van der Waals coefficients through C8 for atom–linear molecule interactions. I. CO2–noble gas systems

Abstract

Exact formulas for all the terms in the van der Waals C₇ and C₈ coeffcients for the interaction of an S‐state atom with a Σ‐state linear molecule are derived. The angle dependence is presented in convenient Legendre polynominal expansion form. Procedures for the calculation or estimation of the coefficients are proposed, discussed, and applied to CO₂–noble gas atom interactions. Simple formulas are found to give good bounds for the angle‐dependent part of C₆. Although the uncertainties in the estimates of the higher coefficients are large, using them instead of C₆ alone improves the long range potential considerably.