The Al –H2 cation complex: Rotationally resolved infrared spectrum, potential energy surface, and rovibrational calculations

Abstract

The infrared spectrum of the Al+–H2 complex is recorded in the H–H stretch region (4075–4110cm−1) by monitoring Al+ photofragments. The H–H stretch band is centered at 4095.2cm−1, a shift of −66.0cm−1 from the Q1(0) transition of the free H2 molecule. Altogether, 47 rovibrational transitions belonging to the parallel Ka=0-0 and 1-1 subbands were identified and fitted using a Watson A-reduced Hamiltonian, yielding effective spectroscopic constants. The results suggest that Al+–H2 has a T-shaped equilibrium configuration with the Al+ ion attached to a slightly perturbed H2 molecule, but that large-amplitude intermolecular vibrational motions significantly influence the rotational constants der..