Quantum mechanical calculations on weakly interacting complexes

Abstract

Symmetry-adapted perturbation theory (SAPT) has been applied to compute the intermolecular potential energy surfaces and the interaction-induced electrical properties of weakly interacting complexes. Asymptotic (large R) expressions have been derived for the contributions to the collision-induced properties up to and including second order in the intermolecular potential. The computed interaction-induced polarizability for the helium diatom has been used in quantum-dynamical calculations of the binary collision-induced Raman spectra.A quantum-statistical expression has been derived for the second virialcoefficient of the dielectric Clausius-Mossotti function. Calculations of the second dielectric virial coefficient of helium gas at various temperatures have been reported. A SAPT potential has been applied in the calculation of bound state levels and the infrared spectrum for the 3He-CO and 4He-CO complexes. Similar calculations have been performed for the infrared spectrum of the Ne-C2H2 and Ne-C2HD complexes. A SAPT potential energy surface for the Ar-CH4 complex has been used in converged close-coupling calculations to generate state-to-state integral cross sections and total differential cross sections for rotational excitation of methane in collisions with argon. SAPT potentials have been applied to compute second virial coefficients (including first-order quantum corrections) for various atom-molecule complexes over a wide range of temperatures. State-to-state elastic and rotationally inelastic differential cross sections for He + C2H2 scattering have been obtained by means of converged close-coupling calculations. From these state-resolved data total differential cross sections and energy loss spectra have been determined. Pressure broadening coefficients and state-to-state rate constants for the rotational (de-)excitation of He-C2H2 have been obtained by means of converged close-coupling and coupled-states calculations. Ab initio SAPT potentials are found to yield observable properties that are in good agreement with the corresponding measured values.