Molecular dynamic photoelectron spectroscopy using resonant multiphoton ionization for photophysics and photochemistry

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Abstract
Photoelectron kinetic-energy spectra of resonant multiphoton ionization of gaseous molecules are regarded as ‘photoelectron spectra of the resonant intermediate excited states’. Therefore, such a technique using resonant multiphoton ionization or stepwise ionization with a tunable pulse U.V./visible laser makes it possible to observe excited-state photoelectron spectra for various molecules and molecular complexes in the gas phase. Molecular nonradiative electronic states for which direct observation is difficult by fluorescence spectroscopy can be studied by this technique. It is possible to study not only static but also dynamic aspects of various molecular excited states from the point of view of photoelectron spectroscopy. In this sense, such photoelectron spectroscopy may be called ‘dynamic photoelectron spectroscopy’. This is in striking contrast to VUV photoelectron spectroscopy which is mostly concerned with static aspects of ground-state molecules, although information on the dynamics of ionization processes can be obtained. Molecular dynamic photoelectron spectroscopy will be fruitful especially for studying dynamic aspects of molecular excited states from the photophysical and photochemical points of view. The present article is concerned mainly with dynamic photoelectron spectroscopy and its application to molecular processes such as photodissociation, autoionization, and intramolecular relaxation.