Formation and Dissociation Dynamics of Molecular Superexcited States

This is a survey of recent progress in experimental studies of spectroscopy and dynamics of molecules in the superexcited states. The Platzman’s concept of the superexcited states deduced from the theoretical analysis of the interaction of ionizing radiation with matter has been recently substantiated experimentally. Most of the observed superexcited states are assigned to high Rydberg states which are vibrationally (and/or rotationally), doubly, or inner-core excited, and converge to each ion state. Non-Rydberg superexcited states are also observed. The dissociation dynamics of these states as well as the products are very different from those of the lower states excited below ionization thresholds. The neutral dissociation is unexpectedly more important than ionization. Molecular superexcited states are described as reaction intermediates in some fundamentally important collision processes, e.g., electron-ion or ion-ion recombination, Penning ionization, and electron attachment, and are described also as important species in the primary processes of radiation chemistry, VUV-photochemistry, and plasmas. Comments are presented on molecular superexcited states in the condensed phase. Finally, the future perspectives of the present studies are summarized.