Empirical potentials for rovibrational energy transfer of hydrogen fluoride in collisions with argon

Rovibrational energy transfer of hydrogen fluoride in collisions with argon was investigated by using the coupled-states approximation to the quantum scattering problem. Empirically determined 3-D ab initio potential energy s urfaces (PES) for the interaction between hydrogen fluoride and argon are p resented. Second-order Moller-Plesset perturbation theory (MP2) was used to provide an initial approximate PES for the complex. The MP2 PES was subseq uently modified to compensate for the underestimated dispersion interaction and adjusted until the desired agreement between calculated and observed s pectroscopic quantities was achieved. Calculated rotational cross sections are in good agreement with experimental results as well as those obtained w ith a highly accurate vibrationally averaged empirical PES [J. M. Hutson, J . Chem. Phys. 96, 6752 (1992)]. The rate constants for the collision induce d relaxation of the first vibrational state of hydrogen fluoride are presen ted as functions of temperature. The rate constants show structure at low t emperature corresponding to cross-section resonances. The calculated rate c onstants are in good agreement with available high temperature experimental results. The calculations provide lower temperature rate constants and a w ealth of detailed state-to-state information that are not available from ex periment. (C) 2001 American Institute of Physics.