Absolute photoabsorption cross sections of strontium have been measured in the energy range extending from the 5p(3/2) threshold up to above the 6s threshold. The synchrotron radiation source of the Synchrotron Radiation Research Center at Hsin-Chu was used as the background continuum. Strontium vapour was confined in a heatpipe oven. The absolute column density was determined by simultaneously measuring the temperature distribution profiles and the total pressure in the heatpipe. Absolute cross sections were determined using the Beer-Lambert law. The observed spectrum was analysed using a combination of a recent extension of the jj-coupled eigenchannel R-matrix adapted to handle highly correlated levels and the phase-shifted multichannel quantum defect theory. The main features of the observed spectrum, dominated by the presence of many window-type resonances, are well reproduced and the structures are identified. The observed absorption windows result from the fact that only continua are directly excited from the ground state.
JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS