Energy-Shift Theory of Low-Lying Excited Electronic States of Molecules

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Abstract
The present research is directed toward understanding the low‐lying excited electronic states of atoms and molecules. Such excited states play essential roles in atmospheric photochemistry,charge transfer processes, and chemical reactiondynamics. The excitation energies and oscillator strengths between these states and the ground state are the principal concerns of this investigation. A new theory, referred to as the energy‐shift theory, is put forth as a means of directly calculating molecular electronic excitation spectra. Within this theory, four computationally tractable approximations are developed, two of which allow the use of experimental data on higher states to aid the calculations. The method is shown to have some advantages over other direct calculation schemes currently being used in this and other laboratories, the primary advantage being the separation of low‐ and high‐energy excitations which arises naturally in the energy‐shift formalism. The relation of this approach to Green's function theory is discussed.