Anisotropic Intermolecular Force Effects in Spectra of H2– and D2–Rare-Gas Complexes

Abstract

Spectra of H2–Ar, H2–Kr, and H2–Xe Van der Waals complexes, accompanying the Q1(0), S1(0), Q1(1), and S1(1) transitions of the pressure-induced fundamental absorption band of hydrogen, have been studied in a path length of 165 m at temperatures in the range 85–158°K. At the low total gas densities used, 1–2 amagat, the lifetimes of the complexes were sufficiently long to show a great deal of new detail in the spectra. The R and P branches (δl = ± 1, where l is the angular momentum of the complex) accompanying the overlap-induced Q1(0) transitions, could be analyzed on a nonrigid rotation model to give Lennard-Jones ε and Σ parameters for the molecular pairs. The spectra accompanying the quadrupole-induced S1(0), Q1(1), and S1(1) transitions show T and N (δl = ± 3) as well as P and R branches, and many of the lines are split by the anisotropy of the intermolecular forces. The splitting is qualitatively in agreement with a model with loose coupling between J, the angular momentum of the H2 molecule, and 1. Well-resolved spectra of D2–Ar, D2–Kr, and D2–Xe complexes accompanying the S1(0) transition of deuterium were also obtained; these show more bound states than the H2–rare-gas spectra and anisotropic interaction effects are evident. The H2–N2 complex shows a spectrum with a diffuse structure not previously observed.