Bottom-up Analysis of Ro-Vibrational Helical Dichroism

Helical dichroism (HD) is a proposed method for the resolution of molecular chirality, employing the orbital angular momentum (OAM) of light. Going beyond the conventional assumptions about HD, this work proposes a rigid theoretical framework for the analysis of the HD, based on molecular symmetries and rotational eigenstates. We derive the rotational selection rules, which clearly establish that HD only emerges from the spin-orbit coupling of light, even for beams without far-field OAM. Our findings refine the conditions for observing HD, shedding light on the outcome of prior experiments and guiding future designs for chiral sensing using structured light.