The High-Resolution Infrared Spectrum of 34S16O2

up to 4000 cm-1

J.-M. Flaud, W.J. Lafferty, R.L. Sams,

and El Hadji Abib Ngom

IntroductionIntroductionThe spectrum of sulfur dioxide is obviously of interest as an

atmospheric pollutant monitoring tool especially after a volcanic

eruption. It is also present in the Venus atmosphere and has recently

been discovered in the atmosphere of Io.

The spectrum of the normal isotopic species, 32S16O2 has been very

well studied. However, that of the 34SO2 species which is 4%

abundant has only been studied in natural samples.

In this work we have recorded the spectra of a number of bands

of a sample enriched to 95.3% in 34SO2 and retrieved much

improved spectroscopy constants of this isotopic species.

The fundamental bands: ν1 (8.7μm) ,ν2 (19.5μm) , ν3 (7.4μm)

The combination bands: ν2 + ν3 (5.4μm) ,ν1 + ν3(4.0μm) 2ν3 (3.7μm) and 2ν1 + ν3 (2.8μm). The hot bands: 2ν2‑ ν2, 3ν2‑ 2ν2, ν1 + ν2‑ ν2, ν2+ ν3 ‑ ν2, ν1+ ν2+ ν3‑ ν2

Bands of 34S16O2

Accurate rotational levels for the:(000), (010), (020), (030), (100), (001), (110), (011), (101), (002), (111), (201) vibrational states.

EXPERIMENTAL DETAILS

Sulfur dioxide sample enriched in 34SO2 (95.3 %) Bruker IFS 120 HR (PNNL) evacuated to about 4 Pa (0.030 Torr). Potassium bromide beamsplitter. Detectors:Liquid helium silicon bolometer from 410 cm-1 to 660 cm-1 Mercury cadmium telluride from 1000 cm-1 to 2000 cm-1Indium antimonide detector from 2200 cm-1 - 3700 cm-1.Pressure measured with three MKS Baratron manometers (1, 10 or 1000 Torr full scale) (stated uncertainty of 0.05 % of full scale).Cells: 19.94 cm cell temperature regulated to 24.36C +/- 0.1 C White type long path cell at room temperature of about 21.5+/- 1.0C

LIST OF SPECTRA

Spectral region (cm-1)

Resolution(cm-1)

Number ofScans

PressureMillibar (Torr)

Optical path length (cm)

T(C) Calibration

1000-1419 0.0018 320 1.5935 (1.205) 19.94 24.36 N2O [7]

1000-1419 0.0018 320 0.6612 (0.500) 19.94 24.36 N2O [7]

1000-1419 0.0018 320 0.2862 (0.2164) 19.94 24.36 N2O [7]

1000-1419 0.0018 320 0.1298 (0.09815) 19.94 24.36 N2O [7]

1000-1419 0.0018 320 0.06228 (.0471) 19.94 24.36 N2O [7]

2200-2600 0.0035 32 0.2909 (0.220) 320 21.5 CO2 [8]

2200-2600 0.0035 32 0.7987 (0.604) 320 21.5 CO2 [8]

2550-2920 0.0035 64 1.3449 (1,017) 1280 21.5 HDO [9]

3500-3700 0.0040 256 1.340 (1.013) 1280 21.5 CO2 [8]

1600-2000 0.0025 320 2.076 (1.570) 1280 21.5 H2O [10]

410-660 0.0018 80 0.898 (0.679) 320 21.5 CO2 [8]

410-660 0.0018 80 0.2175 (0.1645) 320 21.5 CO2 [8]

Initial line assignments performed: either by following line series and using combination differences to verify the J and Ka assignments, or by using predictions based on the corresponding spectra analyzed for the main isotopic species.

ANALYSIS

Then the various ground state combination difference obtained in this work were used together with all existing microwave, sub millimeter and terahertz rotational frequencies to obtain an improved set of ground state rotational constants.

Finally these GS constants were used to calculate the upper state energy levels of the assigned bands..

HAMILTONIAN MODELS

(020) (100) (001)

(020) HW Herm conj Herm conj

(100) F HW Herm conj

(001) CC HW

A-type Watson Hamiltonian written in the Ir representation

Except for

C1h

F = hF Jxy2

CC = i*Jy J2 + ( J-

3 - J+3)

C2hC2h

Ch2

J± = Jx -/+ iJy

LINE POSITIONS:RESULTS(1)

Vibrational State (010) (100) (001) (020) (110) (011)

Number of levels 1186 807 1222 794 349 608

JMAX 74 62 77 60 42 57

Kmax 28 23 24 22 16 19

0.0000≤δ<0.0002 96.2% 82.7% 69.0% 66.3%

0.0002≤δ<0.0004 3.0% 12.2% 24.7% 24.9%

0.0004≤δ<0.0015 0.8% 5.1% 10.3% 8.8%

Std. Deviation (10-3 cm-1)

