Abstract. We have measured the double-to-single photoionization ratio of beryllium (1s²2s²) between 32 and 80 eV and compare our data with the electron-impact ionization cross section of Be⁺. In this energy region only simultaneous but not sequential emission of both 2s electrons can take place. We also compare our data with the double-to-single photoionization ratios of He, H₂ and Li and find surprisingly good agreement of the photon-energy dependence if the ratio is scaled appropriately. The double-to-single photoionization ratio is lower for Be than for He due to a weaker electron-electron interaction between the valence electrons.

Print publication: Issue 22 (28 November 2001)
Received 14 August 2001, in final form 27 September 2001
Published 9 November 2001