in the singlet manifold,

the effective dissociation threshold is larger. Consequently, N2 does not absorb longward of

about 985 J_. Although N, is the major species in the atmosphere, the peak heating rate due

to photodissociation of N2 is only 5.7 eVcm-as -: at about 1060 kin. near the ionospheric

peak. By contrast. CH4 is a strong absorber, and photodissociation of CH4 is the most

important heating process of this type. The peak heating rate is about 1.4 × 10aeVcm-as -1

at 770 km. Although at this altitude infrared heating may be more important than solar

ultraviolet heating, the dominance of heating due to methane photodissociation extends

to higher altitudes. At 1060 km. the heating rate due to methane photodissociation is

1.23 _'<102 eVcm-as -I Even HCN photodissociation is more important than that of N,,

with a heating rate of about 8 eVcm-as -I at 1060 kin.

Chemical reactiona. The energy released in exothermic reactions can appear as ki-

netic energy of the products, thus resulting in heating. The partitioning of kinetic energy

between the products in any reaction is determined by conservation of momentum and

energy. For the case in which there are only two products, the kinetic energies of species

1 and 2, el and e2, respectively, are given bv

el = m=/(rnl - rn2)e

and

= ml/(ml--m2)

where mj is the mass of species j and e is the total kinetic energy released in the reaction.Dissociative recombination reactions in particular are often very exothermic and con-

tribute significantly to neutral heating. On Mars and Venus, dissociative recombination

of the major ion, O_, is the most important chemical heat source for the neutrals [Fox

and Dalgarno, 1979, 1981; Fox, 1988]. On the Earth, dissociative recombination of NO*

is the most important heat source among reactions of species in their ground states [Tort

et al., 1980]. On Titan, we find that dissociative recombination is not as important as it

3

is on the terrestrial planets, partly because the ions are "processed" more, that is, they

have undergone more transformations before they recombine. More important, however, is

the presence of methane, which is a strong absorber, increasing both the heating rate due

to photodissociation and the production rate of neutral fragments that can participate in

neutral-neutral reactions compared to the terrestrial planets.

Dissociative Recombination. In dissociative recombination of polyatomic molecular

ions, as in photodissociation, some uncertainty exists about how much of the exothermicity

appears as vibrational excitation of the molecular products. And just as for photodisso-

ciation, a half-collision model suggests that little energy is expected to be deposited as

vibrational excitation. We have assumed that 25% of the energy released appears as vi-

brational energy of molecular fragments; that value may be an overestimate where one of

the products is an H atom. For example, an important dissociative recombination reaction

for neutral heating is that of HCNH +. There are four exothermic product channels for

this reaction:HCNH + + e _ HCN + H

---, HNC + H

The only information that is available about the product channels is the measurement of

Adams et al. 11991!, that indicated that 0.63 H atoms are produced per recombination.

This impfies that the sum of the branching ratios for the first two channels is 63% and

the sum of the second two branching ratios is 37%. We somewhat arbitrarily assume that

production of HCN, the more stable isomer, is the dominant channel of the first two. and

that the third channel is more important than the fourth.

Electron impact heating. In electron impact dissociation some of the energy lost bv the

electron may appear as kinetic energy of the neutrals produced. In general, the fraction

of energy that appears as kinetic energy is not fixed for a given process and it is therefore

not possible to determine the heating due to electron impact dissociation exactly. An

average value may be determined from time-of-flight studies, or derived from electron

energy loss spectroscopy, but measurements are not available for all of the electron impact

dissociations. Fortunately, Prokop and Zipf F19821 have measured the average kinetic

energy of the N atoms that are released in electron impact dissociation and dissociative

ionization of Nz, and report values of 0.45 eV and 3.0 eV, respectively. Since this is the

most important species in the Titan atmosphere, it accounts for most of the photoelectron

energy loss at the ion peak, near 1000 km. In computing the heating due to electron

impact dissociation, we have adopted the measured values for N2, and we have assumed a

value of 1.0 eV per dissociation or dissociative ionization of H2 and CH4.

Ion-molecule reactionn. In ion-molecule and neutral-neutral reactions, the exother-

micity can appear as internal energy of the products, as well as kinetic energy. In general,

little information is available about the partitioning of energy among the various modes.

For our standard calculation, we have assumed that 60% of the energy appears as vibra-

tional energy of the products. We also then compute lower and upper limits to the heating

efficiency using the values 80 and 40%, respectively. As mentioned above, for ion-molecules

reactions, the partitioning of kinetic energy between the the neutral and the ion product

is determined by momentum conservation. The most important ion-molecule reactions for

thermospheric heating are

N_-CH4 _CH_--N:-H

and

CH_-, CH4 ---* CeH_- -- H_.

The most important neutral-neutral reactions are:

CH2 CH2 _ C2H_ +H2

and

NH + N ---, N2 -" H.

Results

The neutral heating rates as a function of altitude are presented in Figure 1 and resulting

heating efficiencies are shown in Figure 2. The standard values vary from about 0.30 at

800 km to 0.22 at 2000 km. The lower and upper limits are smaller and larger bv about

0.05 near 800 km but converge to nearly the standard value at 2000 kin. These heating

efficiencies are very different from those appropriate to Earth, which are in excess of 0.50.

and are more like those for Venus and Mars, which are about 0.20-0.24 It is apparent that

in N2 atmospheres, it is the minor species that dominate the absorption and heating: 02

for the terrestrial case. and methane for Titan.

The ion chemical heating rates are shown in Figure 3 for the standard, upper and

lower limit models and and _he corresponding heating efficiencies are shown in Figure 4.

The chemical heating rates are much smaller than the neutral heating rates, and attain

maximum values on the order of 10 eVcm-as -1 near the ion peak. The heating efficiencies

maximize near the ion peak at values of 0.003, 0.006, and 0.009 for the lower limit, stan-

dard, and upper limit models. Vfe can compare the ion chemical heating rates to those

computed by Roboz and Nagy (1994). Their %olaf-only" heating rates maximize near

the ion peak with values that are much less than ours. about 0.3 eVcm-as -1. The source

of the difference is uncertain, but probably arises from our use of a more complete set of

reactions.

References

Adams, N. G., C. R. Herd. M. Geoghegan, D. Smith, A. Canosa, J. C. Gomet, B. R.

Rowe, J. L. Queffelec, and M. Morlals, Laser induced fluorescence and vacuum ultraviolet

spectroscopic studies of H-atom production in the dissociative recombination of some

protonated ions, J. Chem. Phys., .¢85_, 1991.

Brook, E., M. F. A. Harrison and A. C. H. Smith, J. Phys. B, 11, 3115. 1978.

Cantu, A. M. *I. Mazzoni. M Pettini, and G. D. Tozzi, Phys. Rev. A.. 23. 1223, 1976.

Daltabuit, E.. and D. P. Cox. Astrophys. Y., 177, 855, 1972.

Fox, J. L., Planet. Space Sci.. 36, 37, 1988.

Fox, J. L. and A. Dalgarno, Planet. Space Sci., 27, 491, 1979.

Fox, J. L., and A. Dalgarno. J. Geophys. Re_. 8_, 7315, 1979.

Fox, J. L., and A. Dalgarno, J. Geophys. Res., 86, 629-639, 1981.

Fox, J. L., and G. A. Victor, Planet. Space Sci., 36, 329, 1988.

Holdy, K. E., L. C. Klotz and K. R. Wilson, Molecular dynamics of photodissociation:

quasi-diatomic model for ICN. J. Chem. Phys. 52, 4588, 1970.

James, G., J. AjeUo, B. Franklin, and D. Shemansky, 3". Phys. B: At. Mol. Phys., 23,

2055, 1990.

Kim, Y. H., and J. L. Fox, Geophys. Res. Left., 18, 123, 1990.

LeDourneuf, M., Vo Ky Lan, A. Hibbert, J. Phys. B., 9, L39, 1976.

Lee, 3.. Chem. Phys., 72, 6414. 1980.

Nuth, and Glicker, 3.. Quant Spectrosc. Rad. Transl., 28, 223, 1982.

Prokop, T. M., and E. C. Zipf, EOS (Trans. Am. Geophys. Union), 63. 393, 1982.

Roboz, A. and A. F. Nagy, The energetics of Titan's ionosphere, J. Geophys. Re_., 99,

2087-2093, 1994.

Rohrbaugh, R. P., J. S. Nisbet. E. Bleuler. and J. R. Herman, The e_ect of energetically

produced O_ on the ion temperatures of the Martian thermosphere. Y. Geophys. Res..

8,_, 3327. 1979.

Samson, J. A. R.. T. Masuoka. P. N. Pareek. and G. C. Angel. Y. Chem. Phys.. 86. 6128,

1987.

Strobel. D. F.. Discussion of paper by S. S. Prasad. and A. Tan, "The Jovian ionosphere".

Geophy_. Re_. Lett.. 2. 521. 1975.

Torr, D. G.. et al.. Geophys. Res. Lett., 6. 771. 1979.

Torr, Xl. R., P. G. Richards. and D. G. Torr. J. Geophys. Res., 85, 6819. 1980.

Figure 1. Altitude profiles of the heating rates of the most important processes in the

Titan thermosphere.

Figure 2. Altitude profiles for the heating efficiencies for solar radiation in the 14-2000A

interval. The standard, upper limit and lower Limit profiles are illustrated.

Figure 3. Altitude profiles of the ion chemical heating rates in the Titan thermosphere

for the standard (solid curve), lower limit (short-dashed) and upper limit (long-dashed)

models.

Figure 4. Altitude profiles for the ion heating efficiencies for solar radiation in the 14-

2000_ interval. The standard (solid curve), upper Limit (short-dashed) and lower limit

(long-dashed) models are illustrated.

7

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DRAFT

A New Model of the Ionosphere of Titan

J. L. Fox

State University of New York at Stony Brook

R. V. Yelle

Boston University

Abstract

We have constructed a new model of the ionosphereof Titan that includes 69 speciesand

626 reactions. Although N_- is the major ion produced in the ionosphere, the ionizationflows to ions whoseparent neutrals have lower ionization potentials and to specieswith

large proton affinities. In contrast to other models, which have predicted that HCNH-should be the major ion, wesuggestthat the major ions at and below the ion peak near1050 km are hydrocarbon ions and H, C, and N-containing ions. Our predicted peakelectron density for a solar zenith angleof 60° is 6.3 × 10acm-3 at an altitude of 1050km.

