The Mechanism of Reactions Involving Excited Electronic States The Gaseous Reactions of the Alkali Metals and Halogens

In many of the reactions of the alkali metals with the halogens the reacting system changes from a homopolar to a polar state, or vice versa. The possibility of a restriction on this change is considered, and it is concluded that there will be a serious restriction only for some of the atomic reactions $$\mathrm{M}+\mathrm{X}\to \mathrm{MX},$$ which are of little importance. The crossing points between the polar and homopolar states for the reactions $${\mathrm{M}}_2+\mathrm{X}\to \mathrm{MX}+\mathrm{M}$$ $$\mathrm{M}+{\mathrm{X}}_2\to \mathrm{MX}+\mathrm{X}$$ are drawn in so close that the interaction is large enough to insure transition. Due to the threefold degeneracy of the initial state of b (which arises because X is in a P state) this reaction has the possibility of leading directly to the excitation of the M atom which is formed. The nature of the potential surfaces for this process are considered. The process first suggested by Polanyi, the excitation of M atoms by vibrationally excited MX molecules, is discussed. This process is possible because of a crossing of the two lowest polar states for the M₂X system. These two surfaces cross for a certain isosceles triangular configuration. Reacting systems thus easily go from the lowest to the second state in this region.