Large scale variational calculations for the vibrational states of HOCl are
performed using a recently developed, accurate nb initio potential energy
surface. Three different approaches for obtaining vibrational states are em
ployed and contrasted; a truncation/recoupling scheme with direct diagonali
zation, the Lanczos method, and Chebyshev iteration with filter diagonaliza
tion. The complete spectrum of bound states for nonrotating HOCl is compute
d and analyzed within a random matrix theory framework. This analysis indic
ates almost entirely regular dynamics with only a small degree of chaos. Th
e nearly regular spectral structure allows us to make assignments for the m
ost significant part of the spectrum, based on analysis of coordinate expec
tation values and eigenfunctions. Ground state dipole moments and dipole tr
ansition probabilities are also calculated using accurate ab initio data. C
omputed values are in good agreement with available experimental data. Some
exact rovibrational calculations for J = 1, including Coriolis coupling, a
re performed. The exact results are nearly identical with those obtained fr
om the adiabatic rotation approximation and very close to those from the ce
ntrifugal sudden approximation, thus indicating a very small degree of asym
metry and Coriolis coupling for the HOCl molecule. (C) 1998 American Instit
ute of Physics. [S0021-9606(98)00947-7].