ELECTRON CORRELATION EFFECTS ON EXCITATION-ENERGIES OF LOWEST TRIPLET-STATES OF GLYOXAL
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In an attempt to understand the ordering of excited states of glyoxal the 1 A g ground state and low-lying triplet states 3 A u , 3 B u , and 3 B g have been studied with ab initio correlated wavefunctions. A double zeta basis set was used in the configuration interaction calculations, and 6000 Slater determinants were selected for each electronic state. The predicted CI adiabatic excitation energies T e are 21800 cm -1 ( 3 A u ), 25 100 cm -1 ( 3 B u ), and 29 300 cm -1 ( 3 B g ). The effects of d functions and higher (than double) excitations (unlinked clusters) have also been evaluated. For the 3 B u state, both d functions and higher excitations raise the predicted T e value by perhaps as much as 5000 cm -1 . For the 3 B g state, d functions raise the predicted excitation energy but higher excitations have the opposite effect. It is concluded that the excitation energy of the 3 B u state is dramatically increased by correlation effects, while T e for the 3 A u and 3 B g states is markedly decreased by correlation. Copyright 1977 American Institute of Physics.
