Temperature dependence of the absorption spectrum of CH4 by high resolution spectroscopy at 81 K: (II) The icosad region (1.49–1.30 µm)

Alain Campargue (1, 2) , W. Le (1, 3) , Samir Kassi (1, 2) , Milan Masat (4) , Ondřej Votava (4)

1 LSP - Laboratoire de Spectrométrie Physique
2 LAME-LIPhy - LAsers, Molécules et Environnement
3 LIPhy - Laboratoire Interdisciplinaire de Physique [Saint Martin d’Hères]
4 IPC - J. Heyrosky´ Institute of Physical Chemistry

The high resolution absorption spectrum of methane has been recorded at liquid nitrogen temperature by differential absorption spectroscopy between 6717 and 7351 cm1 (1.49–1.36 mm) using a cryogenic cell and a series of distributed feed back (DFB) diode lasers. The investigated spectral region corresponds to the very congested low energy part of the icosad for which the HITRAN database provides neither rovibrational assignments nor the lower state energies. The positions and strengths at 81 K of 9389 transitions were obtained from the spectrum analysis. The minimum value of the measured line intensities (at 81 K) is on the order of 1026cm/molecule. From the variation of the line strength between 81 K and 296 K, the low energy values of a total of 4646 transitions were determined. They represent 79.4% and 68.4% of the total absorbance in the region at 81 and 296 K, respectively, and include 28 transitions assigned to the n2+4n4 band near 6765 cm1. The reliability of the method based on the association of lines with coinciding centers in the 81 K and 296 K spectra is discussed. The results of the present analysis have been combined with previously analyzed high energy part of the icosad dominated by the n2+2n3 band near 7510 cm1. The line list for the whole icosad (6717–7655cm1) consists of 12 865 transitions at 81 K.

Mots clés: Methane; CH4; Absorption spectroscopy; HITRAN; Titan

Domaines: Physique Atomique [physics.atom-ph]; Optique [physics.optics]

Alain Campargue, W. Le, Samir Kassi, Milan Masat, Ondřej Votava. Temperature dependence of the absorption spectrum of CH4 by high resolution spectroscopy at 81 K: (II) The icosad region (1.49–1.30 µm). Journal of Quantitative Spectroscopy and Radiative Transfer, 2010, 111 (9), pp.1141-1151. ⟨10.1016/j.jqsrt.2009.11.025⟩. ⟨hal-00562613⟩