Common window resonance features in K and heavier alkaline atoms Rb and Cs

A previous study of subvalence s-shell photoionization of potassium [Koide et al.: J. Phys. Soc. Jpn. 71 (2002) 1676] has been extended to the cases of heavier alkaline atoms Rb and Cs. We have measured the photoion time-of-flight spectra using monochromatized synchrotron radiation. Dual windows resonance structure previously observed in K was also found in Rb and Cs, suggesting that those structure are general features in alkaline atoms. We have observed also the Rydberg series of resonances that appear in dual windows. Our data analysis shows that the resonance widths are broad when compared with its rare gas neighbors. Based on multiconfiguration Dirac-Fock calculations, the Rydberg series of resonances were assigned to the 4s14p65s5p excitations embedded in the 4p55s continua for Rb and to the 5s15p66s6p excitations embedded in the 5p56s continua for Cs. (author)