  There is recurrent interest in the orbital angular momentum (OAM) conveyed by
optical vortices, which are structured beams with a helically twisted
wavefront. Particular significance is attached to the issue of how, in its
interactions with matter, light conveying OAM might prove sensitive to the
relative handedness and degree of twist in the associated optical wavefront. As
a result of recent experimental and theoretical studies, the supposition that
beams with OAM might enable discrimination between oppositely handed forms of
matter has become a renewed focus of attention. Some of the tantalizing
conclusions that are beginning to emerge from this research have, however, not
yet established a definitive basis for a supporting mechanism. To resolve this
problem requires the development of theory to support a faithful
representation, and a thorough understanding, of the fundamental
molecule-photon physics at play in such optical processes, even for processes
as basic as absorption. The present analysis establishes mechanisms at play
that entail a novel manifestation of optical spin-orbit interactions (SOI),
engaging transition electric quadrupole moments. Moreover, powerful symmetry
principles prove to render distinctively different criteria governing the
exhibition of 2D and 3D chirality. The new results elucidate the operation of
such effects, identifying their responsibility for discriminatory optical
interactions of various forms in both chiral and achiral media.
