Bottom-up analysis of rovibrational helical dichroism

We present a general theoretical framework for helical dichroism (HD), establishing an explicit link between chiral resolution and orbital angular momentum (OAM) exchange in light–matter interaction. Tracing microscopic mechanisms of the OAM transfer, we derive rotational selection rules, which establish that HD emerges only from the spin–orbit coupling of light, even for beams without the far-field OAM. Our findings refine the conditions for observing HD, provide a tool to re-examine the outcome of prior experiments, and guide future designs for chiral sensing with structured light.