Introduction

In addition to N2 and CH4, the thermosphere of Titan contains significant densities of H_,

H, and non-methane hydrocarbons such as acetylene, ethane, and ethylene (e.g., Hunten

et al., 1984, Strobel et al., 1992), and appears to be well-mixed to very high altitudes. The

atmosphere may also contain as much as 14°/0 Ar. The homopause in the model of Strobel

is near 1050 km, where the eddy diffusion coefficient is about 1 × 109 cm _ s -1. The exobase

is near 1500 km. and the density profiles of l=i and H_ are altered appreciably by thermal

escape at the top of the atmosphere.

Information about Titan's ionosphere is Limited to the radio occultation measurements

made by the \'oyager t spacecrah. Lindal et al. (1983) reported only upper Limits of

(3 - 5) × 10 a cm -3 near the terminators as the spacecraft entered and e_ted the occultation

region. Recently, Bird et al. (1995) have reanaivzed the Voyager radio occultation data

and reported a possible detection with a peak electron density of 2700 cm -3 at an altitude

of 1190 km near _he evening terminator.

The ionosphere of Titan has been predicted to arise from both solar photoionization

and from the interaction of the neutral atmosphere with energetic electrons from Saturn's

magnetosphere, in which the orbit of Titan is embedded during part of its orbit (e.g.,

Strobel and Shemansky, 1983: Atreya, 1986). Strobel et al. (1991) found, however, that the

N + 1085 ._ and .N_ Lyman-Birge-Hopfield band intensities that were measured by Voyager

1 spacecraft during its Titan flyby in 1980 could be reproduced with the solar source alone.

Cravens and co-workers [Keller et al., 1992; Gan et al., 1992] constructed a model of the

ionosphere of Titan that included the interaction of energetic magnetospheric electrons

with the thermosphere and found it to be a minor source. We model here the ionosphere of

Titan produced by photoionization and photoelectron-impact ionization alone. Although

we ignore here the interaction of the thermosphere with Saturn's magnetosphere, we do

not mean to imply that magnetospheric electrons are unimportant all the time or for every

process. In all probability, however, they are unimportant for ion production near and for

a substantial distance above the ion peak.

2

The Model

The background model neutral thermosphere that we have adopted here is shown in Fig.

1. The density profiles of N2 and CH_ are taken from $trobel et al. (1992), and mixing

ratios of C2H2, C2H4, C2H6, and C4H2 are taken from Yung et al. (1984). The mixing

ratio of methane has been estimated as 2-10% in the Titan atmosphere (Hunten et al..

1984), but we have adopted a mixing ratio of 3% at the lower boundary, consistent with

the preferred model of Strobel et al. (1992). The CO mixing ratio is adopted from the

ground-based measurements of Gurwell and Muhleman (1995). The temperature profile is

taken from Strobel et al. (1992), and is nearly isothermal at the exospheric temperature

of approximately 175K above about 1000 km. The electron temperatures are taken from

Gan et al. (1992).

In our model, the density profiles of six species were fixed, and we compute the densi-

ties of 34 neutral species and 35 ions, which are enumerated in Table 1. We have included

photoabsorption and photoionization of N2, CH4, C2H2, C2H4, C2H6, N, C, tt and H2, pho-

todissociation of HCN, and photoionization of CH3 by Lyman alpha. The solar spectrum

used is the high solar activity F79050N spectrum of Hinteregger (private communication:

see also Torr et al.. 1979), and the solar zenith angle is 60 °. Photoelectron-impact ion-

ization was included for N__, CH4. H. H2, N and C. The most important production rate

profiles are shown in Fig. 2. The major ion produced is N_- from 600 to 1800 km. and

CH_- above that altitude. Other important ions produced include N-. CH3, C2H.:-. and

C_H_-.

The ion density profiles were computed including 626 chemical reactions. The ion-

molecule, neutral-neutral and dissociative recombination reactions in the model are listed in

Table 2 along with their assumed rate coefficients. Most of the rate coefficients for the ion-

molecule reactions were taken from the compilations of knicich and Huntress (1986) and

knicich (1993). For neutral-neutral reactions, rate coefficients were taken from the model of

Yung et al. (1984) and from models of the interstellar medium (e.g., MiUar et al., 1988). For

many of the most important dissociative recombination coefficients, the rates are unknown;

where no measurements are available, values of (3- 3.5) .'< 10-7(300/T_)'}5 cm 3 s-1 were

assumed. Even where dissociative recombination coefficients have been measured, in many

cases there is little information about the product yields, for which in general there are

many possibilities, especially for polyatomic ions. Because the ion and neutral chemistries

are coupled, (and because the exothermicity and production of fast atoms depend on the

channel by which the recombination proceeds), measurements of the product yields are

important. Here we have assumed that the available channels are populated with equal

probability. Eddy and molecular diffusion for neutrals, and ambipolar diffusion of ions

were included in our model, for which the lower and upper boundaries were at 600 km and

3000 km, respectively.

3

The predicted densitiesof the major ions are shown in Fig. 3. The peak electrondensity is about 6.3 x 10acm-a near 1050 km. This is larger than either the Voyagerupper Limits and the possibledetectionof Bird et al. (1995), but thosemeasurementsarefor the terminator region. We would expect the densities to be substantially larger thanours, which are for the davsideat 60° solar zenith angle.

Although N_- is the major ion produced up to about 1800km, below about 1900kmit is lost by reaction with methane

N_-- Ctt4 ---, CH_- + N2 + H2

CH3 + N2 + H,

(la)

(lb)

and above that altitude by the reaction:

N_- H_ _ N_H + + H. (2)

Reaction with H and charge transfer to acetylene are minor loss processes in the lower iono-

sphere. Dissociative recombination becomes the second most important loss mechanism

above about 2500 km. Altitude profiles for the loss processes are shown in Fig. 4.

The major ion at high altitudes is N_H +. The major production and loss mechanisms

for N2H'- are shown in Fig. 5. N oH- is produced mainly in the reaction of N_ with H2

(reaction 2) below 1300 km and above 1700 km. Over a limited altitude range, about

1300-1700 km. the most important source is

H2 - N2 _ N:H"- -- H (3)

Other minor sources include the reactions of H_- with N2 and NH'- with N2. The most

important loss mechanism is dissociative recombination

N2H + - e _ products (4)

above 2300 km and proton transfer to CH4:

N2 H- --CH4 --*CH + + N2 (5)

below that altitude. Reaction with C2H2:

N_H- + C2H2 --*C2H + + N2 (6)

is also significant near the ion peak.

In the altitude region from 1300-1800 km, the major ion is C2H_-. At the peak near

1050 km the dominant ion is the pseudo-ion C,H_-. The density of C4H_- exceeds that of

C,H + near its peak at about 750 km. Most other models have predicted that HCNH ÷

would be the major ion (Ip, 1990; Keller et al., 1992; Keller and Cravens, 1994). The

major production and loss mechanisms for HCNH + in our model are shown in Fig. 6.

Above about 1050 km, HCNH + is produced in the reaction:

N + : CH4 -- HCNH ÷ + H2.

Below the ion peak the most important source is proton transfer from C2H_- to HCN:

C2H_- - HCN ---, HCNH + + C2H4.

(7)

Minor sources include the reactions of HCN ÷ with CH4 at high altitudes and proton

transfer of C2H_- to I:tCN at low altitudes. Below the ion peak, HCNH- is lost mainly by

proton transfer to C4H2:

HCNH ÷ : C4H2 ---' C_H_- + HCN. (10)

The proton transfer reactions with HC3N, and with NH3 are also significant below about

1000 km. Loss is by dissociative recombination above that altitude.

The major production reactions for C,H:_ are reactions of C1- and Ce- hydrocarbon

ions with acetylene, C2- hydrocarbon ions _fith methane and a few reactions of C1- or C2-

hydrocarbon ions with ethvtene and ethane. The most important production reactions are

plotted in Fig. 7 and are listed below:

CH[ - C._H2 -- C3H_ - He

CeH_- - C2H2 -- C3H_- + CH3

C2H? - C2H2 -- C4H + + H

C2H_ - C2H: -- C3H_ + CH4

C2H_- - Cell2 -- C4H +

C2H.: - CH_ _ C3HI

C2H_- , CH4 -" C3H +

C2H? + C2H4 -_ C3H_-

C2H5+ _-C2H_ -_C3H[

CH_" - C2H6 -_ C3H_

Although C_H_" clearly does not represent a single

in that sense, the computed peak density of HCNH + is

than the total electron density.

(10)

(11)

(12)

(13)

+He (14)

÷H (15)

+H2 (16)

+ CH3 (17)

+ CH4 (18)

+H2 (19)

ion, and thus is not the major ion

almost an order of magnitude less

(8)

Photoelectron fluxes

A secondary but important source of ions near and below the ion peak is photoelectron

impact ionization. The predicted primary and steady-state fluxes from of photoelectrons 0

to 200 eV at 0.5 eV resolution near 1000 km are shown in Fig. 8. The top spectrum is the

initial spectrum and the bottom is the steady-state spectrum averaged over three intervals

(1.5 eV). The spectrum displays a sharp drop-off above 70 eV, where photoelectrons pro-

duced by the the last of the strong solar lines appear. The spectrum appears similar to

that of Gan et al. (1992) for their solar-only case, but the sharp bite-out from about 20 to

40 eV does not appear in our spectrum. The reason is unknown, but will be investigated.

Discussion

Solar ionizing photons are absorbed in the thermospheres of planets and satellites, and the

peak ionization rate is usually found at a column density of about 1017 cm -2. This altitude

may be near or above the homopause, where the transition from transport by large scale

mixing to that by molecular diffusion takes place. Although the density of CH4 eventually

exceeds that of N2 at high altitudes on Titan, the ionization peak appears roughly at the

homopause, which is near t050 km in the Strobel (1992) model. There the major neutral

species is N__ and the mixing ratio of CH4 is about 3%. Although hydrocarbon and related

ions clearly comprise only a small fraction of the ions produced by photoionization and

electron-impact ionization on Titan. our model shows that such ions mav be abundant

near and below the major ion peak.

