The Mechanism of Processes Initiated by Excited Atoms I. The Quenching of Excited Sodium

Abstract

The potential‐energy surfaces relevant to a number of simple processes involving excited (²P) sodium have been constructed, and the mechanism of the reactions discussed in terms of them and of the theory of absolute reaction rates. It is shown that quenching by atoms is normally a very inefficient process, the effect of additional atoms in a quencher being to stabilize a quenched complex, commonly a polar compound, which finally decomposes to give the deactivated atom and a vibrationally excited product. The activated state may be either at the top of a rotational‐energy barrier or at a crossing point to a polar surface, and the theory is shown to be consistent with the experimental values of the quenching cross sections. In the cases examined the quenching is of a physical nature, the energy passing chiefly into vibrational energy, with a certain amount going into translational and rotational degrees of freedom. Saturated hydrocarbons appear to quench like hydrogen except that there is probably a small energy of activation, but the unsaturated ones quench by means of an interaction between the sodium atom and the unsaturated group, and the efficiency is considerably higher.