0.1 0.2 0.24 0.25

Vibrational state (030) (101) (002) (111) (201)

Number of levels 126 863 488 350 413

Jmax 44 66 57 45 47

Kmax 6 23 18 15 13

0.0000≤ δ <0.00020.0002≤ δ <0.00040.0004≤ δ <0.0019

72.2%20.6%7.2%

59.1%25.6%15,3%

36.5%28.3%35.2%

49.4%30.9%19.7%

33.7%22.0%44.3%

Std. Devi, (10-3 cm‑1) 0.25 0.32 0.48 0.34 0.58

LINE POSITIONS:RESULTS(2)

Obs. and calc. spectra of the ν1 band of 34S16O2 showing the distinctive b-type contour of the band.

LINE INTENSITIES

Nb of fitted intensities: 359

Statistical analysis: 0% <δI/I < 3% 66.6 % of the lines 3% < δI/I < 6% 23.4 % of the lines 6% < δI/I < 12% 10.0 % of the lines

Weighted Standard Deviation: 0.94D+00

32SO234SO2

32SO234SO2

S(ν1) 0.3513(8) 0.3452(17) S(8.7μm) 0.38286(90) 0.3767(15)

S(ν3) 2.721(4) 0.2673(13) S(7.3μm) 2.9657(43) 2.959(10)

Total band intensities (10-17 cm-1 /(molecule cm-2) at 296K

The Q-branch of the Ka = 9-10 subband of the b-type ν2 band of 34S16O2

Small portion of the R-branch of the a-type ν3 band of 34S16O2

Obs. and calc. transitions of the a-type 111-010 hot band. The transitions of the ν1 + ν3 band are off-scale. The lower-state rotational quantum numbers are given.

3223311321122333

2222

21113

032

021

013210 ),,( vvxvvxvvxvxvxvxvvvvvvG

ikijiiii xxx 21210

Constant (unc) (cm-1) 01 1148.3699(130)a

11x -3.8863(89) 02 513.8656(90)

22x -0.3195(34) 03 1350.2981(158)

33x -5.1985(87)

12x -3.206(10)

13x -13.760(11)

23x -4.040(10)

1 1160.7366(200)b

2 517.8043(120)b

3 1364.3966(220)b

a Uncertainties are 1 σ. b Estimated uncertainties.

SO2 EQUILIBRIUM STRUCTURE

34S16O2 Rotation-vibration interaction constants

X X v v vv e ix

ii ij

x

i ji j

( ) ( )( )1

2

1

2

1

2

x1 x2 x3 x

11 x12 x13 x22 x23 x33 x222

A B C

Xe58724.057(210) 10359.2414(800) 8805.9516(110)

α1-16.944(170) 49.1314(730) 41.186(100)

α2-1095.343(390) -2.4210(710) 15.832(120)

α3582.757(240) 34.7569(610) 31.8348(850)

γ11-1.1846(710)

γ126.0260(810) 0.3583(730)

γ13-6.0260(810) 0.1877(580) -0.7789(610)

γ2223.795(210) -0.1592(200) -0.0814(240)

γ23-16.9993(820) -0.4327(730)

γ333.4891(830)

γ2220.5281(360)

xzxzez

Aze TBBA 216 004

)(

xzxzex

Axe TBBB 2)1(8 004

)(

xzxzey

Aye TBBC 3)1(8 004

)(

)2(16

1004 xyyyxx TTTT

KJKJzzJJyyJJxx TTT ,2,2

)()2( ey

ex

ey

ex

ez BBBBB

))((2

1444

22

y

yy

x

xx

z

zzyxxy B

T

B

T

B

TBBT 2

316 zyxxzxz BBB

Corrections from centrifugal distortion terms

gIM

mI elect )(

Corrections from electron-rotation interaction effects

IFit ΔIelec ΔIcd I

IA 8.605983(31)a,b -0.00284 0.000014 8.603171(60)c

IB 48.785336(77) -0.003268 0.000961 48.783028(150)c

IC 57.390.623(76) -0.002313 -0.001641 57.386669(140)c

Moments of inertia of 34S16O2 in amu Ǻ2

These moments of inertia have been least squares fit together with those previously obtained[1] for 32S16O2 leading to the equilibrium structural parameters:

re(S=O) = 1.4307932(40) Ǻ and <e (O=S=O)= 119.32898(24)o.

[1] J.-M. Flaud and W.J. Lafferty, J. M. S. 16 (1993) 396-402

CONCLUSION

Much improved spectroscopic constants of the 34S isotopic species.

Accurate line intensities ~3% at best

Very precise equilibrium structure