Alignment and Chirality in Gaseus Flows

Advances in experimental vacuum technology allow the generation of molecular beams containing oriented molecules. We will focus our review on the so-called collisional alignment, a molecular polarization phenomenon occurring in supersonic expansions of gaseous mixtures. The key feature is the velocity dependence of the alignment degree, which allows the use of mechanical devices to select the molecules of the beam having either a random or a preferential spatial distribution of their rotational angular momentum with respect to the molecular beam axis. The physical mechanisms underlying the collisional alignment will be outlined and some relevant gas-phase experiments demonstrating its occurrence will be illustrated permitting the applications of these tools to the study of elementary processes occurring both in homogeneous and heterogeneous phases. Investigation of the stereodynamics of elementary processes provides the background for perspective demonstration of manifestation of chiral effects in molecular collisions. This latter topic, in view of its fundamental relevance and also of interest in a protobiological context, is elaborated in some detail in this review.