Photoelectron Imaging Spectroscopy for (2+1) Resonance-Enhanced Multiphoton Ionization of Atomic Bromine

摘要

Two-photon resonant third photon ionization of atomic bromine (4p5 2P3/2 and 2P1/2) has been studied using a photoelectron imaging spectroscopy in the wavelength region 250 - 278 nm. The technique has yielded simultaneously both relative branching ratios to the three levels of Br+ ( 3P2, 3P0,1 and 1D2) with 4p4 configuration and the angular distributions of outgoing photoelectrons. The product branching ratios reveal a strong propensity to populate particular levels in many cases. Several pathways have been documented for selective formation of Br+ ( 3P2) and Br+ ( 3P0,1) ions. In general, the final ion level distributions are dominated by the preservation of the ion core configuration of a resonant excited state. Some deviations from this simple picture are discussed in terms of the configuration interaction of resonant states and the autoionization in the continuum. The photoelectron angular distributions are qualitatively similar for all transitions, with a positive A2 anisotropy coefficient of 1.0 - 2.0 and negligible A4 in most cases, which suggests that the angular distribution is mainly determined by the single-photon ionization process of a resonant excited state induced from the third photon absorption.