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 [H 3 O] − anion, an intermediate in the anion−molecule reaction of water, H 2 O, 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 H 2 O−H − vibrational stretching mode, based on anharmonic calculations within the vibrational perturbation theory and vibrational configuration interaction. Although the D 2 O•D − species has the lowest energy, our experiments confirm the D 2 O•H − isotope to be a sink of the H/D exchange reaction. Ab initio calculations corroborate that the formation of D 2 O•H − is favored, as the zero-pointenergy difference is larger between D 2 and H 2 than between D