Parametrisation of resonance structures in the multichannel quantum defect theory

Abstract

The resonance structures corresponding to autoionising states interacting with many continua are parametrised using the multichannel quantum defect theory. All the involved continua are taken into account in an effective way, and collisional parameters which describe the position and width of the resonances are then introduced. The interactions between open and closed channels are parametrised in an original way in terms of vectors whose relative orientation allows stabilisation effects to be described. The introduction of a unitary transformation which rotates the 'degenerate' closed channels greatly simplifies the analysis. This theory is well adapted to the case of core-excited Rydberg states of barium, as is briefly discussed.