New analysis of the Coriolis-interacting v2 and v5 bands of CH3Br and CH3Br |
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Authors: | F Kwabia Tchana I Kleiner N Lacome |
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Institution: | a Laboratoire de Photophysique Moléculaire, Bât. 350, 91405 Orsay Cedex, France b Laboratoire de Dynamique, Interactions et Réactivité, Université Pierre et Marie Curie, UMR CNRS 7075, Case Courrier 49, 4 Place Jussieu, 75252 Paris Cedex 05, France c Faculté des Sciences, Université de Ngaoundéré, B.P. 454 Ngaoundéré, Cameroon d Centre de Physique Atomique Moléculaire et Optique Quantique (CEPAMOQ), Université de Douala, B.P. 8580 Douala, Cameroon |
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Abstract: | The and fundamental bands of CH379Br and CH381Br have been studied by Fourier transform infrared spectroscopy with an unapodized resolution of 0.004 cm−1, corresponding to an improvement of one order of magnitude compared to previous studies. For both isotopomers, some 2427 (2239) lines were newly assigned for the parallel and the perpendicular bands and, in addition, 80 perturbation-allowed transitions were also added. The ground-state axial rotational constants A0 were redetermined from allowed and perturbation-allowed infrared transitions observed in the v2 and v5 bands around the local crossing. The A0 values obtained for both isotopomers are more accurate but fully compatible with those obtained previously. Using those results, and the variation of the rotational constants with vibration, new accurate equilibrium constants Ae and Be have been also determined for CH379Br and CH381Br. The excited states v2=1 and v5=1 are coupled by Coriolis-type interactions (Δl=±1,ΔK=±1) and (Δl=?1,ΔK=±2), while the l5=±1 levels of v5 interact also through “l(2,2)”-type interaction (Δl=±2,ΔK=±2). The Coriolis coupling term was determined to be for CH379Br and for CH381Br. All interaction parameters have been determined with higher accuracy, compared to previous studies. A total of 4213 (3704) line positions with J?68(64) and K?16(11) including all available data was fitted using 20 (18) parameters with a root-mean-square deviation of 0.0007 (0.0006) cm−1 for CH379Br and CH381Br, respectively. Two different but equivalent forms of reduced Hamiltonians with two different sets of constrained constants were successfully applied according to Lobodenko's reduction J. Mol. Spectrosc. 126 (1987) 159]. The ratio of the transition moments, |d2/d5|=1.65, and a positive sign of the Coriolis intensity perturbation d2×ζ25×d5 were determined. Therefore, it has been possible to generate an accurate prediction of the whole spectrum between 1200 and 1650 cm−1, including Q branches. |
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Keywords: | Methyl bromide Coriolis interaction Resonance High resolution IR absorption |
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