Diradicals

Abstract

The four states—two diradical states and two zwitterionic states—which arise for a pair of weakly interacting electrons are described in detail for a series of simple systems (twisted ethylene, etc.). Simple rules of thumb are given for the intersystem crossing probability, via spin-orbit coupling, between singlet diradical state and triplet diradical state. Finally it is shown that the knowledge of the relative energies of diradical and zwitterionic singlet states, combined with the chemistry of photochemical reaction intermediates, may lead to a useful classification of photochemical reactions. © 1973, Walter de Gruyter. All rights reserved.