Electron correlation effects in resonant multiphoton ionization of barium

Angular distributions of energy-resolved photoelectrons and branching ratios for formation of the 6s and 5d configurations of ${\mathrm{Ba}}^{+}$ are reported for resonance-enhanced multiphoton ionization of barium. Three excited states of barium were prepared and photoionized: (5d6p${)\mathrm{}}^3$ $P_1^o$, (5d6p${)\mathrm{}}^3$ $D_1^o$, and (6s6p${)\mathrm{}}^1$ $P_1^o$. For the (5d6p${)}^3$ $P_1^o$ and (5d6p${)\mathrm{}}^3$ $D_1^o$ states, photoelectrons corresponding to the fine-structure levels of the 5d ion core were resolved. For the (6s6p${)\mathrm{}}^1$ $P_1^o$ state the photoelectron angular distributions have been measured as functions of the independently variable angle between the polarization vectors of the exciting and ionizing laser radiation pulses. Approximate theoretical expressions based on direct photoionization of the dominant electron configuration of each excited state are generally successful in accounting for the data, but specific discrepancies are noted. Significant intermediate-state interactions are required to account for details of the observations, and some final-state interactions are also implied.