Vibrational band intensities and the electrical anharmonicity of the NH group

Abstract

The intensities of the first overtone vibration bands of the NH group in a series of complex molecules have been measured. The positions (cm -1 ) of both ν NH and 2 ν NH for many compounds containing this group have also been measured in order to obtain the mechanical anharmonicity factors. The results of the present work on the overtone bands and of previous work on the fundamental vibration bands have been correlated and interpreted in terms of mechanical and electrical anharmonicity. By making reasonable approximations and regarding the vibrating system as a diatomic molecule, numerical functions have been derived for the variation of dipole moment with bond length in the different NH compounds, and the results reveal interesting correlations with ionic character. Significantly different conclusions are reached in certain cases according to the degree of approximation used in the calculation, and comparisons of different theoretical treatments have been made.