The Cl-35−–H2 and Cl-35−–D2 anion complexes: Infrared spectra and radial intermolecular potentials

Abstract

Rotationally resolved mid-infrared spectra of the Cl-35–H2 and Cl-35–D2 anion complexes are measured in the regions associated with the H2 and D2 stretch vibrations. The Cl-35–H2 spectrum contains a single Σ–Σ transition assigned to the more abundant ortho H2 containing species. The corresponding Cl-35–D2 spectrum consists of two overlapping Σ–Σ transitions whose origins are separated by 0.24 cm−1, and which are due to absorptions by complexes containing para and ortho D2. The spectra are consistent with linear equilibrium structures for Cl−–H2 and Cl−–D2, although zero-point bending vibrational excursions are expected to be substantial. Ground state vibrationally averaged intermolecular separations between Cl− and the diatomic center-of-mass are deduced to be 3.195±0.003 Å (35Cl−–H2) and 3.159±0.002 Å (35Cl−–D2). Vibrational excitation of the diatomic core profoundly affects the intermolecular interaction and leads to contractions of 0.118 Å (35Cl−–H2) and 0.078 Å (35Cl−–D2) in the vibrationally averaged intermolecular separations. Effective one-dimensional radial potential energy curves are developed. Their form near the equilibrium separation is determined by Rydberg–Klein–Rees inversion of the spectroscopic data, and at longer ranges by averaging the dominant long range electrostatic and induction potentials over the angular motion of the atom–diatomic system. On the basis of these potentials the dissociation energies for Cl-35–H2(o), Cl-35–D2(p), and Cl-35–D2(o) are estimated as 488, 499, and 559 cm−1.