Short communication

The relative cross section for Ba⁺⁺ and Ba⁺ ions from Ba atoms with helium and neon resonance photons

The dependence of satellite structure in the atomic UV photoelectron spectra of Zn, Cd and Hg on photon wavelength has been examined by using both Hel 584 Å and Hell 304 Å sources. Apart from work on He and some qualitative observations on other atoms, there have previously been no studies on the wavelength dependence of correlation satellite intensities. The main lines in the spectra correspond to (n − 1)d¹⁰ns²S_{$\text{1}\text{2}$} and (n − 1)d⁹ns²; ²D_{$\text{5}\text{2}$} and ²D_3/2 final states, and the satellites are the (n − 1)d¹⁰np; ²P_{$\text{1}\text{2}$}, ²P_{$\text{3}\text{2}$} lines. The relative intensities of the satellites with respect to that of the ²S_{$\text{1}\text{2}$} line are found to be essentially independent of photon energy for all three Group IIB atoms, strongly suggesting that their intensity is due in each case to the initial state configuration interaction (ISCI) mechanism. This result is consistent with the near degeneracy of the ns and np shell energies, which facilitates strong admixture of the configuration (n − 1)d¹⁰np²; ¹S into the ground state of these atoms.

Thermal energy (40—400 meV) ionizing collisions between He(2³S, 2¹S) metastables and Ba, Y, and Ce atoms have been studied in a crossed-beam experiment, in order to investigate the role of two-electron ejection as compared to that of single ionization. The fraction of double ionization is found to be small in all cases (<3%). The results are qualitatively explained on the basis of the electron exchange model for Penning solution.

The 21.22-eV photoelectron spectrum has been measured from a barium beam. Aside from the ground state of Ba⁺, the first six excited states of this ion have been identified. An unusually high relative cross section for the production of Ba²⁺ and excited Ba⁺ compared to Ba⁺ in its ground state is found. An explanation is proposed involving the autoionizing (5p)⁵(6s)²²P_1/2 state of Ba⁺. From this the binding energy of the 5P_1/2 electrons of Ba is found to be 21.1 eV.