Measurements and modeling of long-path 12CH4 spectra in the 5300–5550 cm−1 region

• Published in: Journal of quantitative spectroscopy & radiative transfer Vol. 202; pp. 255 - 264
• Main Authors: Nikitin, A.V., Thomas, X., Daumont, L., Rey, M., Sung, K., Toon, G.C., Smith, M.A.H., Mantz, A.W., Tashkun, S.A., Tyuterev, Vl.G.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.11.2017
• Subjects: CH4; Effective Hamiltonian; High resolution spectra; Infrared absorption; Intensities; Long path FTIR; Methane; Tetradecad; Vibration-rotation states; Methane; Intensities; Effective Hamiltonian; High resolution spectra; Infrared absorption; Tetradecad; CH4; Long path FTIR; Vibration-rotation states
• ISSN: 0022-4073; 1879-1352
• DOI: 10.1016/j.jqsrt.2017.07.030

•5934 line positions and intensities were retrieved in the 5300–5550 cm−1 region.•12CH4 line list with assignments was made in the 5300–5550 cm−1 region.•2847 experimental line positions were modeled to 0.0025 cm−1.•2227 experimental line intensities at 296 K were modeled to 8.6% rms. A new study of 12CH4 line positions and intensities was performed for part of the Tetradecad region between 5300 and 5550 cm−1 using four long path (202 m, 602 m, 1604 m and 1804 m) spectra of normal samples of CH4 at different pressures recorded with a Fourier transform spectrometer in Reims, France. Line positions and intensities were retrieved by least square curve-fitting procedures and analyzed using the effective Hamiltonian and the effective dipole moment expressed in terms of irreducible tensor operators adapted to spherical top molecules. An 80 K spectrum from JPL of enriched 12CH4 was used for low-J line positions. One other 80 K spectrum from JPL of enriched 13CH4 was used to discern the isotopic lines. A new measured linelist contains positions and intensities for 5934 features. Quantum assignments were made for 2847 transitions, which represent ∼90% of the integrated line intensity observed in this region. All assigned line positions and 2227 selected line intensities were fitted with RMS standard deviations of 0.0025 cm−1 and 8.6%, respectively. The sum of observed intensities between 5300 and 5550 cm−1 fell within 2% of the predicted value from ab initio variational calculations.