Rotational branching ratios and photoelectron angular distributions in resonance enhanced multiphoton ionization of HBr via the F 1Δ2 Rydberg state

Results of theoretical studies of rotational ion distributions in the X ^2Π_(1/2) ground state of HB^r+ resulting from (2+1) resonance enhanced multiphoton ionization (REMPI) via the S(2) branch of the F ^1Δ_2 Rydberg state are reported. These results show a strongly parity‐favored ion distribution with about 80% population in the (−) component of the Λ doublet of J^+ rotational levels. The 20% population in the other parity component of the Λ doublet can be seen to be due to odd partial wave contributions to the photoelectron matrix elements which arise primarily from non‐atomic‐like behavior of the electronic continuum. This, in turn, is due to angular momentum coupling in the photoelectron orbital brought about by the torques of the nonspherical molecular ion potential. We demonstrate that the effect of alignment on these ion distributions, although not large, is important. Photoelectron angular distributions and alignment of the J levels of the HBr^+ ions are also presented. Rotational branching ratios and photoelectron angular distributions resulting from (2+1’) REMPI of HBr via several S branches of the F ^1Δ_2 state are also shown for near‐threshold photoelectron energies.