ELECTRIC ANHARMONICITY IN XY3 PYRAMIDAL MOLECULES - DIPOLE-MOMENT FUNCTION OF (NH3)-N-14 AND (NH3)-N-15

This paper is concerned with the determination of the shape of the electric dipole moment function of a pyramidal XY3 molecule with a low barrier to inversion over a wide range of values for the inversion coordinate. The effective inversion-rotation Hamiltonian [V. Špirko, J. M. R. Stone, and D. Papoušek, J. Mol. Spectrosc. 60, 159-178 (1976)] is used to explain the anomalous vibrational dependence of the electric dipole moment of 14NH3 [F. Shimizu, J. Chem. Phys. 52, 3572-3576 (1970)], and of 15NH3 [B. J. Orr and Takeshi Oka, J. Mol. Spectrosc. 66, 302-313 (1977)]. The experimental data of Orr and Oka are used to fit the μz component of the total dipole moment function and the fitted function is used to predict the transition moments in the nν2 inversion sequence of 14NH3 and 15NH3. To illustrate the measure of the rotational dependence of the transition moments, two examples, involving ground and excited (v2 = 1) states, are also presented. © 1979.