A study of the ArCl2 Van der Waals complex: Ab initio-based potential energy surfaces, the relative stability of conformers, and the “hidden” microwave spectrum

Abstract

Two new ground state potential energy surfaces have been obtained for the ArCl2 Van der Waals complex, one purely ab initio, the other constructed from empirical ArCl potentials modified in terms of ab initio data for the ArCl2 and ArCl moities. The ab initio surface has a well for the linear conformer that is slightly deeper than that for the T-shaped conformer, but inclusion of the zero-point energies reverses the relative binding in the two configurations. The microwave spectrum has been calculated using the new potential surfaces, and a series of lines that can be associated with the linear conformer have been predicted. Possible reasons for their nonobservability under the usual experimental conditions are discussed. A simple modification which employs empirical information on the ArCl potentials used in modelling the ArCl2 potential surface transforms the well for the T-shaped conformer into the global minimum, with a dissociation energy that lies within 0.5% of the experimental value, and microwave transition energies that deviate from experimental values by no more than 1.3%. A final two-parameter scaling allows reproduction of both the experimental D0 value (within experimental uncertainty) and the positions of all observed microwave lines (within 0.02%) for each of the ab initio and empirically based potential surfaces.