Internal dynamics of van der Waals complexes. II. Determination of a potential energy surface for ArHCl

Abstract

The Born–Oppenheimer angular‐radial separation method for calculating ground state properties of atom‐diatomic complexes has been used to determine a potential energy surface for ArHCl. Using a nonlinear least squares procedure, the calculated properties from trial surfaces were fit to molecular beam electric resonance data including both radial and angular expectation values. The inclusion of coriolis coupling terms in the Hamiltonian were found to have a small but discernable effect on the calculated properties. Both the number and type of parameters used to describe the surface affected their correlations dramatically. Fitting the angular properties of the complex required the potential to have an anisotropic to isotropic strength ratio of about 1:2. The isotropic portion of the potential could not be uniquely determined from the bound‐state data alone, but was fixed by predicted differential elastic scattering cross‐sections. In terms of R, the length of the vector connecting the Ar and the center of mass of the HCl, and ϑ, the angle the HCl makes with that vector, the surface has the form: V (R,ϑ) =V₀(R)+V₁(R) P₁(cosϑ) +V₂(R) P₂(cosϑ), with V₀(R) =133 cm⁻¹[0.43 exp{20.[1−(R/3.81 Å)]}−1.43 (3.81 Å/R)⁶], V₁(R) =41.2 cm⁻¹[2.083 exp{10.36[1 −(R/4.259 Å)]}−3.083(4.259 Å/R)⁷], V₂(R) =29.8 cm⁻¹ [1.376 exp{10.36[1.−(R/4.259 Å)]}−2.376 (4.259 Å/R)⁶].