The calculation of the vibration-rotation energies of triatomic molecules using scattering coordinates

Abstract

Department of Physics and Astronomy, University College London, Gower Street, London WCIE 6BT, England Received 25 January 1986 This paper is a review of work I have been involved with concerning the calculation of ro-vibrational energy levels and wavefunctions, mainly of triatomic systems. The method reviewed is that of Tennyson and Sutcliffe for the calculation of spectra of triatomics as atom-diatom collision complexes, which is particularly ap- propriate for molecules with one or more large amplitude vibrational mode. The method uses polynomial basis functions to carry the nuclear motions and is variational for a given potential. Hamiltonians for four different sets of body-fixed axes are derived. The computational implementation of the method is discussed, including improvements to some published algorithms. The use of a two step (secondary) variational procedure for highly-excited rotational states is discussed and sample results given. Extensions to non-Born-Oppenheimer problems, transition intensities and polyatomic molecules are also considered. Comparisons are made with other techniques for calculating ro-vibrational spectra with some specific molecular examples.