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

tamano@jpl.nasa.gov

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 Evenson et al, unpublished.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