Line Positions and Intensities for the 12 Band

Line Positions and Intensities for the ν 12 Band of 13 C 12 CH 6 V. Malathy Devi 1, D. Chris Benner 1, Keeyoon Sung 2, Timothy J. Crawford 2, Arlan W. Mantz 3, and Mary Ann H. Smith 4 1 The College of William and Mary, Williamsburg, VA 23187, U. S. A. 2 Science Division, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, U. S. A. 3 Dept. of Physics, Astronomy and Geophysics, Connecticut College, New London, CT 06320, U. S. A. 4 Science Directorate, NASA Langley Research Center, Hampton, VA 23681, U. S. A. FE 08 -69 th International Symposium on Molecular Spectroscopy, June 16 -20, 2014 1

Ethane in Earth and Planetary Atmospheres The most abundant ethane isotopologue, 12 C 2 H 6, is easily detected in spectra of Earth and planetary atmospheres and in comet volatiles. § 13 C 12 CH 6 appears in atmospheric spectra of Jupiter, Saturn, Neptune and Titan. § Spectral observations of both isotopologues at 12 µm enable 13 C/12 C ratios to be determined for Jupiter, Saturn, and Titan. Recent high-resolution studies to improve 12 -µm ethane parameters: 12 C 2 H 6 ν 9 band [Malathy Devi et al. , JQSRT 111 (2010) 1234 -1251; Malathy Devi et al. , JQSRT 111 (2010) 2481 -2504 and references therein] updated in HITRAN 2012. 13 C 12 CH ν 12 based on Kurtz et al. (1991) and Weber et al. (1993, 1994) in GEISA 2009 ; more recent ν 12 and ν 12+ν 6−ν 6 positions and assignments [Borvayeh et al. , J. Mol. Spectrosc. 255 (2009) 157 -163; Moazzen-Ahmadi et al. , JQSRT 129 (2013) 316 -323] not yet in GEISA or HITRAN. 6 Using low-temperature spectra to minimize hot-band transitions, we have measured line positions and absolute intensities for 1660 ν 12 transitions. FE 08 -69 th International Symposium on Molecular Spectroscopy, June 16 -20, 2014 2

13 C 12 CH 6 in the spectrum of Jupiter P. V. Sada, G. H. Mc. Cabe, G. L. Bjoraker, D. E. Jennings, D. C. Reuter. Astrophys. J. 472 (1996) 903 -907. FE 08 -69 th International Symposium on Molecular Spectroscopy, June 16 -20, 2014 3

Recording the Spectra § The spectra of 13 C 12 CH 6 were recorded with the 20. 38 cm coolable cell [Sung et al. , J. Mol. Spectrosc. 262 (2010) 122 -134] installed inside the sample compartment of the Bruker IFS 125 HR spectrometer at JPL. The cell body is oxygen free high conductivity (OFHC) copper with wedged Zn. Se windows; the vacuum shroud box has wedged KBr windows. • KBr beamsplitter, MCT detector, resolution ~0. 003 cm-1 • Temperatures: 130 K, 178 K, 208 K, and 294 K. • Total pressures: 2 – 5 torr (2. 7 – 6. 7 h. Pa) at 130 – 208 K; 9. 5 torr (12. 6 h. Pa) at 294 K. • Gas sample: 13 C-enriched ethane (13 C, 99%) from Cambridge Isotope Labs. FE 08 -69 th International Symposium on Molecular Spectroscopy, June 16 -20, 2014 4

Laboratory spectra of 13 C 12 CH 6 at two temperatures a 1 atm = 101. 3 k. Pa = 760 Torr FE 08 -69 th International Symposium on Molecular Spectroscopy, June 16 -20, 2014 5

Laboratory spectra of 13 C 12 CH 6 at two temperatures RQ(J, 7) RQ(J, 8) ● RR(5, 4) a ● RR(6, 5) 1 atm = 101. 3 k. Pa = 760 Torr FE 08 -69 th International Symposium on Molecular Spectroscopy, June 16 -20, 2014 6

Multispectrum Fitting Analysis § Only the 4 low-temperature spectra 130– 208 K were included in the fits to minimize interferences from weak high-J and hot-band transitions. Short spectral intervals (1‒ 3 cm− 1) were fit in all 4 spectra simultaneously. § Important: All spectra are calibrated to the same reference standard (H 2 O ν 2 line positions [R. A. Toth, J. Opt. Soc. Am. B 8 (1991) 2236 -2255]). § Initially 13 C 12 CH 6 line list from GEISA 2009 (also available as a supplement to HITRAN 2008). Weak features missing from the original list were added interactively. § HITRAN partition functions [A. L. Laraia et al. , Icarus 215 (2011) 391 -400] were applied in the fitting algorithm to obtain corresponding line intensities at 296 K. § Intensity ratios of torsionally split components and their separations, were at first constrained to predicted values, but some were later adjusted in the fitting process. § Lorentz half-width, pressure-induced shift coefficients and their temperature dependences were fixed to appropriate default values using 12 C 2 H 6 measured values [Malathy Devi et al. , JQSRT 111 (2010) 1234 -1251; JQSRT 111 (2010) 2481 -2504]. FE 08 -69 th International Symposium on Molecular Spectroscopy, June 16 -20, 2014 7

