Statistical and dynamical influences on electronic branching in reactions of ground- and excited-state alkaline earth atoms with molecular oxidants

We develop statistical predictions for the branching ratios into the various energetically allowed product electronic states in the reaction of Ca(4s4p³p) + O₂, CO₂, and N₂O as well as Ba(6s^{2 1}S) + N₂O. The statistical branching ratios, based solely on the total volume of translational phase space associated with each electronic channel, can be constrained to be consistent with the conservation of electronic spin and/or electronic adiabaticity. By making use of earlier formal work of Levine, Bernstein, and co-workers, it is further possible to incorporate available information on the internal energy distributions in the various product electronic channels. In the reactions of metastable calcium the experimentally determined branching ratios into electronically excited CaO products are larger than would be predicted by a purely statistical model, whereas the converse seems to be true for the oxidation of Ba(¹S) by N₂O. Also, the experimental branching ratios appear consistent with a dynamical model which allows surface crossings and changes in electronic multiplicity. These oxidation reactions are interpreted in terms of an electron-jump mechanism involving a single charged ion-pair intermediate.