Two-photon spectroscopy of dipole-forbidden transitions. II. Calculation of two-photon cross sections by the CNDO-CI method

Abstract

The applicability of a CNDO/S scheme including double excited configurations for the calcn. of excitation energies of larger unsatd. mols. was studied. The same scheme is very useful for the prediction of 2-photon transition probabilities. If the proper expansion is used, the results converge quite well with increasing no. of intermediate states. The inclusion of double excited configurations is not only necessary to obtain better energies for dipole-forbidden transitions to covalent excited states but also to obtain the correct order of magnitude for 2-photon cross sections.