VARIATIONAL CALCULATIONS OF ROVIBRATIONAL ENERGY-LEVELS AND TRANSITION INTENSITIES FOR TETRATOMIC MOLECULES

A description is given of an algorithm for computing rovibrational ene rgy levels for tetratomic molecules. The expressions required for eval uating transition intensities are also given. The variational principl e is used to determine the energy levels, and the kinetic energy opera tor is simple and evaluated exactly. The computational procedure is sp lit up into the determination of one-dimensional radial basis function s, the computation of a contracted rotational-bending basis, followed by a final variational step coupling all degrees of freedom. An angula r basis is proposed whereby the rotational-bending contraction takes p lace in three steps. Angular matrix elements of the potential are eval uated by expansion in terms of a suitable basis, and the angular integ rals are given in a factorized form which simplifies their evaluation. The basis functions in the final variational step have the full permu tation symmetries of the identical particles. Sample results are given for HCCH and BH3.