Zero-Point-Energy Driven Isotopic Exchange of the [H3O]- anion Probed by Mid-Infrared Action Spectroscopy

Abstract

We present the first observation of vibrational transitions in the [H₃O]⁻ anion, an intermediate in the anion-molecule reaction of water, H₂O, and hydride, H⁻, using a laser-induced isotopic H/D exchange reaction action spectroscopy scheme applied to anions. The observed bands are assigned as the fundamental and first overtone of the H₂O-H⁻ vibrational stretching mode, based on anharmonic calculations within the vibrational perturbation theory and vibrational configuration interaction. Although the D₂O·D⁻ species has the lowest energy, our experiments confirm the D₂O·H⁻ isotope to be a sink of the H/D exchange reaction. Ab initio calculations corroborate that the formation of D₂O·H⁻ is favored, as the zero-point-energy difference is larger between D₂ and H₂ than between D₂O·H⁻ and D₂O·D⁻.