The major ions produced in any ionosphere will be transformed by ion-neutral re-

actions if they are formed in the presence of sufficient densities of neutrals with which

they can react. In reducing environments, such as the atmospheres of the outer planets

and their satellites, ionization tends to flow from species whose parent neutrals have small

proton affinities to species whose parent neutrals have large proton affinities. On the giant

planets, the terminal ions will be large protonated hydrocarbons (e.g., Kim and Fox. 1991;

1994); on Titan. the major species will be hydrocarbon ions, protonated nitriles and other

ion containing C. It and N. In most cases, the available information about ion chemistry

is insufficient to identify the terminal ions in the bottomside ionospheres, but since larger

molecules tend to have larger proton affinities, the average size of the ion probably increas-

es with decreasing altitude. In order to improve our understanding of these ionospheres,

rate coefficients and branching ratios for reactions of hydrocarbons and hydrocarbon ions,

and neutral and ionic species containing C, tt and N are needed, including those for disso-

ciative recombination reactions. Some representative proton affinities are shown in Table

3.

Clearly, a major uncertainty in the ionosphere model is the accuracy of the neutral

model, including the density profiles computed by Yung et al. (1984). We note here that

the crucial C4H2 density was underestimated in the middle atmosphere in the Yung et

al. model compared to measured values. It seems that, if anything, the actual values

will be larger than those we have assumed. Moreover, the conclusion that HCNH t does

not dominate the ion density profile depends only on the presence (with a large enough

density) of some species that has a higher proton affinity than HNC or HCN, or of some

other chemical pathway to the protonated species. With a fairly large thermospheric

mixing ratio of methane, and the presence of solar ultraviolet photons, that is all but

certain.

Acknowledgement, This work has been partially supported by grants NAGW-2958,

and NAGW-2483 to the State University of New York at Stony Brook.

References

Anicich, V. G. and W. T. Huntress, Astrophys. J. Suppl. Set., 62 553, 1986.

Anicich, V. G., Evaluated bimolecular ion-molecule gas phase kinetics of positive ions for

use in modeling the chemistry of planetary atmospheres, cometary comae, and interstel-

lar clouds, Astrophys. J. Suppl., 84, 215, 1993.

Atreya, S. K., Atmospheres and Ionospheres of the Outer Planets and their Satellites,

(Springer Verlag, New York, 1986).

Bird, M. K., R. Dutta-Roy, S. W. Asmar, and T. A. Rebold, Possible detection of Titan's

ionosphere from Voyager 1 radio occultation observations, Preprint, October, 1995.

Gan, L., C. N. Keller, and T. E. Cravens, Electrons in the ionosphere of Titan, J. Geophys.

Res., 97, 12,137-12,151, 1992.

Gurwell, M. A., and D. O. Muhleman, Icarus 117 375, 1995.

Hunten, D. M., M. G. Tomasko, F. M. Flasar, R. E. Samuelson, D. F. Strobel, and D. J.

Stevenson, in Saturn, University of Arizona Press, Tucson (1984), pp. 671-759.

Ip, W.-H., Titan's upper ionosphere, Astrophys. J. 362, 354, 1990.

Keller, C. N., T. E. Cravens. and L. Gan, A model of the ionosphere of Titan, J. Geophys.

Res., 97 12,117-12,135, 1992.

Keller, C. N. and T. E. Cravens. One-dimensional multispecies hydrodynamic models of

the wakeside ionosphere of Titan. J. Geophys. Res., 99, 6527-6536, 1994.

Kim, Y. H., and J. L. Fox. The Jovian ionospheric E-region, Geophys. Res. Lett., 18. 123.

1991.

Kim, Y. H., and J. L. Fox. The chemistry of hydrocarbon ions in th Jovian ionosphere.

Icarus, 112. 310, 1994.

Lindal, G. F., G. E. Wood. H. B. Hotz, and D. N. Sweetnam, The atmosphere of Titan:

An analysis of the Voyager 1 radio occultation measurements, Icarus. 53, 348, 1983.

Millar, T. J., D. J. DeFrees. A. D. McLean, and E. Herbst, Astron. Astrophys. 194 250,

1988.

Strobet, D. F., and D. E. Shemansky, EUV Emission from Titan's upper atmosphere:

Voyager 1 encounter, J. Geophys. Res., 87, 1361-1368, 1982.

Strobel, D. F., R. R. Meier. M. E. Summers, and D. J. Strickland, Nitrogen airglow sources:

Comparison of Triton, Titan and Earth, Geophys. Res. Lett. 18, 689-692, 1991.

Strobel D. F., M. Summers. and X. Zhu, Titan's upper atmosphere: Structure and ultra-

violet emissions, Icarus, 100, 512, 1992.

Torr, D. G., M. R. Torr, R..3,. Ong and H. A. Hinteregger, Ionization frequencies for major

thermospheric constituents as a function of solar cycle 21, Geophys. Res. Left. 6, 771,

1979.

Yung, Y. L., M. Allen, and J. P. Pinto, Photochemistry of the atmosphere of Titan:

Comparison between model and observations, Ap. J. Suppl. Set., 55, 465, 1984.

Figure Captions

Fig. 1. Neutral density profiles in the thermosphere of Titan that were adopted in these

calculations. The densities of N,, CH4, C2H2, C2H4, C2H6, and CO were assumed to be

fixed. The density profiles of H2 and H were computed self-consistently in the model.

Fig. 2. The computed production rate profiles for the most important ions produced in

the Titan ionosphere.

Fig. 3. Computed steady-state densities of the most important ions produced. The solid

curves are labeled by the ion produced dashed and the dashed curve is the electron

density profile. C,H + is a pseudo-ion that represents all hydrocarbon other than those

included explicitly.

Fig. 4. Altitude profiles of the major loss processes for N + in the Titan ionosphere. The

curves are labeled by the species with which the N + ions react.

Fig. 5. Altitude profiles for the major sources (top) and sinks (bottom) of N2H + in the

Titan ionosphere.

Fig. 6. Altitude profiles for the major sources (top) and sinks (bottom) of HCNIt + in the

Titan ionosphere.

Fig. 7. Altitude profiles of the major sources of C_H] in the Titan ionosphere.

Fig. 8. Computed primary (top curve) and steady-state (bottom curve) photoelectron

fluxes at 1050 km. The bin size for the primary fluxes is 0.5 eV. The steady-state fluxes

have been averaged over three bins. The peak at 200 eV is an artifact that results

from the treatment of photoelectrons with energies larger than 200 eV. which have been

divided into one or more 200 eV electrons and an electron with the remainder of the

energy.

+_+,_+ +_+a- +_+_ + +

+ _ + _ ___,'-_-_4_4_a,+a-+_+e_ 4 ++ _ +

0

0

÷(_

t_

("1)

n.

_°

0

"_ 1_... _'Q. Reactions in the Titan Model

Reaction Rate Coefficient

H++ CH4---* CH_-- I-I.o,- 3.690 x 10 .9

H*+ CH4---_ CH_'+ H - 8.100 x 10 -9

H++ C2Hs--_ C2H_+ H2- H., 1.300 x 10 -_

H++ C_H6---* C_.H_-+ H._,-- H 1.300 x 10 -_

H*+ C_H6--_ C2H_-+ H_- 1.300 x 10 -_H'-+ HCN --_ HCN_-+ H - 1.100 x 10 .5

H++ NH3--_ NH_+ H + 5.200 x 10 .9H++ NH --, NH +_- H _- 2.100 x 10 -9

H++ H2-* H++ - 3.200 x 10-29(T,/'300]°'°°exp(-0.00/T,) [,M)

H++ C_.H2--* C2H++ H_+ 4.300 x 10 -9

H_+ CH4--, CH_+ H2.-r H 2.280 x I0 -v

H_+ CH4--* CH_+ H._,- 1.410 x 10 -_

H_+ CH4---* CH_-+ H - 1.140 × 10 -10

H_+ C2H2---' C2H_+ H2-r 4.820 x 10 -9

H_+ C2H2---* C2H_'+ H + 4.770 x 10 -m

H.;-+ H2---, H_+ H - 2.080 × 10-9

H+T N2--" N2H++ H - 2.000 x 10 -9

H$+ C'2H4--* C2H++ H2_ 2.200 x 10 -9+ ,

H_ C2H4---, C_H 3 -- H2-,- H 1.810 x 10 -_

HZ-- C,eH4--* C2H_÷ H._- H._ 8.800 x 10 -w

Hi7= C._,H_---_ C,H_'_ H_- 2.940 × 10-_

Hi7- C2H(_---" C.,H_- H'2- H 1.370 :_ 10 -_

Hi7" C_H,--, C..,H_-- H2- Hu 2.350 x l0 -_

HT+ C.,H_---* C__H_- H_- H_ 6.860 × 10 -I'<'

HiT- C2H6---* C,H_- H,- H.., 1.960 x 10 -1''

H,7+ NH:_--* NH_- H..,- 5.700 _ I0 -_

HiT+ HCN ---* HCN*- H2- 2.700 x 10 -_

HiT-s- H ---* H +: H.,- 6.400 "< 10 -1_'

HY- N --, NH +: H - 1.900 × 10 -_*

Hj= NH --, NH-- H2- 7.600 × 10-l')

H,7- NH --* NHj- H - 7.600 × 10 -l"

H.]-_ CO --* HCO': H = 1.100 × 10 -_*

H_-- CH4--* CH_-- H_- 2.400 "< 10 -_

H:]-:- N._--_ N_.H _-- H'2_ 2.000 × 10 -_

H:]-- HCN _ Ho_CN +"- H_- 9.500 × 10 -9

H:_'+ C'.,H2--, C_H_+ H2- 2.900 × 10 -_

H_+ C_H4----* C.,H_-+ H2-r H.: 6.900 x 10 -l°

H_+ C.,H_---, _- ' .C_H 3 - H_+ H_ 1.610 x 10 -_

H_+ C._H6---* C2H_÷ H_+ 2.400 x 10 -')

H:[+ C._H6---* C2H++ H_+ 2.400 x 10 -_1

H++ N --*NH++ H_+ 2.600 × I0-_°

H++ N _ NH++ H + 3.900 x 10-_°

H_+ NHa--, NH_+ H_+ 9.100 x 10 -9

H_+ CHaCN--* +_-C_H_N: H_+ 7.300 × 10 -9

H2+ CO ---, HCO++ H_+ 1.700 x 10 -9

H_+ NH ---, NH_+ H._+ 1.300 × 10 -9

C++ CH4--" C2H.,*+ H_+ 4.480 x 10 -9

C++ CH4--* C2H_-+ H + 9.520 x i0-_°

C++ C_H2--" C_H++ H + 2.800 x I0-m

C+÷ C2H4--* C2H++ CH + 8.500 x 10 -It

C*+ C2H4-'*C._HT*C +C++ C'_,H4--_C,H_+ H__+C++ C,.H4--_C_H_+H +C++ C_H_--,C2H++CH4+C++ C2H6-_ C2H_+ CH3+

C++ C2H6--+ C_H_'+ CH +

C++ C2H6--_ C.H++ H2+ HC++ HCN --.C2N++ H _-

C*+ CH_NH2--* - C +

C++ CH_NH2--_ + CH +

C++ HC3N--_ C.H++ HCN -

C += HC3N--_ C.Hy++ CN +

C++ HC3N--_ C_HyN:++ H _-C++ HC3N---* C2N++ C2H+

C++ NH3---* NH++ C +

C*+ NH3--, H2CN++ H -4-

C++ NH3--. HCN++ H2+

C++ C2N2--* C_N++ CN +

C++ H2--* CH++ H +

C++ H2---* CH++ +

C++ H_-. CH++ +

C++ CH --.C +:- H +

C++ CHaCN--_ C_HyN..++ -

C÷+ NH -_ CN*= H -

CH +- H --*C*÷ H2+

CH+= H,:_ CHT_- H -

CH + -

CH*+

CH+=

CH +-

CH +-

CH+=

CH+=

CH++

CH + -

CH+- '

