CH stretching vibrations of pyrazole and of its deuterated species. Anharmonicity of modes and molecular pseudo‐symmetry

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Abstract
The three ν(CH or CD) fundamentals of pyrazole‐D0 (1a) of its deuterated NH species, −4‐D1 (2a), −3,5‐D2 (3a), −3,4,5‐D3 (4a), and ND species, −1‐D1 (1b), −1,4‐D2 (2b), −1,3,5‐D3 (3b), ‐D4 (4b), were obtained by Raman spectroscopy. Each a, b couple (i.e. 1a, 1b, etc.) gives identical ν(CH or CD) bands. One band originates essentially in the stretching of the atom (H or D) in position 4. Two other bands originate essentially in the stretching movements of the atoms in positions 3 and 5. The relation of infrared to Raman intensity, the relative intensity of bands in infrared, the relative position of bands, the application of isotropic rules and the determination of mode anharmonicity constants provide a C2ν‐like image of these Cs‐symmetrical molecules.