Absolute photoabsorption cross sections of Sr I from the 5s ionization threshold to the 5p threshold

We have measured the absolute photoabsorption cross sections of Sr I from its 5s ionization threshold up to the 5p_1/2,3/2 thresholds. The spectrum includes the Sr I 4dnp, 4dnf, 5pns and 5pnd doubly excited series which converge to the 4d_3/2,5/2 or 5p_1/2,3/2 series limits. Synchrotron radiation, from the 1 m Seya-Namioka beam line of the Synchrotron Radiation Research Center at Hsin-Chu, Taiwan, was used as the background continuum. The absolute column density was determined by measuring simultaneously the temperature distribution profiles and the total pressure in a heatpipe. Absolute cross sections were obtained using the Beer-Lambert law. The measured absolute cross section for the 5s ionization threshold was 7.2 Mb ± 0.9 Mb. At the most significant autoionizing resonance, 4d6p ¹P around 196 nm, the absolute cross section was measured as 51.0 Mb ± 6.6 Mb. The absolute cross sections presented here are larger than those based on saturated vapour-pressure data, and less than those based on the f-value measurements. All the absolute cross sections in this work are compared with both recent experiments and theoretical calculations.