CH + -

CH++

CH+:

CH++

CH++

CH+-_

CH++

CH_+

CH++

CH_+

CH_+

CH+_-

CH++

CH_+

CH_+

CH++

CH_+

CH4-" C2H_" H2-- H

CH4-_ C'2H:T= H..,-

CH._--_ C_H T- H +

C_H_-_ C_H_+ H --N -_ CN +" H -

N -_ H + : CN -

NH:_--* H_CN*- H'2-

NH:{-_ NHI+ CH -

NH:{-_ NH?+ C +

HCN -_ H2CN +_- C -

HCN -_ C_N _-- H2±

HCN -_ C_HyN.++ H -

CH3NH_-_ C_H_N++ CH?-

CHaNH2-_ C_H_N++ CH -

CHaNH2--_ CzHyN- +_- C -CO _HCO++C +

NH --.CN++ H_.+

H2--.CH++ H +

CH4-_ C._H_+ H2+CH.,--_C2H_+ H +

C_.H2--.C_H++ H +

N --_ CN++ H2+

N --, HCN++ H +

NH3---, NH++ CH +

NHa-_ C_H_N++ H :

HCN -. C_HyN.++ H -

CH3NH=--* + CH3+

1.700 ×

3.400 x

1.020 ×

1.700 x

5.100 x

1.700 x

8.500 x

2.900 x

1.430 x

7.700 x

2.500 x3.250 x

1.400 x

1.000 x

5.290 x

1.560 x

2.070 x

1.900 x

1.200 ×

1.000 x

4.000 x

3.800 x5.600 x

7.800 x

7.500 x

1.200 x

1.430 x

1.090 ×

6.500 x

2.400 x

9.500 ×

9.500 ×

1.840 x

4.590 x

4.050 x

1.800 x

3.600 x

2.400 x

1.100 x

2.200 x

8.800 x

7.000 x

7.600 x

1.600 x

8.400 x

3.600 x

2.500 ×

1.100 x

1.100 x

5.310 ×

2.000 x

1.800 x

1.160 x

10- w

10- m

10 -9

1O- 1o

10-10

10-1o

10-1o

10 -9

10 -9

lO-m

I0- 1()

10 -9

10 -9

lO-tO

10-1o

lO-lO

10-Io

10 -9

10-16

10-15

10-16(T./300)- 2°°exp[ -O. O0/T. )10-1o

10 -9

10- m

10- m

10 -9

10- t')

i0-9

lO-tt

10-!_

10-_,_

10-9

10-m10- m

10-9

10- w

i0-Io

10 .9

lO-tO

10- m

lO-t2

lO-tO

10 -9

10-1o

10-1o

10-9

10-10

10-10

10-1o

10 -9

10 -9

10 -9

ca++CH+_-

CH++

CH++

CH++

CH_+CH_+

CH_+

CH_+

CH++

CH++

CH_+

CH_+

CH_-+

CHT+CH++

CH_+

CH++

CH++

CH++

CH++

CH_-

CH++CH_-CHT÷

CH T -

CH_ +CH,+ -

CHT:

CH +

CHT÷CHT+

CH_-

CHT+CHT.CHT-_

CHT+

CH_-+

CHT+

CHT±

CHT+

CHT+

CH++

CH++

CH++

CH++

CH++

CH_+

CH++

CH++

CH++

CHaNH2_ C_H,jN:-+ CH__-

CH:{NH2--+ C_H_/NT+ CH -

HCaN-+ C_H,/N..++ CH -

CH,--, C_HT- H2+

H2-_ CH[- -

H_-_CHT+C__H_--+C_H++ H2--

C2H4-_ C?H T- CH4+

C__H4-_ C_H_+ H_- H2

C_H4--+ C_H_'-- H_-

C2H6_ C._HT- CH4+

C_.H6--.C_H_-= H2+ H2

N -_ H2CN*= H +

N -_ HCN++ H2_-

NH_-_ NH[+ CH2_-

NH3-_ C_HyN.*+ H2_-

HCN --+C_H_N++ -

CHaCN-+ H2CN*_- C_H4-

CH_CN-+ C_H[- HCN "

CHaCN-_ C_HyN[+ -

CHaNH_-- C_H,,NT- CH4-

CH_NH_-- C_H,,NT- CH_-

HC:{N-_ C_H[- HCN -

HC:{N-_ C_H,,N-" -

NH -_ H_CN _- H_-

H?-- CHT- -

H_-_ CHT- H-

CH.)--+ CHT- CH._-

C2H_--_ C:H_- CH._-

C:Hu--C_,HT-CH_-C:H_-_ C_H,7- H_- H

C:H.)--_ C,H T- CHi-

C_H4--" C_,HT- CH:_--+

C_,H.I-+ C_H v - H?- H

C_H6-_ C.,HT- CH-l= H_

NH:v-+ NHT- CH.i-

NH:_---* NH?- CH:_-

NH3--_ CHT- NH2-

HCN --, HoCN-= -

HCN --. C.HyN[+ H --

CH._NH2---. C.H_N_-+ CH4-

CH3NH2---* C.H_NT+ CH4-- H

HC3N_ C.HvN_+ CH:{-CO -_ HCO*- CH:_

NH ---+NH.:. CH4_-CO --.HCO*- CH4+

C_H_-_ C2H_+ CH.,-

C2H4-+ C.:H++ CH.,+

C_.H6-_ C2H[- CH4+

CH3NH_-_ C_H_N: +* +

7.350

1.160

4.1001.000

1.200

1.1001.100

1.200

3.500

4.600

5.240

1.480

1.570

1.040

2.350

2.350

1.800

1.620

2.000

1.040

6.660

9.000

9.900

1.210

1.670

i.O00

7.400

1.100

3.000

1.500

1.130

1.230

1.510

1.700

2.600

6.000

1.910

1.610

1.490

6.320

3.230

6.600

1.320

8.800

2.500

1.400

7.100

9.900

1.560

1.500

1.200

2.250

× 10- io

x i0- 1!)

× 10 -9

× lO-:m(T./3OO)°'°°exp(-O.OOtT_)[M)× 10 -_

x 10- 13

× lO-_S(T_/3OO)°'°°exp(--O.oo:r_)iM __× I0-_

x I0- io

x 10-ll

x 10- lO

x 10-9

× 10- m

× 10 -m

x 10 -it

x 10 -it

x i0- lo

× 10 -9

× 10- io

x 10 -9

× 10- m

× 10 -ll

× 10- l,

x 10 -_

.,, 10 -_

.< lO--":(T,,/3OO)".U%xPt-O.OO_T_)13Ii× 10 -Ic)

× i0-:S(T,,/300)"'"%xp(-0.00/T,,)iXI7,< 10 -il

x 10 -_j

lO -!t

x 10 -!i

"< 10- i,

x i0 -_

:<10- 1,)

× 10 -_

× 10-_

× i0 -_

× i0 -_

× 10-ll

× 10 -9

x 10-ll

x I0-9

x 10- io

,<I0-9

× I0-_}

× I0- "_

× 10 -I°

× 10 -_!

x i0 -_)

X 10 -9

x 10 -9

CH_+ HC:{N-_ C_HyN-- CH.,-

CH++ NH3--* NH[+ CH_

CH_++H--CH:+re.-C++ H2-_ C2H +: H -

C_+ CH4--* C2H*a- CHi-

C++ CH4-_ C,_,H_:+CH__-

C++ CH4_ C_H_-+ H2: H

C++ CH4---, C,H++ H2,

c_ + cm--. c_H;+ H-C++ C,_H2---_ CzH++ H --

C_+ C2H4---* CzH_-+ H2-

C++ HCN ---* C2H++ CN -

c_++ _cN -. c_H; + N-C++ HCN ---* C_HyN. +-- H -

c[ + .C_N--.c,u_+ -C++ HC3N---* CzH++ HCN --

c; + Hc3N-. c_;+ CN-C++ HCsN---, C, HvN +-- C2-'-

C++ HC3N---, CzH_N[-- H --

C_+ C2N_-_ C_N += -

C++ C.zN2-_ C_HyN +- CN -

C_+ C,_,N2-* C_H_-- N__-

C:+ NH -. C,H,jN.*- H -

C'2H+_- CH4-+ C2H_- CH.{-

C._,H+ +

C2H++

C2H++C..,H+ +

C_,H++

C.,H+ +

C,H++

C..,H+ +C2H++

C_H++

C_,H++

C_H++

C.2H++

C,2H_+

C,_,H[+C2H++

C2H++

C2H++

C2H++

C2H++

C_H++

C2H++

C2H++

C2H+4-

C2H2++

C.,H++

CH4_ CrH_" H'2-

CH4-_ C;H,_- H -

CH.,-_ C_H_- -

C._,H2--C_H,_- H -

H2_ C:H..T, H -

N --*C.2N_: H -

HCN _ H2CN-- C:-

HCN -_ C,HvN-- H -

HCaN--' C,H_- HCN -

HC:,N---' C_H,_- CN -HC:_N--. C_H_S-= C,-

HC3N-_ C_HvN-- H -

CH4-* C_H +. H_,-

CH4--_ C_H,_, H -

C.,H_---, C_H_-- H_-+ H-C2H2-. CrHy --

C2H4-_ C2H[- C2H_-

C2H4-" C_H +- CHa-

C2H4-. C_Hy+- H .

