Precursor state of chemi-ionization reactions and confinement of valence electrons by anisotropic intermolecular forces

Modifications in atomic alignment and in molecular alignment/orientation determine a differentstructure of the adduct, formed by collisions of reagents, which represents the precursor state of manyelementary chemical–physical processes. The following evolution of the system is directly controlled by theconfinement of interacting partners in such a precursor state. However, a deep characterization of thesephenomena is still today not fully available, especially when weak intermolecular forces are operative,although the inquiry is of general relevance for the control of the stereodynamics of processes, occurringunder a variety of conditions both in gas phase and at surface. In this paper recent advances in theknowledge of the selective role of atomic alignment and molecular orientation effects on the stereodynamicsof chemi-ionization reactions will be presented and discussed. These advances represent a basic step alonga path whose final target is the complete and internally consistent rationalization and revaluation of theexperimental findings already obtained, and published, in our and in other laboratories on chemi-ionizationreactions involving as reagent molecules which are of great relevance in several fields. The basic idea is toexport important guidelines provided by a recent detailed study of chemi-ionization of noble gas atomsto more complex reactions involving molecules. The main focus of the present paper is on the quantumconfinement effects of valence electrons within the reaction transition state.