THE THEORY OF PHOTOACTIVAT ION AND THE PROPERTIES OF PHOTOACTIVATED MOLECULES

In discussing the problem of photoactivation it is necessary to bear in mind the fact that he re-active state of a molecule produced by the action of light may be the same as that produced by thermal activation or it may be quite different. Thus the photochemical nd thermal reactions be-tween hydrogen and bromine to form hydrogen bromide apparently involve the same mechanism, whereas the corresponding reactions between hy-drogen and chlorine proceed by different mechan-isms. In general it may be said that photoacti-vation is less efficient han thermal activation in the sense that the amount of light energy ab-sorbed in producing the reactive states is usually considerably larger than the heat of activation as ~