C2H6-_ C,2H[- C2H_=-

C2H6--* C_.H+- C_H_-

C2H_--* C_H +" CH:_- H2

+ CH4-C2H6-_ CtHy -

C2H6--_ CxH_-+ CH:{-

C_H6--_ C_H_'- H2-+

C2H6 --_ CxH_ - H -

4.500

2.300

1.500

1.400

2.380

1.8201.960

5.740

2.100

1.200

1.900

2.600

7.800

1.560

2.310

5.610

1.290

1.980

1.020

7.500

4.500

3.000

3.300

3.740

3.740

1.320

1.000

1.200

1.700

1.000

1.350

1.3508.800

6.160

1.100

1.800

3.680

1.230

5.160

5.880

3.750

7.950

3.300

2.630

1.310

8.760

1.460

7.880

7.300

1.310

x 10 -9

x 10 -9

x i0- Io

× 10 -_

x 10 -1°

x 10- io

x 10- to

x 10- 1o

x 10- I,:,

x 10 -9

× 10-9

x I0 -l°

× 10- m

X 10 -9

x 10- _o

x i0- to

x 10-_

x 10- lo

X 10 -9

x 10- _o

x 10- 1o

x 10- 1,_

× 10- *''_

x 10- 1,,

× 10-1''

:< 10 -1_

x 10-e"(Tn/300)"-°"exp(-0.00/Tn)i.XI!x 10 -_

× 10-"

× I0 -i_*

x 10-_;

x 10 -9

x 10- i,_

x 10 -I''

x 10 -:_

x 10-"

x 10- l,_

x 10 -!_

x 10- ao

x 10- a.

x 10- 1o

x 10- _o

x 10- to

x 10- to

x 10- 1o

X 10 -ll

x I0-t_

x 10- n)

x 10 -_t

x I0- _o

C2H_+

C2H_+

C2H_+

C2H_+

C2H_+

C2H++

C2H_+

C2H_+

C,2H_+

C_H_+

C2H++

C_.H++

C2H_++

C2H++

C_H++

C,:H++

C2H++

C2H_+

C2H++

C_N++

C2H++

C2H_+4- ,

C.2H:i-

C.,,H_ +

C,,H:]-+-_ 4- ,

C._,H, i -

C.2H++

C.:H_ +

C_H_+

C_H_?-

C2HI_

C_HI+

C..,H_ +

C..,H_-+-t- ,

C_ H_ -_

C.2H_+

C2HT+

C._,H _++

C_H++

C2H++

QH++

C_H.,++

C2H_+

C.2H++

C'2H_+

C2H++

C2H++

C,.,H++

C_H++

C_H++

N -_ CH++ HCN "

N -_ C2N +-_ H2+

N -_ C_HyN_= H -

NH_-_ NHf+ C2H2+

NH3--* NH_- C2H+

HCN -_ H2CN++ C2H-

HCN -_ C_HvN +_- H -

HCN -_ C_H,jN += -

HC3N-_ C_H_7+ HCN -

HC3N-_ C_H,/N++ -

H_ C2H_+ H +

CH3NH2--_ C_HyN=++ C_H-

CH3NH2--. C_HyN++ C_H_-

CH3NH2--_ C_HyN +-- C_H_--

CH3CN--* C_HyN:++ C,2H-

CH3CN--_ C_H_+ CN -

CH3CN_ C_Hy++ HCN -

CH3CN--_ C_HyN++ +

H2-_ C_H++ -

HCN -_ C_H_N++ -

NH --*C_H,jN[+ H -

CH4-_ C_H +" H'2-

C2H2-_ C_H,_+ H2-

C2H2-_ C_H_- C_H2-

C2H4-_ C_H-- C_H_-

CuH_-- C_H?- C_,H4-

C:H_-_ C_H,_- CH.,-

C2H6-_ C_H_, H_-

HC:_N-- C_H,,N_- C.,H:-

C:N2-_ C_H,,N=-- C_H:-

C_N2-_ C_HvN:-- -

HCN _ H_CN _= C_H_-

C_N_-_ C_H_N[- C:H_-

H -_ C_H_+ H_,

N -_ C_H_NT" H_-

C_H_-_ C_H_- CH:{-

C_H2-_ C_H_+ H -

C2H4--* C_H_+ CH:{-

C2H4-_ C_H_+ H -

¢ CHa-C_H6--, C_H_ -

C_H_---, C_H;--'- CH,_-.-

NHa---, NH_+ C2H4-'-

NH3--, NH_-.- CeH3±

HCN ---, C_H_,N..+-:- --

HC_N---, C_H_N.++ C2H_-

H ---* C2H+, - H2+

CH4--, CzH_--- H_-r

Cell2--, C,H_+ CH4-

C._H2---* C,H_++ H_,-

C_H_---, C_H;-+ CH4+

C'_H6---_ CrH++ H2_

2.500 ×

7.500 ×

1.500 ×

1.240 ×

1.860 ×

6.720 ×

3.780 ×

5.000 x

1.480 x

2.220 ×

1.000 ×

1.300 x

7.560 x

6.480 ×

8.360 ×

1.060 ×

1.060 ×

5.000 ×

1.200 ×

4.200 ×

6.500 x

2.000 x

2.160 ×

5.040 x

9.300 ×

2.910 x

2.480 x

8.060 x

3.800 x

5.500 x

1.000 ×

1.600

4.000 x

1.000 x

2.200 ×

6.730 ×

2.370 ×

7.190 ×

7.110 x

3.710 ×

4.930 x

1.240 x

1.940 x

1.000 ×

1.100 x

3.000 ×

1.000 ×

6.840 x

1.220 x

3.550 x

3.270 ×

I0 -II

10-_1

10-_o

10 -9

10-_

10-_

10-_1

10-2S(Tn/300)°'°°exp(-O.OO/Tn) [M_10-_

10-9

10-1t

10 -9

lO-m

10-to

10-to

10-_

10 -9

lO-2S(T,/3OO)°'°°exp(-O.OO/T, [M]

lO-'_7(T,/3OO)°'°°exp(-O.OO/T, [M]10-_o

10-_o

10- 1o

10- _'_

10-_,,

10-_,,

10-1"

10- _':'

10-_

10-_'

10-1"

iO-:S(T,_, 3OO]'U"_expl,-o.OO"T, IM]10-_

10-1' _10- l,_

10-_"

10-_ _

10- 1o

10- m

10-_

10- ta

10-t2

i0-_o

10-9

10-_S(T,/300)"'°°exp(-0.00/T, [M]10 -9

10- ,o

10- t.,

10-tt

10- m

10-xo

10-_t

C.:H_+C2H6_C.H_+ CHq-C2H++NH3--+NH_+C2H4-C2H++CH3NH2--+CzH_N +- H2-

C2H++ HC3N---+ C_H_N +-' C2H4-

C2H++ HCN ---' H_CN +-' C2H4-

C2H_+ CH3CN---* C_HyNT-'- C2H4-

C2H_-+ C2N2---* C_HyN[+ C2H4-

C2H++ C2N_-* C_HvN.++ -

C.2H++ C,_H2---, C2H+_ - C2H_-

C2H++ C2H_---, C_H++ CH_-

C.2H++ C2H_---, C_H_+ H -

C2H++ C2H4---, C2H++ C2H6-+

C2H++ C2H6--* C.H v + CH4-

C_H6++ C2H6-_ C_H++ CH_-

C_H++ NH3---*NH_+ C2H6-

C2H++ NH3---* NH_+ C.oH5-

C._H++ H --*C2H_+ H2+

C2H++ CH4--* C_H++ --

C2H++ CeH_---* C_H_-+ C2H6-

C2H++ C=H4--* C=H[+ Co.H6-

C2H++ NHa-* NH++ C2H_-

C,2H++ HCN -_ H_CN += C2H_-

C._,H++ HCN --, C_H,_N_- CH4-N++ H2--*NH +_- H +

N*+ CH4-_ CH_= NH -

Y++ CH4--, CH_-- N -N +_- CH4--* H_CN-- H_--

N-+ CH4--* HCN _. H2- H

N++ C_H4-* C_H?+ NH2-

N*+ C2H4-* C_H_- NH -

N++ C=,H4-* C_H_+ N -

N_+ C.,H4---, HCN_+ CH:_-

N++ C_H4-* H2CN*= CH2-

N++ C_H4---* C_H,,N_: H_-

N*+ NH3-_ NH:[- N -

N*+ NH:{--*NH_- NH "

N*+ NH,_--*N2H +- H2-

N*+ CH:_NH_--* C_H_N: +: N -

N*+ CH3NH_--* C_H,IN:_- NH -

N*+ CH:_NH2-_ C_HyN[- NH_-

N++ CHaNH2--* H_.CN++ NH:_-4-

N++ CH3NH2-_ CH._ + N2- H2

N++ C_N_--* C_HyN++ N --

N++ C._N_--_C2N++ N2+

N++ HC3N--* C.H++ N2+

N++ HC3N--* C.H,N++ N -

N++ CO --*CO++ N -_

N*+ CO -* NO +-- C +

N++ NH ---* NH++ N --

N++ NH --, N++ H +

N++ HCN ---, HCN++ N +

NH++ HCN ---, H_CN++ N -

5.320

2.180

1.870

3.300

2.700

3.800

8.400

1.000

2.220

8.190

1.290

1.150

7.980

1.100

6.240

1.610

1.000

2.000

2.000

2.000

2.000

1.980

2.200

4.160

4.260

4.920

2.710

7.380

1.600

4.800

4.000

2.400

1.600

1.600

1.070

1.170

1.170

1.400

1.400

1.400

2.000

1.200

4.200

9.800

2.100

2.100

8.250

1.460

3.700

3.700

1.200

1.800

x 10 -_2

x 10 -9

x 10 -9

x 10 -9

x 10 -9

x 10 -9x 10 -_

x lO-:S(T./3OO)°'°°exp(-O.OO/T,)[M]x i0- m

x 10- to

x 10- 10

X 10 -9

x 10- _0"

x 10 -t_

x I0- to

x 10-9

X I0 -10

x 10-S(T./300)°'°°°exp(-84.00/T,)× 10 -9

x 10 -9

x 10-9

X 10-9

x 10- _o

x 10-_°exp(-41.90/Tn)x i0- 1,_

x 10-_

x 10- 1,,

x I0-_I

x 10- ;"

x 10 -1''

x 10 -1''

x 10 -i'_

x i0- i,_

x 10- I,,

x 10 -_

x 10 -_'_

x 10 -I"

x 10- _'_X 10 -9

x 10- I,

x 10- I,,

x 10- w

x 10- w

x 10 -10

x 10 -9

x 10 -9

x i0- _o

x 10- _o

x I0- _o

x 10- _o

X 10 -9

X i0 -9

NH++

NH++

NH++

NH++

NH++

NH++

NH++

NH++

NH++

NH++

NH++

NH++

NH++

NH++

NH++

NH++

NH++

NH++

NH++

NH++

NH++

NH++

NH++

NH++

NH++

NH$-_

NH++

NH2-

NH + _-

NH_-

NH_+T t

NH,, +NH,2+=NH:+

NH_+NH_+

NH_+

NH++

NH_+

NH;+NH_+

NH++

NH_+

NH++

N-.N2-. H +

NH _ NH_-;- N +CO ---. NO*--' H +

CO _ HCO*J- N +

Ho_---. NH,7- H +

H2--* H_- N -CH4-* CH_+ N +

CH4-* NH_+ CH3-

CH4-* H_oCN++ H.+ H

C_oH4--*C2H_+ NH3_-

C2H4--_ C2H++ NH2+

C2H4---* C2H_+ NH +

C2H4-* H2CN++ CH_t

C2H4--* C_HyN++ CH2-

C2H4--* C_HyN++ H2-

NH,_--*NH_+ NH -_

NH3-* NH_-+ N -

N_--*N_.H++ N +

CH._NHo.---* H_.CN++ NH3- H

CH3NH2--* C_H_N:++ NH_-

CH3NH_-_ C_H_N.++ NH.o-

CH3NH2--* C_H_N++ NH -

CH3NH2-" C_H_N++ N "

