Rotationally inelastic scattering and potential calculation for NH3+He

Abstract

In a crossed molecular beam experiment, time-of-flight distributions of NH3 molecules scattered from He have been measured as a function of the deflection angle at E=97.7 meV. The spectra, which cover a center-of-mass angular range from 97° to 168° show appreciable rotational energy transfer in the backward direction. These data, which are sensitive to the repulsive anisotropy of the interaction potential, are used together with the diffraction oscillations of total differential cross section to determine a new rigid rotor potential surface for NH3–He. The potential is constructed by combining large basis set self-consistent-field (SCF) calculations with damped long range dispersion coefficients. The two free parameters of the damping function are determined by fitting the measured data to calculations using the quantal coupled states approximation. The potential is in reasonable agreement with calculations where correlation effects are included and reproduces the measured second virial coefficients.