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

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.