CALCULATIONS OF ROVIBRATIONAL SPECTRA OF WATER BY MEANS OF PARTICLES-ON-CONCENTRIC-SPHERES MODELS
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Date
1984
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Publisher
Ohio State University
Abstract
Two versions of the adiabatic approach equivalent for states with an equal number of quanta in local stretching modes have been suggested for calculations of rovibrational levels of water. If the two modes are not equally populated there exist two possibilities: to treat symmetric or antisymmetric stretching wave functions as either nondegenerate or quasidegenerate. The first possibility leads to the equation for two particles rotating on a sphere. The second case yields a set of two coupled differential equations. Decoupling the set in the zeroth order approximation results in the equation for two particles rotating on different spheres. It has been shown that the particle-on-concentric-spheres (POCS) model allows one to describe both bending frequencies and rotational structure of the ground and some excited vibrational states, with accuracy adequate for spectroscopic predictions. If the radius of the sphere is chosen to coincide with the equilibrium bond length the potential function turns out to be exactly the same as for the rigid bender model. However the modification of the kinetic energy suggested here results in a better agreement between approximate and accurate values of rotational frequencies in the ground and excited bending states for both $H_{2}O$ and $D_{2}O$. Compared with the rigid bender model, this modification gives slightly better, approximately the same and slightly worse results for bending frequencies of $H_{2}O, D_{2}O$ and $T_{2}O$ respectively.
Description
Author Institution: Department of Chemistry, The University of Chicago; Department of Chemistry, Cornell University; Institute de Estructura de la Materia, C.S.I.C., Serrano