Excited state-selected transition metal cations from one-color UV multiphoton ionization

Abstract

We have used one-color, resonance enhanced multiphoton ionization in the near-UV to create selectively the first excited terms of the transition metal ions Fe+, Ti+, and V+ in the gas phase. The term and level distributions of the resulting photoions are measured using time-of-flight photoelectron spectroscopy. We generally find better electron configuration and term selectivity for two-photon ionization via 4p resonant Rydberg levels than was found in previous work on three-photon ionization of 5s Rydberg levels. In certain Fe cases, a single ion total angular momentum level dominates the photoelectron spectrum. The simple picture of the 4p Rydberg levels as consisting of an ion core of well defined Lc–Sc and Jc weakly coupled to a Rydberg electron is remarkably useful. Deviations from this simple picture are discussed in terms of configuration interaction of resonant states and autoionizing structure in the continuum. The results will find application in studies of state-selected metal ion chemistry.