Selectively breaking either bond in the bimolecular reaction of HOD with hydrogen atoms

Abstract

We have determined the branching ratio for the reaction of hydrogen atoms and HOD with either the O–H bond excited or the O–D bond excited. In both cases, the initially excited bond reacts preferentially. Excitation of the third O–H stretching overtone, 4νOH, favors breaking the O–H bond by a factor of ∼200, and excitation of the fourth O–D stretching overtone, 5νOD, favors breaking the O–D bond by a factor of ∼220. Thus vibrational excitation can control the H+HOD reaction to produce either product almost exclusively. A simple model using the calculated wave function for each state and the measured reaction cross section for a particular vibrational excitation predicts the high selectivity observed for the two reactions.

Vibrational State Control of Bimolecular Reactions: Discovering and Directing the Chemistry

“…Reactions with both Cl and O atoms behave the same way. 5,6 Driving the reaction in one direction with vibrational excitation does not require that all the energy come from vibration. Bronikowski et al 11 excited the fundamental O-H or O-D stretching vibrations and used translationally energetic H atoms to provide the remainder of the energy.…”

The Dynamics of the H+H2O Reaction

“…It was observed that the reaction to produce OD occurs at least two orders of magnitude more frequently that the reaction to produce OH. Conversely for the reaction given by Equation (6), [86] a 220-fold excess of OH over OD is produced. Thus control of the H HOD reaction in order to produce either product, almost exclusively, can be achieved.…”

A full-dimensional quantum dynamics study of the mode specificity in the H + HOD abstraction reaction

“…Due to its significance in better understanding the polyatomic reaction dynamics, the mode specificity of chemical reactions has been extensively studied both experimentally [1][2][3][4][5][6][7][8][9][10][11][12] and theoretically. The H + H 2 O → H 2 + OH and its analogies are considered as the simplest atom-triatomic reactions, but they offer much richer complexity than atom-diatom reactions.…”