R-Matrix Calculation of Multichannel Quantum Defect Parameters in Heavy Alkaline Earth Atoms

Abstract

The alkaline earth atoms have been the subject of numerous recent laser experimental investigations. The major motive for the interest in these spectra is the ability to study the strong interchannel interactions which cause irregularities in bound Rydberg series and autoionizing structures. The multichannel quantum defect theory (MQDT)1–4 has enjoyed remarkable success in interpreting the data obtained in the heavy alkaline earths Ca, Sr and Ba5,6. However most of the previous analyses use empirical MQDT parameters which are adjusted to agree with a particular set of measurements. The complexity of heavy elements is such that empirical MQDT treatments come against difficulties related to the energy dependence of the parameters, to the occurrence of isolated perturbers and to the presence of a too large number of interacting channels. This has made desirable to develop techniques to calculate the energy-dependent short-range MQDT parameters.