The combination of R-matrix and complex coordinate methods: application to the diamagnetic Rydberg spectra of Ba and Sr

Abstract

Full details are presented of the new method of Halley et al. (1992) for the calculation of near-threshold resonance-dominated spectra. This method combines the R-matrix and complex coordinate techniques and has necessitated an extension of quantum defect theory to calculate an appropriate irregular Coulomb function for complex energy and complex radial distance. The method is discussed in particular in its application to the near-threshold photoabsorption spectra of a non-hydrogenic atom in a laboratory strength magnetic field and applied here to the examples of strontium and barium. Excellent agreement is obtained with experimental measurements.