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Abstract:
Orbital correspondence analysis in maximum symmetry of the photoisomerization of naphthvalene to naphthalene, with predominant formation of its lowest triplet, is inconsistent with the assignment of the first excited singlet of naphthvalene to the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) state, 1B1, suggesting instead that it is the totally symmetric open-shell singlet 1A1′. Computations with modified neglect of diatomic overlap and the correlated version of modified neglect of diatomic overlap confirm that the HOMO and LUMO indeed have b2 and a2 symmetry respectively, but that the first-order configuration interaction stabilizes 1A1′ sufficiently to bring it below 1B1. These results illustrate the value of orbital symmetry analysis of photochemical reactions as an aid in the characterization of the relevant excited states and the necessity, in the present instance, of including configuration interaction, even for the purposes of qualitative discussion.
