Laboratory studies of methane near 2 μ m

Details Laboratory studies of methane near 2 μ m Laboratory studies of methane near 2 μ m

Dec 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000dps....32.6535r&link_type=abstract

American Astronomical Society, DPS Meeting #32, #65.35; Bulletin of the American Astronomical Society, Vol. 32, p.1646

Astronomy and Astrophysics

Astronomy

Scientific paper

The 2 μ m region is a ``window" region for planets and stars abundant in methane. Characterizing the methane absorptions requires that a large number of vibration-rotation states be studied. The rovibrational levels in methane are grouped in vibrational polyads. The absorption from the three first polyads of methane (ground state: <= 10 μ m, dyad: 5--10 μ m, pentad: 3--5 μ m) are well understood and can be predicted using quantum mechanical models. Two higher polyads must be modeled to describe the 2 μ m window. The polyad called the octad has eight vibrational states in the 2--3 μ m interval. The next polyad (tetradecad) observed in the range 1.6--2 μ m is composed of 14 vibrational levels. The analyses of these two polyads have been undertaken at Dijon using high--quality FTIR spectra recorded at Kitt Peak National Observatory. The analysis of the octad was helped by spectra of the Q-branch regions of the 3ν 4 and ν2+2ν4 bands recorded at 80 K at NIST. The theoretical background for modeling rovibrational energy levels and corresponding transitions has been developed at Dijon. The analysis of the COMPLETE octad was performed for J <= 16 with a Hamiltonian containing 253 adjustable parameters (for 8 bands and 24 subbands). Nearly 8000 lines in the octad were assigned and reproduced with a standard deviation of 0.044 cm-1. Intensities were also modeled to 16% for some 2500 transitions. A prediction of some 57000 methane transitions in HITRAN format is available (from Brown). The analysis of the tetradecad system led to the assignment of nearly 200 lines of 4ν 4 band around 1.9 μ m, yielding a standard deviation of 0.180 cm-1, and to nearly 300 lines of 2ν 2+ν_3 around 1.7 μ m, yielding a standard deviation of 0.270 cm-1. Intensities are being measured. The spectral simulation is in progress near 1.8 μ m where maximum complication occurs. Part of the research reported in this paper was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration

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