Assignment and modelling of 12CH4 spectra in the 5550-5695, 5718-5725 and 5792-5814 cm-1 regions
Abstract
A new study of 12CH4 line positions and intensities was performed for the Tetradecad regions 5550,000-5695.250, 5718.8-5724.250 and 5792.36-5814.290 cm-1 using 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 squares 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 recorded in Jet Propulsion Laboratory (JPL), Pasadena, of enriched 12CH4 was used for low-J line positions. Another 80 K spectrum of enriched 13CH4 from JPL was used to discern the isotopic lines. A new measured linelist contains positions and intensities for 5819 features. Quantum assignments were made for more than 3400 transitions, which represent ∼95% of the integrated line intensity observed in this region. All assigned 3445 line positions were fitted with RMS standard deviations of 0.0024 cm-1. The sum of observed intensities between 5550 and 5695 cm-1 fell within 2% of the predicted value from ab initio variational calculations reported in the TheoReTS database (http://theorets.univ-reims.fr; http://theorets.tsu.ru).
- Publication:
-
Journal of Quantitative Spectroscopy and Radiative Transfer
- Pub Date:
- November 2018
- DOI:
- 10.1016/j.jqsrt.2018.08.006
- Bibcode:
- 2018JQSRT.219..323N
- Keywords:
-
- High resolution spectra;
- CH<SUB>4</SUB>;
- Methane;
- Tetradecad;
- Long path FTIR;
- Vibration-rotation states;
- Intensities;
- Infrared absorption;
- Effective Hamiltonian