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 thresholds. The spectrum includes the Sr I , , and doubly excited series which converge to the or 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 . At the most significant autoionizing resonance, around , the absolute cross section was measured as . 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