Interaction of vacuum ultraviolet photons with molecules. Formation and dissociation dynamics of molecular superexcited states

A survey is given of recent progress in experimental studies of photoabsorption, photoionization, and photodissociation of molecules in the wavelength range of photons in the vacuum ultraviolet. Corresponding photon energies are 10-50 eV, at which most of the optical oscillator strength of molecules are distributed. Examples of molecules chosen here range from simple diatomic and triatomic molecules to polyatomic molecules such as hydrocarbons, alcohols, ethers, and some Si-containing compounds in the gas phase. Some remarks are presented on molecules in the condensed phase. A particular emphasis in the survey is placed on current understanding of the spectroscopy and dissociation dynamics of molecules in the superexcited states which are produced in the interaction of photons in this wavelength (or energy) range with molecules. A comparative survey is also given of the spectroscopy and dynamics of superexcited states which are produced in electron-molecule collisions. Most of the observed superexcited states are assigned to high Rydberg states which are vibrationally (or/and rotationally), doubly, or inner-core excited, and converge to each of ion states. Non-Rydberg superexcited states are also observed. Some remarks are also presented of superexcited states as reaction intermediates or collision complexes in electron-ion recombination, electron attachment, and Penning ionization processes. (C) 1999 Elsevier Science B.V. All rights reserved.