Knowledge Bank

Theoretical electronic transition probabilities for high and low energy transitions of a large number of diatomic molecules have been calculated. Ground state wavefunctions as a superposition of configurations have been used with a frozen core approximation for the excited state. To some extent ground state SCF and correlation effects can be distinguished. Particularly important, for low energy transitions, is non-dynamical (near degeneracy) correlation involving the principal hole-pair of the closed shell ground state and excited orbitals. An effect of this kind which had previously been discovered in the resonance transition of Be $atom1,2$ arising from $(2s)2p$ near degeneracy is found to be present in diatomic molecules (i.e. $Be2,C2$) when population analysis of the LCAO-MO shows the hole MO to be largely 2s and the particle MO largely 2p. Very large R dependent changes in the purely electronic transition probability occur when the degree of principal hole-pair non-dynamical correlation depends on the internuclear distance, This effect occurs in intravalence shell transitions between MO which are degenerate for separated atoms. Examples of R dependent transition probabilities are drawn from our recent calculations on $H2,F2$ and other diatomics.