H2---, NH_-- H -

CH_-* NH_- CHa-

C2H4--' C'2H_-- NH,_,-

C2H4 -_ C2H_-- NH -

C2H4-_ C_H,,N_+ CH2-

C._,H4--_C_H,,NT= H -

NH:_--. NH_- NH_-

NH:_-_ NH 7- NH -

CH:{NH2-- C_H,,N.-: NH{-

CH:{NH_-- C_H,jN.7+ NH2-

CH_NH2-_ C_H,IN _- NH -

CH_NH2-" NHT+ H3CN -

NH -_ NH._: N -

H2--_NH_- H -

CH4_ NH]--.- CHa+

C2H4-_ NH_'- C2H3-N * NH,,-,-NH:{--, . H t -

CH:{NH2---, C. HuN[" NH:{-

CH,_NH2---, C_HuNT: NH-2-.-

CH:{NH._----, NH]-+ CH2NH2 -NH "*-'---_ NHt _- N +

CHaNH.'2---' C. HvN:++ NH_-

NH++ CH3CN_ C_HyN++ NH3,HCN++ NH ---, NH++ CN +

HCN++ CO ---, C_HyN++ CO =HCN++ CO ---* HCO++ CN _-

HCN++ CH4--* H2CN*+ CH_--,

HCN++ H2---* H=CN++ H +

HCN++ C=H2---, C2H_+ HCN -

HCN++ C2H2---, C2H_+ CN -

1.300

1.000

5.390

4.410

1.280

2.2509.600

1,920

6.720

1.500

3.750

3.750

3.000

1.500

1.500

1.800

6.000

6.500

4.200

1.050

9.500

4.200

4.200

2.700

9.200

4.500

3.000

t,500

3.000

6.900

1.610

4.000

1.100

4.000

1.000

7,300

3,100

4.800

1.400

4.700

9.000

6.300

2.7007.100

2.000

1.600

6.500

3.220

1.380

1.100

8.600

9.000

3.000

x 10 -9

× 10 -9

x 10- lo

x 10- it)

x 10 -9

x 10- _o

X 10 -I1

x 10- _o

x 10- to

x i0- _o

x 10-t°x I0- lo

X I0 -I0

x 10-_°

x i0-m

X 10 -9

x i0-_°

x 10- _o

x 10- _o

x 10- lo

x 10- _o

x 10- _o

x 10- lo

x 10- m

x 10- lo

x 10- _'9

× 10- 1,,

x 10- 1,1

x i0- I,_

x 10-1''

x 10 -_

x 10- ]_}

x t0 -_}

x I0- I_,

x 10- l,_

x 10- _o

x 10- t2exp(-241.00/T.]x 10- 1o

× 10 -!_

x 10-_*

x 10- w

x I0- _')

x I0- _o

x I0- _o

X 10 -9

x 10 -9

x 10- 1o

x 10- lo

x 10- _o

x 10 -_}

x 10- _o

x 10-m

x 10 -_')

HCN*+ C,2H2-_C_HvNT+H2-HCN++NH3_NH3- HCN+HCN++NH3--*H2CN÷-' NH_+HCN++NH_-_NHT=CN+HCN++HCN-- H2CN*+CN-HCN++HC3N-.C_H,jNT+CN-HCN++HC3N-_C.H_N_+= HCN-H_CN++NH3--_NH_, HCN+H2CN++HC3N--_C.H,jN[+ HCN-H=CN++CH3NH2--C.HyNT+HCN-H=CN++CH3NH2-_C.H_N++-H2CN++CH3CN-_C_HyN++HCN-H2CN++C4H2-_C4H_+HCN-N2++CO --_CO +. No_+

N_+ CH4----* CH_-- No_- H

N++ CH4---, CH_-.- N2-,- H__

N++ C2H_---, C2H_- N_.+

N++ H2--_ N2H *_ H -

N++ N --*N++ N2-

N++ NH3-_ NH_- N_÷

N++ HCN --*HCN*- N_+

N++ CH3NH2-_ C_HvN++ N_+N++ CH3 NH2----, +_-_ C_HvN. N2+ H

N_+ CH_NH2-- CH,_- NH2- N:

N++ HC:_N-_ C_H_N_:+ N__÷

N++ C.2N2--* C,Hr_N-- N_,-

N.7+ CH:{CN--* C,HvN_7+ N2-N$+ CHaCN-- C,H.,NT+ N,2+ H

N[+ CH:_CN-_ C_H._Nt+ N2_- H:

N_+ NH -_ NH-- N2-

N[+ H -_ H +: N2-N$+ C -_ C +- N_-

N2H*+ CH4--. CH_- N_-

N,,H+: C2H2--_ C_,H_- N_-

N._,H+_- C._,H_:_C,H:- N_,-

No_H++ HCN -- H_CN*_ N_,

N_H++ CH3CN-_ C_H,,N-+" N_-

N2H +-_ HC3N--* C_H,N=*+ No_.

N2H++ C2N2-- C_H,_NT+ No_-_

N2H+-_ CO -_ HCO-- N2+

CN++ H2-* HCN-- H +

CN++ H2-" C_HvN='- H -

CN++

CN++

CN++

CN++

CN++

CN++

CN++

CN++

CN++

CN++

CN++

CH4-_ CH$- HCN -

CH4--* CH[- CN -

CH4---+HCN*" CH3_-

CH4----+ H_CN-" CHo±

CH4--, C_HyNT+ H2+

C2H2_ C2H?- CN -+-

C2H2---* C_HyN[+ H +

C2H4 --_ C2H?- CN +

C2H4--. HCN +- C._H_+

C2H4--_ C_H,NT+ H2+

C2H6--. C.,H_- HCN + H2

3.000 × 10-t°

1.680 × 10-9

8.400 × 10-1°

1.400 × 10-*°

1.600 × 10-9

2.210 × 10 -9

2.390 × I0-_

2.400 × i0-_

3.400 × 10 -9

1.870 × 10 -9

2.310 × 10- to

3.800 x 10 -9

1.400 × 10 -9

7.400 × 10-tl

1.520 × 10-9

3,800 × 10-1°

4.300 x 10-I°

2.100 × 10-9

5.000 × i0-12

2.000 × 10-9

3.900 × 10-iO

7.200 x 10-11

8.760 × 10_1°

2.520 × 10-m

2.900 × 10-_

8.600 _ 10-1°

3.150 :', 10 -w

1.370 "< 10-_

4.200 "< 10- l,,

6.500 × i0-I"

1.200 × i0- _''

I.i00 "< I0 -_)

8.900 × 10- _"

1,410 < 10 -_

1.300 ,: 10 -_)

3.200 × 10 -9

4.100 × I0 -_t

4.300 × 10 -!)

1.200 × i0 -_)

8.800 x I0- _'_

5.500 x lO-I°

5.500 × lO-tt)

4.500 x 10-t°

1.350 x lO-l°

1.350 x lO-I_)

9.000 x lO-lt

9.000 x 10-11

1.350× 10-9

1.500 × 10-l°

7.000 × 10-_°

2.500 x 10-1°

5.000 x 10 -it

2.850 x 10-1°

CN+q- C2H6"-'*C.,H]--HCN- HCN++ C2H6---* C2H 7- HCN -

CN++ NH3--* NH$- HCN -

CN++ NH3--, NH_- CN --CN++ NH3---* HCN*- NH2--

CN++ NH3--. H2CN-- NH -

CN++ HCN -_ HCN-- CN -

CN++ HCN _ C_H.jN:-+ H -

CN++ HC:_N---, C_H,,N.++ CN -

CN++ HC3N-* C:HyN[+ HCN -

CN++ Co.N2--*C_H_NT+ CN -

CN++ C2N=--* C_H_NT+ No_--

CN++ C2N_--* C2N-- CNN -

CN++ CO -_ CO'- CN -

CN++ NH -_ NH-: CN -

C2N++ CH4----_ C2Hf- HCN

C2N++ CH4--* H2CN-- C._H.o-

C2N++ CH4--* C_H_NT+ H2+

C2N++ C2H2--* C_H_-+ HCN -_C2N++ C2H2-_ H2CN-: -

C2N++ C2H4-_ C)H[- -

C_N++ C2H4-_ C,H.,NT+ C)H_-

C_N++ C2H4--* C,H._- HCN - H

C2N++ C2H4---. C_H._- HCN -C.,N÷:

C..,N++C2H.I-_ C,H._S[- C:H.,-

NH3-_ H.,CN-- HCN -

C'_,N+: NHa-_ N_H-- C_H_-

C._N+: CH:_CN-- C,H$: C2N_-

C2N += HC:,N-- C:H_, C2N2-C.,N "_- H2--_ H2CN-- C -

HCO++ C=,H.)---C:H7- CO -

HCO*+ C_H6-- C:H-- CO -

HCO*+ NHa-- NH_- CO -

HCO *- HCN -- H_CN-: CO -

O++ N2--_ NO-- N -

O +J- CHaNH._-- C_H:,ST- O -

O++ CH:{NH2-- C.HvNT: -

O++ CH3NH_-_ C,H!_N.7- -

O++ CH4-_ CH[- O -

O++ CH.,-, CH_'- -

O++ C2H6---. C2H_-- -

O++ C2H6--* C2H?- --

O++ H2--* OHP - H -

CO++ H--* H +- CO-

CO++ H2-_ HCO'- H +

CO++

CO++

CO + +

CO++

CO++

CO++

CO++

CO++

CH4-* CH 7- CO -

CH4--, HCO-- CH_--

CH4--_ C,H_- H --

C2H2-* C_H.$- CO -

NH3--, NH_- CO -0 -_ O +: CO -

HCN -_ HCN--- CO -

HC3N--. C_H_N.*+ CO -

1.240 x 10 -_

3.800 x 10-1°

1.000 x 10-1°

1.200 × I0 -9

4.000 x i0-i°

3.000 x I0- lO

1.780 x 10 -9

3.150 × 10-l°

3.120 x 10 -9

7.800 x 10-i')

1.190 x 10 -91.400 x 10-1°

7.000 x 10 -1!

