A joint local mode and normal mode interpretation of vibrational anharmonicity in methyl bromide |
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| Institution: | 1. Institute of Coordination Bond Metrology and Engineering, College of Materials Science and Engineering, China Jiliang University, Hangzhou 310018, China;2. Key Laboratory of Low-Dimensional Materials and Application Technology (Ministry of Education) and School of Materials Science and Engineering, Xiangtan University, Hunan 411105, China;3. Institute of Nanosurface Science and Engineering, Shenzhen University, Shenzhen 518060, China;4. NOVITAS, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore;1. Key Laboratory of Low-dimensional Materials and Application Technology (MOE) and School of Materials Science and Engineering, Xiangtan University, Xiangtan 411105, China;2. Institute of Coordination Bond Metrology and Engineering, College of Materials Science and Engineering, China Jiliang University, Hangzhou 310018, China;3. Institute of Nanosurface Science and Engineering, Shenzhen University, Shenzhen 518060, China;4. NOVITAS, School of EEE, Nanyang Technological University, Singapore 639798 |
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| Abstract: | The gas-phase i.r. spectrum of CH3Br has been studied up to 14 000 cm?1. Some 32 new vibration levels are located accurately, involving up to 5 quanta (V= 5) of excitation in CH stretching. Reproduction of a total of 72 vibration levels is achieved through a joint treatment of CH stretching vibrations in a local mode basis, other vibrations in a normal mode basis, and with the inclusion of two Fermi resonances. The local mode approach satisfactorily accounts for the effects of the large Darling—Dennison vibrational interactions which occur between CH stretching modes. Fermi resonances between CH stretching and overtones of both methyl group deformation vibrations (ν2 and ν5) are treated explicitly. Interacting levels become quasi-degenerate at V = 3 in the case of 2ν5, and at V = 5 in the case of 2ν2. The analysis permits the determination of a complete set of 27 physically representative anharmonicity constants for CH3Br, four of which are interrelated through the local mode model. Data reproduction between 600 and 14 000 cm?1 is achieved with an r.m.s. error of 2.55 cm?1. |
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