Selective bond-breaking in molecules by intense infrared radiation

Selective breaking of molecular bonds by resonant infrared absorption has not been realized. This failure has been attributed to rapid redistribution of absorbed energy, which leads to a break of the weakest bonds. We report first-principles density-functional dynamical calculations for HCN that verify this conclusion for low intensities. At high intensities, however, the moleculeʹs response becomes highly nonlinear, the normal modes become irrelevant, and energy absorption at such frequencies is not particularly efficient. We find that the strong C–N bond breaks at an off-resonance frequency by a novel `concerted kickʹ mechanism.