Discrete variable representations of large-amplitude ro-vibrational states in a generalised coordinate system

We present a formulation of the triatomic ro-vibrational nuclear motion problem in a set of generalised coordinates using a discrete variable representation (DVR). These coordinates are expressed in terms of two distances and an included angle, and contain many well known coordinate systems. Applications to LiCN, Na3 and H+3 which illustrate the power of the method are described. The resulting energy levels and wavefunctions are discussed. Our Na3 fundamental frequencies are found to be in good agreement with experiment.