Quenching of transition arrays through configuration mixing

In the atomic central-field model, the cancellation of some electric-dipole line strengths is a well known effect of configuration mixings. The authors study their global effects on transition arrays. A crucial quantity is the wavenumber mu ₁ of the centre of gravity of two transition arrays when their upper or lower configurations mix. A closed formula is derived for the difference delta E_mix between the values of mu ₁ with and without the mixing effects. Two experimental examples are presented. In the first one, the value of delta E_mix is a sufficient proof that one of the two arrays is almost completely quenched by the other. In the second one, the quenching is only partial, and the degree of quenching is evaluated. In conclusion using the unresolved transition array (UTA) formalism, it is possible to determine ab initio the centre of gravity of a mixed array, without any need for diagonalisation, and to deduce the main effects of configuration mixing.