THE COMBINATION OF R-MATRIX AND COMPLEX COORDINATE METHODS - APPLICATION TO THE DIAMAGNETIC RYDBERG SPECTRA OF BA AND SR

Full details are presented of the new method of Halley et al for the c alculation of near-threshold resonance-dominated spectra. This method combines the R-matrix and complex coordinate techniques and has necess itated an extension of quantum defect theory to calculate an appropria te irregular Coulomb function for complex energy and complex radial di stance. The method is discussed in particular in its application to th e near-threshold photoabsorption spectra of a non-hydrogenic atom in a laboratory strength magnetic field and applied here to the examples o f strontium and barium. Excellent agreement is obtained with experimen tal measurements.