Adiabatic Correlation Rules for Reactions Involving Polyatomic Intermediate Complexes and their Application to the Formation of OH(2Σ+) in the H2–O2 Flame

Abstract

Adiabatic orbital and spin correlation rules applicable to a detailed study of elementary chemical reactions involving nonlinear polyatomic intermediate complexes have been formulated and are presented together with some pertinent correlation tables. These correlation rules and tables permit the determination of the adiabatically allowed term manifold of reaction products from the states of the separated reactants without reference to their detailed electronic configurations. The formulation presented here utilizes group theoretical arguments relating to the symmetry properties of the reactants, the intermediate reaction complex, and the products and is based principally upon the results obtained previously by Mulliken for the resolution of species into those of point groups of lower symmetry. The effects of the change of the (geometrical) configuration of the intermediate reaction complex during reaction and of the electronic-vibrational coupling on these correlations have been considered in detail. It is concluded that strict orbital electronic correlation rules are operative only for reactions where neither the reactants nor the products are polyatomic. For reactions involving polyatomic reactants and/or products, the vibrational-electronic coupling weakens the simple orbital electronic correlations so that detailed vibronic correlations will be necessary. The spin correlation rules, however, are not affected by these interactions and are identical with those given by Wigner and Witmer for atomic and diatomic systems. These correlation rules are then applied to a study of the reactions H+O2→[HO2]→OH*+OO+H2→[OH2]→OH*+H which may be of importance in the production of electronically excited OH[OH(2Σ+)] in the hydrogen-oxygen flame. The mechanism of these reactions is investigated with special reference to the predissociating OH(2Σ−) state discussed recently by Gaydon and Wolfhard. It is suggested that the interaction of and the consequent radiationless transition between HO2 intermediate reaction complexes is primarily responsible for the formation of OH(2Σ+) in its observed vibrational nonequilibrium distribution with the specific enhancement of the levels v′=2 and 3. The adiabatic correlations for the special case of association (and dissociation) reactions involving linear polyatomic intermediate complexes and products are considered briefly in the Appendix. It is concluded that vibronic correlations are required for the determination of the product term manifold for these reactions.