Measurements of absolute cross sections for the photoionisation of Ba+ions

Abstract

An apparatus is described in which merged beams of ground-state Ba+ ions and energy-resolved radiation from the Daresbury Synchrotron Radiation Source were used to obtain absolute cross sections for the photoionisation of Ba+ in the wavelength range 420-775 AA (29.5-16.0 eV). Approximately 75 peaks were resolved, the largest of which corresponded to cross sections greater than 10-15 cm2; this indicated very large contributions from inner-shell excitation-autoionisation. Systematic errors were estimated to be less than +or-15% and the energy resolution ranged between 20 and 4 meV. The energies of some of the peaks can be correlated closely with series limits of inner-shell transitions of neutral barium measured by Connerade et al. (1979) and with energies of autoionising states of Ba+ calculated by Hansen (1974-5) and by Griffin et al. (1984) in Hartree-Fock approximations. The energies of some transitions also correspond quite closely with absorption lines observed by Roig (1976) by flash pyrolysis of barium vapour.