A comprehensive study of the differential cross sections for water–rare gas collisions: experimental and theoretical perspectives

Abstract

Experimental measurements and theoretical quantum calculations of the inelastic differential cross sections for the collisions of H₂O with Ne, Ar and Xe atoms are respectively compared at the 364, 390 and 351 cm⁻¹ collision energies. The four rotational excitation transitions 0₀₀ → 1₁₁, 1₀₁ → 2₁₂, 1₀₁ → 1₁₀ and 1₀₁ → 2₂₁ are studied for the three systems. The experimental setup consists of a crossed molecular beam machine with velocity map imaging complemented with state-selective laser ionization detection. The theoretical approach is based on close-coupling calculations of rare gas scattering by rigid H₂O, using two recently developed potential energy surfaces for Ne + H₂O and Ar + H₂O systems as well as a new potential energy surface developed in this work for the Xe + H₂O system. Measured and calculated differential cross sections are in good agreement. The integral cross section is increasing in proportion to the mass of the rare gas atom. This can be attributed to the rise of the rare gas polarizability along with the rise of the dissociation energy and reduced mass of the Rg–H₂O complex. The fast oscillations observed in the calculated differential cross sections attest that the collision dynamics is mainly driven by the repulsive part of the interaction potential, as could be expected since the collision energies are much larger than the dissociation energies.