Photoionization of Excited Molecular States

Abstract

Rapid advances in laser and detector technologies are making it possible to investigate molecular photophysics and photochemistry in powerful new ways. For example, resonantly enhanced multiphoton ionization (REMPI) measurements, in which the total (or the mass selected) ion current is monitored as a function of laser wavelength, have yielded extensive and often novel information on the spectroscopy of the resonant intermediate states [1]. With the addition of photoelectron spectrometry (PES) to analyze the kinetic energy of the ejected electrons, it is possible to determine the branching ratios into different electronic, vibrational, and rotational levels of the product ion and to focus directly on both the dynamics of the multi photon ionization process and the photoionization of excited state species [2–9]. In the present paper, we report several REMPI/PES studies of H2 and N2. The results reflect both the spectroscopy and the dynamics of pnotoiomzation of excited molecular states and are discussed in terms of the selection rules for photoionization and the relative probabilities of photoionization from Rydberg and valence states. In some cases, in accordance with the Franck-Condon principle, the results demonstrate that resonant multi photon ionization through Rydberg states may be a powerful technique for the production of electronic, vibrational, and rotational state selected ions.