Observed torsional splitting in ν 12 of 13 C 12 CH FE 08 -69 th International Symposium on Molecular Spectroscopy, June 16 -20, 2014 6, 2 Torr at 130 K 8

13 C 12 CH 6 multispectrum fit and residuals 4 self-broadened spectra The same color codes are used for the observed spectra and residuals: Red Blue Green Black PP (2. 05 Torr at 130 K) (4. 99 Torr at 178 K) (2. 95 Torr at 178 K) (4. 94 Torr at 208 K) transitions Torsional splitting not resolved FE 08 -69 th International Symposium on Molecular Spectroscopy, June 16 -20, 2014 9

13 C 12 CH 6 multispectrum fit and residuals 4 self-broadened spectra The same color codes are used for the observed spectra and residuals: Red (2. 05 Torr at 130 K) Blue (4. 99 Torr at 178 K) Green (2. 95 Torr at 178 K) Black (4. 94 Torr at 208 K) PP, RP, and PQ transitions Torsional splitting not resolved FE 08 -69 th International Symposium on Molecular Spectroscopy, June 16 -20, 2014 10

13 C 12 CH 6 multispectrum fit and residuals 4 self-broadened spectra The same color codes are used for the observed spectra and residuals: Red Blue Green Black (2. 05 Torr at 130 K) (4. 99 Torr at 178 K) (2. 95 Torr at 178 K) (4. 94 Torr at 208 K) PP, RP, and PQ transitions Torsional splitting is resolved for high-J PQ(K=6) lines FE 08 -69 th International Symposium on Molecular Spectroscopy, June 16 -20, 2014 11

13 C 12 CH 6 multispectrum fit and residuals 4 self-broadened spectra The same color codes are used for the observed spectra and residuals: Red Blue Green Black PR (2. 05 Torr at 130 K) (4. 99 Torr at 178 K) (2. 95 Torr at 178 K) (4. 94 Torr at 208 K) and RR transitions Torsional splitting is resolved only for PR(18, 6) line ~830. 1 cm-1 FE 08 -69 th International Symposium on Molecular Spectroscopy, June 16 -20, 2014 12

Results Four spectra recorded at 130 to 208 K were included in the analysis. Of the 2948 spectral lines measured, 34% were weak, unidentified features; however, approximate lower state energies could be estimated for some of these lines. 15% of the remaining ν 12 transitions were not reported because of blends or unsatisfactory fits. Line positions and intensities are reported for 1660 ν 12 transitions of 13 C 12 CH with known assignments. 6 • Positions accurate to ± 1 to 4 × 10− 4 cm− 1 • Intensities accurate to ± 2 to 3% Good agreement with HITRAN 2008, but not HITRAN 2012. [13 C 12 CH 6 intensities in HITRAN 2012 were inadvertently re-scaled by the same factor (− 15%) as those for 12 C 2 H 6. ] FE 08 -69 th International Symposium on Molecular Spectroscopy, June 16 -20, 2014 13

13 C 12 CH ν 12 Positions and Intensities Compared to HITRAN 08 Supplement (same as GEISA 09) 6 Most position differences are within ± 0. 0005 cm− 1 PS/HITRAN 08 intensity ratio Mean ± Standard Deviation: 1. 09 ± 0. 10 To agree with the present study, the 13 C 12 CH ν intensities 6 12 in HITRAN 2012 should be scaled by 1. 28 FE 08 -69 th International Symposium on Molecular Spectroscopy, June 16 -20, 2014 14

Summary From multispectrum fits of low-temperature (130 – 208 K) spectra we have determined • Line positions and absolute intensities for 1660 ν 12 transitions of 12 C 13 CH 6. • Positions and intensities for approximately 1000 other unassigned lines in the 12. 2 µm region. • Approximate lower state energies for some of these unassigned lines. Results were recently published: V. Malathy Devi et al. , J. Mol. Spectrosc. 301 (2014) 28 -38. http: //dx. doi. org/10. 1016/j. jms. 2014. 05. 005 FE 08 -69 th International Symposium on Molecular Spectroscopy, June 16 -20, 2014 15

The Team and Acknowledgements Malathy Keeyoon Linda Tim Arlan Mary Ann Chris Acknowledgements Research described in this talk was performed at Connecticut College, the College of William and Mary, NASA Langley Research Center and the Jet Propulsion Laboratory, California Institute of Technology, under contracts and cooperative agreements with the National Aeronautics and Space Administration. We thank Linda Brown for technical assistance and helpful comments. FE 08 -69 th International Symposium on Molecular Spectroscopy, June 16 -20, 2014 16