The Al -H 2 cation complex: Rotationally resolved infrared spectrum, potential energy surface, and rovibrational calculations

Abstract

The infrared spectrum of the Al +-H 2 complex is recorded in the H-H stretch region (4075-4110 cm -1) by monitoring Al + photofragments. The H-H stretch band is centered at 4095.2 cm -1, a shift of -66.0 cm -1 from the Q 1(O) transition of the free H 2 molecule. Altogether, 47 rovibrational transitions belonging to the parallel K a=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 +-H 2 has a T-shaped equilibrium configuration with the Al + ion attached to a slightly perturbed H 2 molecule, but that large-amplitude intermolecular vibrational motions significantly influence the rotation..