. 1 MJ03 65 th Molecular Spectroscopy Symposium, Columbus, OH, June 2010 High Resolution Investigation of the Ethane Spectrum at 7 Micron (1430 cm -1 ) Carlo di Lauro, Franca Lattanzi Dipartimento di Chimica Farmaceutica e Tossicologia, Universita di Napoli Federico II, I Naples, Italy Keeyoon Sung, Linda R. Brown Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA Jean Vander Auwera Service de Chimie Quantique et Photophysique, Universite Libre de Bruxelles, CP 160/09, 50 avenue F.D.Roosevelt, B-1050 Brussels, Belgium Arlan W. Mantz Dept. of Physics, Astronomy and Geophysics, Connecticut College, New London, CT 06320, USA Mary Ann H. Smith Science Directorate, NASA Langley Research Center, Hampton, VA 23681, USA

. 2 MJ03 65 th Molecular Spectroscopy Symposium, Columbus, OH, June 2010 Ethane is abundant in planetary atmospheres Ethane Has 12 fundamentals but only 5 are IR active.

. 3 MJ03 65 th Molecular Spectroscopy Symposium, Columbus, OH, June 2010 New GOSAT-2009 line list in HITRAN format C 2 H 6 ν 8 Q branches are prominent in Titan: ► The spectrum of Titan at 0.5 cm –1 resolution (apodized) recorded by the CIRS FTIR on the Cassini spacecraft. ► Dotted line: calculated spectra using CH 4 ( HITRAN 2004 ) and C 2 H 6 ( based on PNNL cross sections ). ► Our goal: obtain C 2 H 6 line positions and intensities to create the first HITRAN-like database for this region.

. 4 MJ03 65 th Molecular Spectroscopy Symposium, Columbus, OH, June 2010 C 2 H 6 spectra at cold and room temperatures ► Red: room temperature Brussels 294 K (0.063 hPa, m, MOPD = 450 cm) ► Blue: cold temperature JPL 131 K (1.3 hPa, m, MOPD = 324 cm) Right: Expanded view provides direct visual indication of high J (↔) transitions and the ν 4 + ν 8 - ν 4 hot band (↑) ◊ The random strong features are from residual H 2 O inside the evacuated FTS. ↑↔ ◊ ◊ ν6ν6 ν8ν8 ν 4 +ν 12 2ν4+ν92ν4+ν9 ◊◊ ◊ ◊ ◊ ◊ ◊ ◊ ◊ ◊

. 5 MJ03 65 th Molecular Spectroscopy Symposium, Columbus, OH, June 2010 Expanding Prior Analyses of 12 C 2 H 6 States e.g. F. Lattanzi et al., J. Mol. Spectrosc. 248 (2008) ► The 7 μ m region of ethane contains four fundamentals plus two combination states and two components of an overtone. ► This results in a high density of transitions involving rotation-torsion structure, further complicated by hot bands arising from the ν 4 state at 289 cm -1. Vib. Band Type & Vib Sym Center (cm -1 ) ν 4 +ν 12 ┴ IR E u ν8ν8 ┴ IR E u ν 11 Raman E g ν4 6ν4 Raman E 3s Raman E 3d ν2ν2 Raman A 1g ν4+ν92ν4+ν9 ┴ IR E u 1388 ν6ν6 ║ IR A 1u

. 6 MJ03 65 th Molecular Spectroscopy Symposium, Columbus, OH, June 2010 Experimental Details: high resolution FTIR FTS and Gas conditionsJPL: Cold Temp Bruker 125 HR Brussels: Room Temp Bruker 120 HR Light SourceGlower Beam SplitterKBr DetectorMCT Resolution (unapodized) cm cm -1 Normal SamplesC2H6C2H6 C2H6C2H6 Sample Pressure (hPa) , 0.11, 0.30 Path length (cm) Temperature (K)131, Useable Band Pass (cm -1 )1240 – Calibration StandardsResidual H 2 O N 2 O Position precisions cm -1 Over positions from room temperature data

. 7 MJ03 65 th Molecular Spectroscopy Symposium, Columbus, OH, June 2010 ► Upper left: One hot band ν 4 + ν 8 - ν 4 easily identified ► Lower left: level crossings at high J create band head in P Q 1 ► Right panels: O- and S-type forbidden lines New modeling permitted further assignments of greatly perturbed Q branches of ν 8 !

. 8 MJ03 65 th Molecular Spectroscopy Symposium, Columbus, OH, June 2010 ► R-lines of ν 8, with two perturbation-activated t-transitions to ν 6 with ΔK=3 (underlined and marked by a star). ► ↔ anomalous J- pattern of r Q 16 and its eventual turn is caused by the same interaction, with K=19 in ν 6 and 17 in ν 8. New assignments at much higher J ↔ cm -1..

