SPECTROSCOPIC CONSTANTS OF $O_{2}{^{-}}$ ELECTRONIC STATES IN VACUO AND IN IONIC SOLIDS
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Date
1990
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Ohio State University
Abstract
MCSCF and MCSCF/CI computations have been carried out for the ground and several excited states of $O_{2}$-both in vacuo and in simulated ionic lattices. The potential energy curves are fitted to modified Morse functions. The $a^{4}\Sigma_{a}{^{-}}$ state is unique in representing a stable anionic excited state in the gas phase, while the $A^{2}\Pi_{u}$ state is metastable. From stability plots the $a^{4}\Sigma_{u}{^{-}}$ state is unstable with respect to electron autodetachment at bond lengths where it lies above the ground state of $O_{2}$. The effect of an ionic host lattice on the spectroscopic parameters is simulated by an array of point charges in which the anion is oriented $<100>, <110>, or <111>$. All electronic states examined are electronically stable in these lattices. However the spectroscopic constants, particularly of the more highly excited states, differ markedly from those in the gas phase. The $^{4}\Sigma_{u}{^{-}}$ states exhibit an avoided crossing with no analog in the gas phase. A pronounced crystal-field splitting is found for all $\Pi$ states in the $<110>$ lattice. The computed spectroscopic properties of the $A \leftrightarrow X$ transition are compared with experimentally known absorption and luminescence spectra that have been attributed to this system in alkali halide hosts
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Author Institution: Department of Chemistry, Vanderbilt University