The 2ν6/ν2 + ν3/ν3 + ν5 band system of CH3Br revisited: Modeling anharmonic and Coriolis interactions in a three-level system near 2000 cm-1
Abstract
The 2ν6 (A1 + E)/ν2 + ν3 (A1)/ν3 + ν5 (E) band system of CH3Br, near 2000 cm-1, has been studied, for both 79Br and 81Br isotopologues, using Fourier transform infrared spectroscopy, with a resolution of 0.003 cm-1. This band system, revealing anharmonic (Δk = Δl = 0) and Coriolis (Δk = Δl = ± 1) interactions, has been analyzed through a least-squares fit of more than 3000 transitions, for each isotopologue. More than 600 transitions belonging to the very weak ν3 + ν5 combination band were assigned for the first time, for both CH379Br and CH381Br isotopologues. Assignments of the weak 2ν60 parallel band, which is Fermi-interacting with ν2 + ν3, were also considerably extended with respect to a previous high-resolution study (Najib et al., 1985), thanks to a more accurate knowledge of the Fermi coupling parameters and of the relative positions of the interacting levels.
The least-squares fits provided quantitative reproduction of all data belonging to the four above mentioned bands. Moreover, the Coriolis coupling parameters obtained for the ν2 + ν3/ν3 + ν5 interacting bands show a remarkable consistency with those obtained for the ν2/ν5 'fundamental' system (Kwabia Tchana et al., 2004).- Publication:
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Journal of Molecular Spectroscopy
- Pub Date:
- June 2018
- DOI:
- 10.1016/j.jms.2017.05.010
- Bibcode:
- 2018JMoSp.348...79C
- Keywords:
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- Methyl bromide;
- Anharmonic;
- Coriolis and α-resonance interactions;
- Combination bands;
- High resolution;
- IR absorption