. 9 MJ03 65 th Molecular Spectroscopy Symposium, Columbus, OH, June 2010 ► arises from nearly constant torsional splitting and K-splitting (increasing with J). ► the (–l), K=2 levels are split by the l(2,–1) interaction with the (+l), K=1 levels [also affected by l(2,2)-doubling]. ► The split components K± correspond to upper state wavefunctions √2 (Ψ JKl ± Ψ J–K–l ) with K=2 and l = –1. p Q 3 of ν 8 split into 4 components by interaction ► K- components: marked above spectrum ► K+ components: marked below spectrum ►The J-spacing decreases with increasing J leading to a bandhead in the K– subset. (h = hot transition, w = water line).

. 10 MJ03 65 th Molecular Spectroscopy Symposium, Columbus, OH, June 2010 ► left: level crossings between ν 8 and ν 6 ► right: no transitions of 3-quanta band assigned (yet) Interaction schemes at higher K

. 11 MJ03 65 th Molecular Spectroscopy Symposium, Columbus, OH, June 2010 Effects of perturbation on rotational constant B ►The strong perturbation within ν 8 levels is illustrated using the effective rotational constants B, as determined from ν 8 transitions. ► These points should fall on one smoothly varying line. ► The values for levels linked by the l (2,–1) interaction (connected by straight lines) show opposite deviations from the patterns at high | Kl |. Effective B-values for ν 8

. 12 MJ03 65 th Molecular Spectroscopy Symposium, Columbus, OH, June 2010 Global Hamiltonian (so far) Vibs. ν6ν6 ν8ν8 ν 4 +ν 12 2ν4+ν92ν4+ν9 ν6ν6 E CC ν8ν8 C E l(2,2) F l(2,-1) ν 4 +ν 12 F l(2,-1) E l(2,-1) l(2,2) 2ν4+ν92ν4+ν9 Cl(2,-1) E l(2,2)

. 13 MJ03 65 th Molecular Spectroscopy Symposium, Columbus, OH, June 2010 Assigned IR lines of C 2 H 6 at 7 microns Bandcm -1 K maxJ maxAssigned ΔK=-2ΔK=+2ΔK=3 ν 4 +ν ν8ν ν4+ν92ν4+ν ? ν6ν ν 4 +ν 8 - ν rms cm -1 Cold bands: rms cm -1 Hot band

. 14 MJ03 65 th Molecular Spectroscopy Symposium, Columbus, OH, June 2010 Calculated vs observed ethane spectra ► Red: observed at 294 K (0.065 hPa) ► Blue: predicted ν 8, ν 6, ν 4 + ν 12 ► green: hot band: ν 4 + ν 8 - ν 4 The random strong features are residual H 2 O inside the evacuated FTS. ►transitions moments: ν 8 and ν 6 from selected line intensities, ν 4 + ν 12 (solely from borrowing) ν 4 + ν 8 - ν 4 Boltzmann scaling ► Preliminary linelist will have some calculated positions replaced with observed line centers. ► Line intensities (still in progress).

. 15 MJ03 65 th Molecular Spectroscopy Symposium, Columbus, OH, June 2010 Importance of ethane isotopologues

. 16 MJ03 65 th Molecular Spectroscopy Symposium, Columbus, OH, June 2010 CONCLUSION These new linelists with lower states energies ► Characterize the line-by-line spectrum ► Improve molecular databases for planetary remote sensing Future work ► Additional experimental efforts and theoretical analyses to understand the whole spectrum and provide reliable prediction of molecular line parameters for remote sensing of planetary atmospheres. ► This study is one important step toward this ultimate goal. JVDA acknowledges financial support from the Fonds de la Recherche Scientifique (FRS-FNRS, Belgium, contracts FRFC and IISN), and the Actionde Recherches Concertées of the Communauté française de Belgique. Part of the research described in this paper was performed at the Jet Propulsion Laboratory, California Institute of Technology, Connecticut College, and NASA Langley under contracts and grants with the National Aeronautics and Space Administration.

. 17 MJ03 65 th Molecular Spectroscopy Symposium, Columbus, OH, June 2010 Interaction at low K-values. ► Fermi resonance of ν 8 and ν 4 + ν 12, shown for +l. ► l(2,-1) resonance within ν 8, dashed lines; shown for those pairs where lines with ΔK=±2. The mechanism by which the l (2,2) splitting of K=1,+l is transmitted (by l(2,-1) resonance to K=2,-l, (in P Q 3 ). ► x,y-Coriolis coupling of ν 6 and 2 ν 4 + ν 9 : large torsional splitting (~ 3 cm -1 ) causes a detectable splitting in ν 6 for K= 3, 4, 5.