6.300× 10-1°

6.500 x i0-1°

4.200 x 10-t°

7.000 x 10 -11

2.100 x 10- m

1.470 x 10 -9

1.280 x 10-1°

1.200 x 10-v'

3.000 x lO-l')

3.600 x 10-1°

1.200 _ 10-1_}

3.000 x 10-t"

1.900 x 10 -_

1.900 x 10-1*'4.100 _ l0 -9

3.500 '_ 10 -'_

8.100"( 1O-t"

1.300 "<10 -!_

1.200 \ lO-i"

1.900 "< 10 -:)

3.700 , 10 -!_

t.200 ', 10- l"(T, _300] -'4 "_expt-0.00/T,)1.260 ,< 10-I'_

1.660 _ 10 -_

3.150 x 10- H,

8.900 x lO-h)

1.100 x 10 -w

1.330 "< 10 -9

5.700 x lO-t°

1.200 x l0 -9

7.500 x 10-_°

1.300 x 10 .9

9.790 x 10-m

2.990 x 10-m

8.I60 x I0 -_

4.100 x 10 -w

1.500 x 10 -9

1.400 x 10 -_°

3.400 x 10 -9

2.300 × 10-9

H++E-_H++H++ E--,H +H -H++ E _ H2+H-H_+E-,H÷H-HC+÷ E--,C + +CH++ E-_ C + H-

cH_+ s -_ cH + ff-

CH++ E -_ CH2+ H -

CHT+ E --,CH3+ H -

CH++ E --,CH2t H . H

CH_+ E -_ CH4÷ H -

CH_+ E -_ CH3+ H2-

CH++ E --,CH3÷ H - H

CHs++ E --,CH2+ H2- H

C++E-_C+C÷

C2H++ E --+CH + C -

C_H++ E _ C2H+ H -

C_H_+ E --,CH :-CH -

C2H_+ E -_ C_H2÷ H -

C_H++ E -, CH_÷ CH -

C2H++ E --,C_H3-r H -

C2H++ E _ CH2- CH.2-

C_H_+ E -_ C2H4- H -

C._H_÷ E --_CH3- CHo_--

C2H_-_ E -_ CH4. CH.2-

C_H+: E -_ CH4- H.2-N_+E-_N+-

HCN++ E-_ CN - H -

H.,CN*= E -_ HCN - H -

H2CN _= E -_ HNC - H -

H_CN +- E-_ CN- H- H

H_CN +- E -_ CH_- N -

H_CN +- E -_ H2- CN -

CN +-_ E-_ C- N -

C2N++ E--C + CN -

C_N+÷ E -_ C_- N -

HCO÷+ E-_ H + CO-

C_H:++ E --, C4H2- H -

NHI++ E ---* NHa- H -

0.0 0.0 0.0

NH_+ E ---, NH2+ H -

NH:_+ E --, NH 4- H2,

NH_++ E--* NH + H-NH++ E--* N + H-

N++ E --, N(2D)+ N -

N++ E --4N(2D)+ N(2D)+N=H++ E _ N2+ H -CO++ E-_C+ O

C2H++ E -_ C2H6-. H -

C2H7++ E --_C_H_- H._-

C2H7++ E --*C2H4_- H2- H

H + H -* H2+ +

4.000 × 10-12(Te/300)-'5°°

2.300 × lO-r(T_/300) -'''°°

4.400 × lO-S(T_/300) -'_')°

5.600 × 10-S(T_/300) -'n°°

4.000 × i0-12(T_/300)°'°°°

1.500 × 10-:(T_/300) -'4'_°

2.500 × IO-r(T_/300) -':'°°

3.500 × 10-r(Te/300) -5°°

1.750 x 10-7(T_/300) -'7'°°

1.750 × 10-7(T_/300) -'5°°

3.300 × 10-7(T_/300) -'27°1.100 × 10-7(T_/300) -'27°

3.300 x I0-7(T,/300) -'27°

3.300 × 10-7(T_/300) -27°

3.000 × 10-7(Te/300) -'5°°

6.500 × 10-S(T_/300) -'5°°

1.900 × 10-7(T_/300) -'5°°

8.I00 x lO-S(T_/300) -'5°°

2.300 × 10-7(T_/300) -'5°°

2.300 × 10-r(T_/300) -'5°°

1.750 × 10-7(Te/300) -.`.5o0

1.750 x 10-7(T_/300) -_°°3.700 × 10-7(T_/300) -'_°°

3.700 × 10-;(T_/300) -'_C)°

3.700 _ 10-;(T_/300) -''_°°

3.000 -,' 10-:(T,,/300) -'SqJ°

1.000 , 10- I-'(Z/300) ".ooo

5.000 ,: 10-:'(T,/300] -':'°°

5.530 x i0-'_(_,/300} -':''_"

5.530, lO-S(T_ /300) -':''l_

5.530, 10-_(T,,/300) -''3'"_

9.240, lO-_(r,/300) -:'_

9.240 x 10-S(T_/300) -'5°°

5.000 × lO-:(T_/300) -:'°°

3.000 x lO-:(T_/300) -':'`)°

1.500 × 10-r(T_/'300) -'_)°°

1.500 x 10-7(T_/300) -'5°°

2.400 × 10- 7(T_ /300) -'(i9°6.200 x 10-;(T_/300) -'_°°

3.800 x 10-7(T_/300) -':)°()

1.650 x 10-7(T_/300) -'5°°

1.650 x 10- 7(T_ /300) -'5°°

3.000 x lO-:(T./300) -_°°

4.300 x 10-S(T_/300) -'5_°

1.940 x 10-7(T,/300) -39°2.600 x 10-S(Te/300) -'39°

1.700 x 10-:(T_/300) -'5°°

1.600 × 10-7(T_/300) -5°°

1.000 × 10-7(Te/300) -'5°°

1.000 x 10-7(T¢/300) -'5°°

1.000 × 10- 7(T¢/300) -_°°9.O30 x lO-33(z./aoo)-'.a%xp(-O.OO/T.)[M]

10

N(eD)_- N__---,N - N_-N('_D)_-CH4--,NH+ CH:_-N('_D)+C._H2---,CHCN- H -N(2D)+C_H4--*NH -- C_H3--N(2D)+NH3--,NH - NH_,N(2D)+H2--*NH+ H -N(eD)+CO--*N + CO-N(2D)÷O--*N+ O+N(2D)+NH --*N_.--H -N + CH2--*HCN+ H-N + CHn-_ H2CN+ H =

N + CH3-_ HCN + H- H

N + H_-_ NH + H

N + H_CN-_ NH - HCN -

N + CH-_CN ,-H-

N + C2-_ CN + C--

NH + H--* N + H_.+

NH + N-_ N2+ H

NH + Nil --_N2+ H2+

CN - CH4-_ HCN + CHa-

CN + C2H_--_ HCN --C_.H_-

CN + C._H2-_ HCaN÷ H -

CN -- C2H4--* - H -

CN + HCN -_ C._)N_-H -

CN _-CH:{-_ CH_CN- -

CN + CH._)-_CH - HCN -

CN -_CH.{--_HCN - CHi-

N :-CN-_ N_- C-

NH- CN -_ HCN- N-

H..)+CN -_ HCN - H -

HCN - H -_ H_CN- -

HCN - C=,H-_ HC:{N: H -

H__CN- H -_ HCN - H_-

CHCN - N -_ C_N2- H -

CHCN - CHCN -_ C._N_- H_-

CaN+ CH._ HC:_N-- CH:{-

C3N+ C.,H_-_ HC:_N- C:H_-

HCaN" H --* H2C3N- -

HC:,N: CN _ C.,N,_,-H -

H2C:,N- H -_ C2H._--HCN -

C2N2+ H -_ HC2N.,-_ -

HC2N.,- H -_ HCN + HCN -

CH + CH4--* C2H4-- H -

CH + O-_ H + CO-

CH + O--, OH + C _-

CH + Ho.--,CHa+ +

ICHor- N._-. CH2+ N.,-

ICH2-r H._--,CH2+ Ho_-r

ICH2_- H._--*CH3+ H +

ICH2+ CH4--* CH_.+ CH4-

9.400 × 10-14(Tn/300)u'°°°exp(-510.00/Tn)

1.500 × 10-l"_(Tn/300)°'5°°exp(-0.00/Tn)1.000 × lO-11(T,/300)°'5°°exp(-O.OO/T,)

6.000 x 10-_l(T,/3OO)°'5°°exp(-O.OO/T,)

5.000 x 10-tl (T,/300)°'5°°exp(-0.00/T,)

1.700 × 10-'2(T,/300)°'5°°exp(-0.00/Tn)1.700 × 10-'2

6.900 × 10-t3(Tn/300)°'5°°exp(-0.00/T,)1.O00 × 10-1°

5.000 x 10- _texp(-250.00/T,,)

4.300 x 10- Wexp(-420.00/Tn)8.600 x 10 -11

5.200 x 10-t°exp(-16000.00/Tn)3.900 x 10 -11

2.100 × 10-tl(T./300)°'5°°exp(-0.00/Tn)

5.000 × lO-H(T,/3OO)°'5°°exp(-O.OO/T,)

8.200 × lO-"(T./300)°'68°exp(-950.OO/T.)

