A VARIATIONAL PROCEDURE FOR CALCULATION OF THE RO-VIBRATIONAL ENERGY-LEVELS OF TRIATOMIC-MOLECULES USING TRANSFORMED INTERNAL COORDINATES

In this paper, we present a two-step variational procedure to solve th e ro-vibrational problems for triatomic molecules using the transforme d internal valence coordinates. The first step is the solution of a se ries of secular problems depending on K, which is the projection of th e total angular momentum onto the body-fixed z-axis. In the second ste p, we have used the N lowest eigenfunctions obtained in the first step to construct the rovibrational Hamiltonian matrix and suggested an ef ficient diagonalization method to diagonalize this matrix. The re-vibr ational energy levels of the H2O molecule for J less than or equal to 20 on the potential energy function fitted by Jensen have been calcula ted and compared with the observed values and some theoretical results to test the procedure.