THEORY OF X-RAY-EMISSION OF CONJUGATED MOLECULES

A theory of nonresonant x-ray emission spectra of conjugated molecules is presented. The role of relaxation effects on the spectral shape of x-ray emission is advanced and examined in detail for the transpolyen es. In some contrast to unconjugated systems, the relaxation of valenc e charge around the core hole is shown to influence the distribution o f x-ray intensities significantly. Site and size dependences of the sp ectral shape of x-ray emission are predicted; the site dependence as b eing alternant among the pi levels. Comparative calculations of x-ray emission spectra at the ab initio Hartree-Fock and the semiempirical l evels show that the relaxation qualitatively changes the spectral dist ribution and shifts intensity from the sigma to the pi parts of the sp ectra, creating excitonlike features in the latter. The exciton charac ter is site and size dependent; for longer polyenes it is stronger for mid-atoms than for end-atoms, and is found stronger at the top than a t the bottom of the pi band. Complication/simplification trends of the spectra along the oligomer sequence are predicted for both the relaxe d and frozen orbital models. (C) 1996 American Institute of Physics.