A program for determining primitive semiclassical eigenvalues for vibrating/rotating nonlinear triatomic molecules

This paper presents the theoretical details of the fast Fourier transform method for determining semiclassical eigenvalues in vibrating/rotating triatomic molecules. Much of this is concerned with transformations between space fixed Cartesian coordinates and momenta, normal coordinates and momenta and symmetric top rotational action/angle variables. Applications of the method to both rigid and vibrating H₂O in both the ground and j = 3 rotational states are presented. Comparison with experiment indicates that errors of a few cm^-1 are typical.