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 different structure of the adduct, formed by collisions of reagents, which represents the precursor state of many elementary chemical–physical processes. The following evolution of the system is directly controlled by the confinement of interacting partners in such a precursor state. However, a deep characterization of these phenomena 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, occurring under a variety of conditions both in gas phase and at surface. In this paper recent advances in the knowledge of the selective role of atomic alignment and molecular orientation effects on the stereodynamics of chemi-ionization reactions will be presented and discussed. These advances represent a basic step along a path whose final target is the complete and internally consistent rationalization and revaluation of the experimental findings already obtained, and published, in our and in other laboratories on chemi-ionization reactions involving as reagent molecules which are of great relevance in several fields. The basic idea is to export important guidelines provided by a recent detailed study of chemi-ionization of noble gas atoms to more complex reactions involving molecules. The main focus of the present paper is on the quantum confinement effects of valence electrons within the reaction transition state. Graphic abstract