Dynamics of the reactions of Zn(4s4p 3P1) with H2, HD, and D2: Rotational and vibrational quantum-state distributions of ZnH (ZnD) products

Abstract

The complete initial vibrational and rotational quantum state distributions of ZnH(ZnD) products in the reactions of Zn(4s4p 3P1) with H2, HD, and D2 have been determined using a laser ‘‘pump-and-probe’’ technique. The most striking result is that the quantum-state distributions of ZnH (or ZnD) products are essentially unchanged when the mass of the leaving atom is doubled, from H to D. It is suggested that this indicates that simple impulsive bond breaking cannot play a large role in the reaction of Zn(3P1) with H2, and that potential surface anisotropy in the decomposition of bent H–Zn–H insertion intermediates could be responsible for the rotational energy distributions of the products. Similar isotopic results for reactions of Cd(5s5p 3P1), Hg(6s6p 3P1), and O(1D2) with H2, HD, and D2 are noted, and the general implications of the lack of an isotope effect are discussed in detail. The branching ratio of ZnD vs ZnH formation in the reaction of Zn(3P1) with HD was determined to be 1.1±0.2 and it was pointed out that several ‘‘insertion’’ reactions have now been shown to have branching ratios for reaction with HD which are very near 1.0, inconsistent with earlier qualitative arguments that such processes should lead to high branching ratios.