1.900 × 10-t°(T_/300) °'5°°

1.000 × 10-33(T./300)°'°°exp(-O.OO/T.)[M]

7.300 x lO-t3(Tn/3OO)2"3°°exp(-16.00/Tn)

5.600 x 10-t2(T,/3OO)t'S°°exp(-5OO.OO/T,)

2.900 × 10-1°(T_/300)-53°exp(-0.00/T,)2.500 x lO-m(T./3OO)-"4°exp(-O.OO/T.)1.800 × lO-it

1.000 x 10-16

5.300 x 10-t"(T,,/300)°'°°°exp(-2500.00/T,]

9.210 × 10- _(T./300)')'7°°exp( - 1500.00/Tn)

1.000 × 10-_°(T,/300]°°°°exp(-50.00/T,)

2.940 _ 10-i:2(T,/300)u"_°°exp( - 1000.00/T,)

2.600 x 10- _ (T, _300]"'°°°exp(-2OTO.OO/T_)

k,-, = 7.110 × lO-:'"(300/T,,)"expt-12OO.OO/T,)iM ]

k.,c = 9.200 × 10-_2exp(-1200.00/Tn)iM]2.200 × 10 -_''

7.000 ,. lO-_t

1.000 ',<10- _e

5.000 x 10-_t

5.000 '< 10- 14

1.0O0 × I0- _

k,_= r.llO × 10-:_°(300/T.)%xpi-1200.OO/To)iM]k_ = 9.200 x 10-_2exp(-1200.00/Tn)[M]1.000 x I0-_

1.500 x 10- _

kc, = 7.110 x lO-3°(300/T,_)"expt-O.OO/Tn)[M]

k_ = 1.500 x 10-iSexp(-0.00/T.)[M]

1.700 x 10-taexp(-ll0.00/Tn)1.000 x 10-t°

4.750 × I0-tl(T,_/3OO)U'5°°exp(-O.OO/T,)

4.750 x I0-t'(T,/3OO)°'5°°exp(-O.OO/T,)

2.500 × 10-3°(T,/300)"'°°exp(-O.OO/T.) [M]7.900 × 10- _'-'

1.000 x 10- _

7.000 x 10-_2

1.600 x 10- t'2

11

ICH_.+CH4-*CH_+CHn=CH._+CH._--*C._H._+H2,-CH2+C2H2--*C3H4+ -

CH2+H --*CH- H2,CH3+CH3---_C2H6+-

CH_+ H --+CH4_- +

C4H_t H --_ C4H3-r

C4H3+ H --, C4H2+ He+

C2+ H2--' C2H* H +

C2+ CH4--_ C2H-r CH3+

C_H+ H2--*C2H2+ H +

C._H+ CH4--* Co H._+ CH_+

C_H+ C2H_-_ C4H2+ H +

C2H_+ H --*C2H:_,--

C2H4+ H---,C2H_:

C,2H,_+H --*C.oH2+ H2-

C2H5+ H -_ CH_-- CH:_-

C + H_--* CH*- Ho.-

C + H:_ CH*- H -

C + CH_-_ C_H-= H_-

C + CH?-_ CH-: CH4-C + H_CN'-- CHT- CN -

C + CN--_ C-- CS -

C + CH.7-- C.,H-- H -

C _-NH_-_ CH -= NH -

C + HCN*-_ CH "- CN -

C - C.,H--, C_II,_- H -C ± N_H'-_ CH-= N.,+

C ,-NH._-_ CH?- NH +

C + C,_,H:_-_C_H,_-- H -

C + CH?-_ CH-- CH,-

C + NH-- CN - H-

C + NH.,--._-H -

C + H_-. CH2- -

C + N2-.CNN--

C+CO--+-

C+N-_CN--

C+C-.C_+-

C + H-_ CH-- _-

C + O---,CO-

C + CH--,C2+ H +

C + CNN--,CN-- CN +

CNN + N --, CN + N__+

CNN + H --, CH -- N_+

CNN + H--* CN- NH +

CNN + C2H2---, _ +

CNN + C._H4--* - +

1.900 × 10 -I2

5.300 × 10-11

kn = 7.600 × lO-25(300/T,)"exp(-O.OO/T,)iM}

k_ = 5.900 x 10-t2exp(-0.00/Tn)[M]

4.700 × 10- _°(T,_/300)°'°°°exp(-370.00/T,)

kn = 1.300 × lO-'r3(3OO/T,)2exp(-O.OO/Tn)[M!

k,,c : 5.500 x 10-tXexp(-0.00/Tn)[M]

k,_ = 1.700 x lO-'2r(3OO/T,)2exp(-O.OO/Tn)[M!

k_ = 1.500 × 10-1°exp(-0.00/Tn)iM]

ko = 1.390 x lO-l°(300/T,)"-exp(-1.18/Tn)i.M]

k_ = 1.000 x 10-12exp(-1.18/T,)[M]1.200 x 10 -11

1.400 x 10- l'_

1.900 x 10 -tl

1.900 x 10-llexp(--1450.00/T,)

2.800 x 10-12exp(--250.00/Tn)

6.700 x lO-ll(T,/3OO)°'5°°exp(-O.OO/Tn)

ko = 7.110 x lO-3°(300/T,)2exp(-12OO.OO/Tn)iM!

k_ = 9.200 x X0-12exp(-1200.00/Tn)[M]

k,_ = 1.220 x lO-28(300/T,)2exp(-1040.OO/T_)iM]

k_ = 3.700 x 10-11exp(-1040.00/T,)[M]1.500× 10-11

1.900 x 10- mexp(-440.00/Tn)2.000 × 10 -_

2.400 × 10 -9

1.200 ",: 10 -_

1.200 × 10 -_

1.200 × 10 -_

1.100 x 10 -_*

1.200 × 10 -_

1.200 x 10 -_

1.100 × 10 -_*

1.100 × 10-'

1.100 × 10-_

1.000 x i0-_

1.100 x I0 -_

1.200 × 10-_

2.000 × 10- _

2.000 × lO-_l(Tn/3OO)°'5°°exp(-O.OO/Tn)

1.420 × lO-:'l(T,/3OO)-_°°exp(-O.OO/T,)[M!

6.200 × lO-33(T,/300)-2"°°exp(-O.OO/T,)[M!

1.260 × 10-:_t(T./3OO)-2"°°exp(-O.OO/T.)[M!

1.000 × 10-'r(T,/300)°'°°°exp(-0.00/T,)1.000 × 10-";(T,/300)°'°°°exp(-0.00/Tn)

1.000 × 10-'Z(T,/300)°'°°°exp(-0.00/T,)

2.100 × 10-m(T,/3OO)°'°°°exp(-O.OO/Tn)

1.730 x lO-'t(T,/3OO)°'5°°exp(-O.OO/Tn)

1.000 × 10-'°(Tn/300)°'°°°exp(-0.00/T,)

1.000 x 10-m(T,/3OO)°'°°°exp(-O.OO/Tn)

5.000 × lO-"(T./3OO)°'°°°exp(-O.OO/T.)

5.000 × 10- "(T./300)°'°°°exp(-0.00/T,)

1.000 × 10-l°(T,/3OO)°'°°°exp(-O.OO/T,)

1.000 × lO-'°(T,/3OO)°'°°°exp(-O.OO/T,)

12

H2÷NH2---_NH:_-H-C + NH2---_ + H -

O ÷ NH_.---_ -- H -

O ÷ NH2--* NH - OH -

6.320 x 10- :' (Tn/300) 0.176exp(-0.00/Tn)

2.000 × 10-" (Tn/300)°'5°°exp(-O.OO/Tn)

3.200 × 10-:2(T_/300)°'°°°exp(-O.OO/Tn)

3.500 × 10-:2(Tn/3OO)°'5°°exp(-O.OO/Tn)

13

_/_/e _: Selected Proton Affinities _

Neutral Ion Proton

Species Produced Affmit3-(eV)

H H + 2.69N NH* 3.37

H2 H + 4.39CO COH + 4.74

N2 N2H + 5.13

CH3 CH_ 5.62

CH4 CH[ 5.72C2N C2NH + 5.75

OH H_O _ 6.16

C2H6 CeH_ 6.23

C2H5 C2H_- 6.42

C3H8 C3H 9 6.,50

NH NH_ 6.62

C._,H2 Cell 3 6.69

C3H7 C3H[ 7.03

C2H4 C2H_ 7.05H20 H30- 7.24HCN HCNH" 7.46

C2H3 C,2H_" 7.56

HN3 H.,N_- 7.76

CH3CCH CH3CCH,T 7.78c-CsHs ( c-C3H6 ]I:I" 7.50

C4H2 C4H_- 7.79C3-_2 C3_N2H* 7.81

C,2H C2H__ 7.95

NH2 NH_- S.13HNC HCNH* S.14

CH3CN CH3CNtl _ S.18

CH2 CHCN CH2 CHCNH _- S.23

CH2 CH_ 8.56

NH3 NH_- 8.85

N_H4 " *_ _N__H5 8.87CH3NNCH3 CH3NHNCH3 + 8.97

CH3 CHNH CH3 CHNH + 9.15

CH2 CHNH: CH3 CHNH + 9.37

CH2 NCH3 CH2 NHCH_ 9.41

a Computed from data taken from Lias et al. [1988]

,ooo 1' "' "'"'...2500 TITAN

zoooH2 --_

._ _5oo

I000 c_N_4

4 6 8 1.13 1;3LOG DENSITIES (cm o)

3000

2500

i1500

I I I I

1000

-2

I I

rNx +

-1

I I

0

I i I I

1

I.OG DENSITIES (cm -a)

2

N2H +

3 4

j_

3000

DR

E

q)"O

°F,,4

<_

2500

2000 -\ H

1500 --

1000

-3 -2.5 -2

log

-1_5 -1

(l,oss rate

-.5-3 -!

(cm s ))

0 .5

3000

2500

N=H*

produ

2000

i1500

NH + + N=

1000

-4

3000

-3 -2 - I 0

DR

2500|OSS

_15oo C=H=

1000HCN

-4 -3 -2 o_.,1.o<;pRoDuc'no,oz _SS*_VZ(c= S')

3000

2500

_2000

1500

I000

30O0

2500

_2000

5oo

1000

+

c[-L

C_H3* + HCN

N + + CI'L

-4 -2

DR

HC3N

+ HCN

I

0

-4 -2 _)SLOG PRODUCTION OR LOSS RATE (CM- -')

0

!

s ma)((,_ __1-

olg_ uo!lonPOad)

8- g- m

000!

009l

0008

O00g

-8 - 1 -I)FLUX(cm s leV- steradian

0

I

).-

q

v

)--

v

Z _,.y.

m

m

v

m

m

im

T

m

-- m

_'_ t,

i , I

i

_, i i , r

7!

m

I

F

,m

---,o.,P

bl _'.

b.