Approximate Representation of the Diabatic Electronic Wavefunction

The single-configuration approximation is an approximate representation for the diabatic electronic function. Such an approximation is expected to result in 

This integral has been evaluated ab initio and found equal to 300 cm-1 (Felen-bok and Lefebvre-Brion, 1966). (The one-center part of this integral is approximately the nonzero atomic integral sp 1/ r 12]dp).) This calculated value is in fair agreement with the semiexperimental value of 450 cm-1 found by a deperturbation procedure (Jungen, 1966). Note that this electrostatic interaction is responsible not only for perturbations between states of identical symmetry but also for predissociation (Section 7.8.1) and auto-ionization (Section 8.8). 

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