THz Spectroscopy of D2H+
Shanshan Yu, John. C. Pearson, and Takayoshi Amano Jet Propulsion Laboratory, California Institute of Technology,
Pasadena, CA 91109 USA
Copyright 2015. All rights reserved.June 25, 2015 ISMS, 2015
Generation of THz radiation
June 25, 2015 ISMS, 2015
Direct generation ; Backward-wave oscillator (BWO) < ~1.2 THz
Sideband generation of FIR lasers and microwave Saykally, Nijmegen group
Difference frequency between two IR lasers, typically CO2 lasers in 9 – 11 μm, and microwave with MIM diode “TuFIR” University of Toyama Up-conversion from low-frequency sources Commercial multiplier ( Millitech, Verginia Diode) Custom-made
Sub-millimeter to THz Spectrometer
June 25, 2015 ISMS, 2015
THz radiation sources Multiplier chain BWO
Ion generation Extended negative glow
B. J. Drouin et at, RSI. 76, 093131 (2005)J. C. Pearson et al, RSI. 82, 093105 (2011)
AMC-10 Agilent
SR830HP FG
AM/FM/TM
sync
InSborSi
pre-amp
vacuumpump
sweepsynthesizer
mm-wavemodule MMIC
ampssubmm
multipliersSample cell
detector
Functiongenerator lock-in-amplifier
PCGPIB
Examples of observed signals
June 25, 2015 ISMS, 2015
The extended negative glow discharge in a gas mixture of H2 ~ 2mTorr, D2 ~2 mTorr, and Ar ~17 mTorr, and the cell was cooled to liquid nitrogen temperature.
D2H+ as an interstellar molecule
1984 First infrared detection. ν1 fundamental band Lubic and Amano, Can. J. Phys. 62, 1886 (1984) Foster, McKellar, and Watson (1986), ν2 and ν3
Pure rotational transitions observed by high-resolution spectroscopy have been limited so far to the JKaKc = 110 -101 transition at 691.7 GHz and JKaKc =220 – 211 at 1.370 THz, and JKaKc=111 – 000 at 1.477 THz. Evenson et al, unpublished. Hirao and Amano, Astrophys. J. 597, L85 (2003) Asvany et al, Phys. Rev. Lett. 100, 233004 (2008)
June 25, 2015 ISMS, 2015
Vastel, Phillips, and Yoshida, Astrophys. J. 606, L127 (2004) Astronomical identification, 16293EB. Parise et al, A&A. 526, A31 (2012) Further confirmation of the detection
This ion plays a pivotal role in the deuterium fractionations in cold pre-stellar cores.
Laboratory Observations
June 25, 2015 ISMS, 2015
As this ion is a light asymmetric-top molecule, spectroscopic characterization and prediction of other rotational transition frequencies are not straightforward. Pure rotational lines alone are not enough to fully characterize the spectroscopic property of this light molecule.
D2H+ was generated in an extended negative glow discharge in a gas mixture of H2~ 2mTorr, D2 ~ 2 mTorr, and Ar ~17 mTorr.
The cell was cooled to liquid nitrogen temperature. Although the line density was very sparse, careful chemical checks
were carried out to ascertain that the lines observed were indeed the ones from D2H+.
Four new THz lines up to 2 THz were observed and re-measured the two out of the three known transitions.
cm-1
000
221
300 321
312
212
110
101
303
202
111
313
211
220200
100
0
Ka 2 1 0 0 1 2
ortho- para-322
Spectroscopic Analysis
June 25, 2015 ISMS, 2015
Observed data were fit to the Watson A-reduced Hamiltonian.However, to fit the data to the observed accuracy ( ~ 100 kHz), seven pure rotational line frequencies were not sufficient.
Therefore, as done in the previous analysis, combination differences derived from the three fundamental bands were fitted together with the rotational lines.
Results
June 25, 2015 ISMS, 2015
110 – 101 691660.483(20)a 1 211 – 202 1038663.154(100) -21321 – 312 1341265.342(100) 1220 – 211 1370051.6 (3)b -22111 – 000 1476605.500(15)c 0202 – 111 1572823.718(100) 3312 – 303 1654895.924(100) 5
The least squares fit was made with seven sub-mm and THz lines together with 42 combination differences derived from the IR fundamental bands.
a Amano and Hirao, J. Mol. Spectrosc., 233, 7 (2005)b Evenson et al, unpublished.c Asvany et al, Phys. Rev. Lett., 100, 233004 (2008)
A 1085215.6 (20)B 655660.0(46)C 391845.5(26)ΔJ 169.87(30)ΔJK 88.5(34)ΔK 568.46(140)δJ 63.519(79)δK 356.38(150)ΦJK 1.350(166)ΦKJ -3.56(47)ΦK 4.50(56)
Molecular constants ( in MHz )Observed transition frequenciesFrequency/MHz (o-c)/kHz
Discussion
June 25, 2015 ISMS, 2015
A 1085215.6 (20) 1085192.0 (23) 1085222.3 (114) B 655660.0(46) 655644.9 (138) 655615.5 (123) C 391845.5(26) 391843.1 (57) 391825.1 (99) ΔJ 169.87(30) 168.87(51) 167.71(47) ΔJK 88.5(34) 70.8(20) 69.3(27) ΔK 568.46(140) 579.71(177) 592.9(40) δJ 63.519(79) 63.103(192) 63.36(21) δK 356.38(150) 357.3(30) 353.5(28) ΦJK 1.350(166) ΦKJ -3.56(47) ΦK 4.50(56)
Comparison of the molecular constants ( in MHz )
Present Amano, Hiraoa Polyansky, McKellarb
a J. Mol. Spectrosc. 233, 7 (2005) b J. Chem. Phys. 92, 4039 (1990)
Prediction of the line frequencies
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Ortho-313 – 202 2947272 (15) 8.21322 – 313 2496758 (26) 9.27404 – 313 3468937 (23) 7.31
Para-212 – 101 2258673.2 (48) 5.69303 – 212 2573435.3 (95) 5.39414 – 303 3631945 (43) 8.32
Frequency/MHz α / cm-1
α; Absorption coefficient calculated by assuming μb=0.5 D and T=200 K. The spin weight is not incorporated.
4
cm-1
000
221
300 321
312
212
110
101
303
202
111
313
211
220200
100
0
Ka 2 1 0 0 1 2
ortho- para-
322
404 414
A part of this research was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.
A part of this research was supported by Natural Science and Engineering Research Council of Canada ( NSERC )
Acknowledgements
June 25, 2015 ISMS, 2015
June 25, 2015 ISMS, 2015
AMC-10 Agilent
SR830HP FG
AM/FM/TM
sync
diodeorSi
gas
pre-amp
vacuumpump
sample
sweepsynthesizer mm-wave
module MMICamps
submmmultipliers sample cell
detector
waveformgenerator lock-in-amplifier
PCGPIB
submillimeter multiplier chains with comparable power to BWOs
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