Vacuum-ultraviolet absorption spectrum of the Rb+ ion in a laser-generatedplasma

Discrete features due to 3d photoexcitation in Rb+ have been observed and m easured in the 100-140 eV photon energy range using the dual laser-produced plasma technique. Lines due to 3d(10)4S(2)4p(6)-3d(9)4s(2)4p(6)np (n = 5-8 ) are identified with the aid of configuration-interaction Hartree-Fock cal culations. An upper limit of 0.1 eV for the linewidths of the 3d(9)4S(2)4p( 6)5p and 3d(9)4S(2)4p(6)6p levels was deduced from the data. This value is comparable to Auger widths obtained from electron spectroscopy of near neig hbours atomic Kr and Rb. The Hartree-Fock calculations also predict that th e np electron is largely a spectator in the decay of the 3d(-1)np states. T he overall appearance of the spectrum is accounted for by a relativistic ti me-dependent local density approximation (RTDLDA) calculation. Above the 3d threshold, the relative photoionization cross section is seen to increase monotonically reaching a peak near 200 eV This observation is explained as a delayed onset in the 3d-epsilonf crass section.