On the photoionisation of Ba atoms between 54 and 60 nm

Using monochromatised synchrotron radiation in conjunction with a crossed-beam apparatus and a quadrupole mass spectrometer the authors have measured the relative cross sections q + for single and q 2+ for double photoionisation of Ba atoms as well as the ratio R=q 2+ /q + in the wavelength range 60-54 nm with 0.09 nm bandwidth. Compared with other experimental data, measured with a bandwidth of about 0.2 nm, their data show much more structure. In the interesting region around 58 nm, the Ba 2+ yield has been studied with a resolution of 0.015 nm; the comparison with photoabsorption data of Ederer et al. (1975) shows good agreement in the peak structure, and at the same time calls for additional experimental studies of the problem with the highest possible resolution.