EXAMINATION OF CHARGE-DENSITY WAVES IN VERTICAL EXCITED-STATES OF A LINEAR POLYENE

Applying Moffitt's theorem, we examine if a vertical excited state of a linear polyene can present unfavorable charge density waves (CDWs). It is found that the CDW structure is forbidden in a given electronic MO configuration, if (at least) two MOs with pairing properties are oc cupied by 3 or 4 electrons, and allowed if all the couples of paired M Os involve 0 or 1 or 2 electrons. This is general and applicable to an y long linear polyene, such as polyacetylene. A numerical application is given for the singlet (vertical) excited states of hexatriene. Unfa vorable CDW structures, which, as shown are the result of a purely coo perative effect of the whole electronic assembly, can be created by ve rtical excitation even in the case of a strongly ionic excited state.