The Molecular Orbital-Valence Bond Theory of Excited States

Abstract

The original monograph introducing qualitative Valence Bond (VB) and Molecular Orbital Valence Bond (MOVB) theory to the chemical community was entitled “Unified Valence Bond Theory of Electronic Structure”.1,2 In this work, we begin to justify the use of the adjective “unified” by showing how the same MOVB concepts that are applicable to ground state chemistry can be applied to excited state chemistry. In particular, we shall use the MOVB theory and the accessory conceptual tools developed before in order to elucidate the energetic interrelationships of the low lying excited states of a given system and discover ways in which the energy ordering of these states can be altered. After reading the chapter describing the Induced Deexcitation model and this one, it is hoped that the reader will have no difficulty seeing that the energy ordering of different molecular states at fixed geometry and the energy ordering of different ground state geometrical structures are analogous problems which can be handled by the same MOVB concepts.