Photoionization of Excited Molecular States using Multiphoton Excitation Techniques

Abstract

Resonantly enhanced multiphoton ionization (REMPI) affords the opportunity to select a specific ionization pathway in order to produce a particular ionic state for further study or to investigate detailed aspects of excited state photoionization dynamics. The production of electronic or vibrational state-selected ions using REMPI can be achieved by first preparing an intermediate Rydberg state that has a potential energy curve similar to that of the final desired ionic state, and then ionizing the Rydberg state with a single additional photon. Under these circumstances, the Franck-Condon factors governing the final ionization step strongly favor the preservation of the Rydberg state core. Here we demonstrate the final electronic and vibrational state selectivity of REMPI by recording photoelectron spectra following single photon ionization of the 2pπu C 1Πu Rydberg state of H2 (Figure 1) and the (1Πu)3(3σg)2 3sσg o3 1Πu Rydberg state of N2 (Figure 2). Both excited states were prepared by resonant three photon transitions from the ground electronic state. In the case of H2, the C 1Πu Rydberg state converges to the ground electronic state of the ion, and photoionization produces vibrational state-selected ions in the ground electronic state. In the case of N2, the o3 1Πu Rydberg state converges to the first excited state of the ion, and photoionization produces vibrational state-selected ions in an excited electronic state.