Theoretical Transition Probabilities

The contribution to the intensity of atomic and molecular electronic transitions beyond the Hartree—Fock, or independent‐particle model, is examined by means of ``many‐electron theory'' (MET). The contribution is of first order in the wavefunctions of the combining states.MET analysis of the off‐diagonal matrix element for the transition probability in the frozen‐core approximation yields physically interesting expressions which are applied to atomic and molecular examples. Considerable improvement in calculated atomic (e.g., Be resonance transition) and molecular (e.g., π—π* transitions) intensities are obtained when analysis shows that ground‐state ``hole pairs'' are strongly scattered into the orbital sea of the excited state.The uses of energies and operators in the calculation of electronic intensities is also examined. The relation between the expectation values of operators ∇ and r which replaces the widely used off‐diagonal hypervirial theorem in the absence of exact wavefunctions is given.