Low Temperature Lineshape of HD 1

LOW TEMPERATURE LINESHAPE OF HYDROGEN DEUTERIDE

TF14

BRIAN J. DROUIN, HARSHAL GUPTA, JOHN C. PEARSON,

Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109-8099.

6/23/2011

Low Temperature Lineshape of HD 26/23/2011

90.7 GHz →

101.8 GHz

New THz Source for Spectroscopy

Power SpectrumUnder purged

conditions

Low Temperature Lineshape of HD 36/23/2011

Previous work is tough to best

26750252674950 2674975 2675000

Frequency (M H z)

1 0 M H z2.2 meters, 11.6 Torr

Evenson, K. M., et al. 1988, Astroph. J., 330, L135

Low Temperature Lineshape of HD 46/23/2011

Cyro-cooled cell may help

Cell designed for collisional cooling, •pathlength is 15 cm, •windows are mylar •Temperature range is 18 – 200 K

Low Temperature Lineshape of HD 56/23/2011

More than a narrower line

Cooling of the 10 Torr HD sample produced multiple effects:(1)The gas pressure decreased (of course)(2)The intensity increased(3)The Doppler width became narrower than the Lorentz width(4)The line-center shifted

2674970 2674975 2674980 2674985 2674990 2674995 26750003200

3400

3600

3800

4000

4200

4400

4600

4800

Tra

nsm

issi

on (ar

b. u

nits

)

Frequency (MHz)

1.962 Torr 1.870 Torr 1.753 Torr 1.638 Torr 1.527 Torr 1.402 Torr 1.280 Torr 1.172 Torr 1.054 Torr 0.943 Torr 0.824 Torr 0.716 Torr 0.600 Torr 0.488 Torr 0.372 Torr 0.264 Torr 0.155 Torr

0.15-1.96 Torr HD 19 K15 cm path

Low Temperature Lineshape of HD 6

HD self shift gives line center to 10 kHz

Evenson et al. 1988; 2674986.66(15)This work; 2674986.124(10)

Evenson et al. Ap.J. 1988

6/23/2011

Significant Improvement

26750252674950 2674975 2675000

Frequency (M H z)

1 0 M H z

Low Temperature Lineshape of HD 7

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.52674984.4

2674984.6

2674984.8

2674985.0

2674985.2

2674985.4

2674985.6

2674985.8

2674986.0

2674986.2

2674986.4

2674986.6

peak pick fitted Linear Fit of Frequency

Fre

quen

cy (M

Hz)

Pressure (Torr)

6/23/2011

Experiment: Evenson Ap. J. 1988 2674986.66(15) MHz

Theory: Pachuki & Komasa 2010 2674986.136(240) MHz Phys. Chem. Chem. Phys., 12, 9188.

Careful linecenter determination required

Drouin et al. 2011 (J. Mol. Struct. in press) 2674986.094(25) MHz

Low Temperature Lineshape of HD 86/23/2011

More than a narrower line – a sub-Doppler line!

Doppler halfwidth at 18 K is 2.2 MHz

Voigt function?

Only works above the minimum > 1 Torr for HD-HD broadening, lower for foreign gases

2

0 2exp)(

tkttit widthshiftv

Low Temperature Lineshape of HD 96/23/2011

2674970 2675000

10 MHz

Temperature18K, Pressures 0.05-10 Torr HD 0.5 Torr HD, 0-10 Torr pH2 or He

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Foreign Broadening Gases, p-H2 and He

0 0.5 1 1.5 2 2.5 30

0.5

1

1.5

2

2.5

3

3.5

4

f(x) = 0.0792027774395857 x

f(x) = 0.242522418712486 x

f(x) = NaN xR² = 0f(x) = NaN xR² = 0

Differential Pressure (Torr)

Diff

eren

tial L

ines

hape

(MH

z)

Pearson et al. Rev. Sci. Instr. in press 2011.

Low Temperature Lineshape of HD 10

-60

-40

-20

0

20

40

60

80

6/23/2011

Figures 9a* (pressure broadening cross section) and 9b* (pressure shift cross section) (left) ● pH2 ● nH2 broadening, ♦ ♦ He broadening (right) ● pH2 ● nH2 shift, ■ He shift

A.Schaefer J, Monchick L, “Line Broadening Of HD Immersed In He And H-2 Gas.” Astron. & Astrophys. 265, 859-868, 1992.B. Ulivi L, Lu Z, Tabisz GC, “Temperature-Dependence of The Collisional Interference In The Pure Rotational Far-Infrared Spectrum Of HD.” Phys. Rev. A, 40(2) 642-651, 1989.

Foreign Broadening Gases, Theory vs. Exp.

Low Temperature Lineshape of HD 116/23/2011

Conclusions and Future Work

ConclusionsThe linecenter of HD was better determined through ab initio calculation (until now)Planetary and Astrophysical Models can utilize calculated Broadening and Shifts if accuracy of 20-50% is OKLine narrowing parameters will be important in foreign gases

Future WorkThe three temperature points are not enough to validate a non-linear trend we have proposed extensive temperature measurementsMotional narrowing can be accommodated with sophisticated models e.g. K-S “correlated” functionals

tt

and

ttit

vvvv

widthshiftvv

2

0

1exp)()0()()(

1exp)0()(

2222

Low Temperature Lineshape of HD 126/23/2011

Acknowledgements

We would like to thank• Ed Cohen for guidance.• NASA’s Astronomy and Physics Research and

Analysis program (APRA) for funding• Herschel Science CenterAlso:• Copyright 2011 California Institute of Technology. • Government sponsorship acknowledged