Polyatomic thermal radiative dissociation in microcavities

Blackbody Infrared Radiative Dissociation (BIRD) occurs when a molecule successively absorbs ambient thermal photons, climbing its vibrational ladder until a bond breaks. Infrared microcavities reshape this driving field by altering the electromagnetic density of states (DOS) and, under vibrational strong coupling (VSC), by engineering the polariton density of states (PDOS). Building on our recent diatomic BIRD framework, we generalize the theory to polyatomic molecules, incorporating full mechanical and electrical anharmonicities. By combining ab initio vibrational ladders with a master-equation BIRD kinetics model and effective polariton theories that include loss and disorder, we map regimes in which PDOS reshaping yields large, tunable changes in dissociation kinetics. Predicted signatures include oscillatory rate modulations with cavity length, sensitivity to Rabi splitting, and selective control of specific vibrational channels. These results establish DOS/PDOS engineering as a principled strategy to control unimolecular reactivity with infrared cavities, suggesting experimentally accessible pathways to control BIRD at room temperature.