The watson U( ρ) term in the one-dimensional Semirigid Bender Hamiltonian for the HF dimer

Abstract

We have recalculated the minimum energy path for the trans-bending tunneling motion of the HF dimer using mass-scaled Cartesian coordinates, and have set up the appropriate Semirigid Bender wave equation. Using Hougen-Bunker-Johns axes that keep I xρ; = 0, we can calculate the full Watson U( ρ) term as a function of the tunneling coordinate ρ. The rapid change in the magnitude of R ab (the distance between the centers of mass of the two HF fragments), along the minimum energy trans-tunneling path, causes U( ρ) to become very large in the vicinity of the equilibrium structure. For the calculation of the K-type rotation and trans-tunneling energies it is possible to set up a one-dimensional model Hamiltonian, as we did previously, by neglecting the variation of R ab with ρ. We do this in an optimization of the minimum energy path to the currently available term values in order to obtain an effective minimum energy path and predicted term values.