Knowledge Bank

The $v3$ infrared band of $SF6$ has been found to have different red shifts, relative to the free molecule frequency, depending on whether the chromophore is situated inside an Ar cluster, at the surface of an Ar cluster, or in an Ar $matrix.1-3$ The present paper describes our work on a model for explaining these shifts in terms of the dependence of the $Ar-SF6$ interaction potential on the vibrational stretching of the $SF6$. The main contribution to this shift is found to arise from the vibrational dependence of the electrostatic field due to the oscillating dipole moment associated with the $v3$ mode of $SF6$. The structures of $SF6-Arn$ clusters and of matrices containing $SF6$ are investigated using the realistic, $empiricaln$ rigid-body $Ar-SF6$ pair potential of Pack $etal.4$ The shifts of the $SF6$ vibrational levels are then predicted by treating the influence of the surrounding atoms using this perturbation theory.