Oscillator-strength trends in the presence of level crossings

Abstract

A configuration-interaction model is used to study line strengths and $\mathrm{gf}$ values for transitions in which level crossing occurs in either the initial or final state. It is shown that the line strength varies continuously for the lowest eigenstate, for example, but not for the eigenstate with a given dominant component. The latter exhibits marked irregularities in the vicinity of a crossover. Some plots for line strengths are presented showing the possible types of irregularities using a model interaction matrix. Computed $\mathrm{gf}$-value trends for $3p$ or $4p{}_{}{}^2{}_{}{}^{}P-(3\mathrm{}{s}^{2}4s,3s3p^2){}_{}{}^2{}_{}{}^{}S$ transitions, as a function of $Z$, illustrate some of these irregularities.