Self-Dissociation of Polar Molecules in a Confined Infrared Vacuum

Coherent light-matter interaction of molecular media in infrared (IR) cavities is a promising tool for manipulating and controlling chemical reactivity and light emission. We study the wavepacket dynamics of a single hydrogen fluoride (HF) molecule in electromagnetic environment, using the multiconfiguration time-dependent Hartree (MCTDH) method. We show that in the absence of additional thermal or coherent external sources, a single-mode cavity vacuum can efficiently dissociate a HF bond that is suddenly prepared in the vibrational ground level. We predict dissociation probabilities of up to 20% in less than 200 fs for a bare vacuum field that is resonant with the fundamental vibration frequency at the onset of the ultrastrong coupling regime. Additional enhancements of the dissociation probability can be expected for cavity with thermal excitations and multimode cavities. The results are understood analytically as the result of a Bloch-Siegert shift by using the extended-multi-level quantum Rabi model in a polaron frame that highlights the influence of the permanent dipole moments in the light-matter dynamics. Our work highlights the fundamental differences that can be expected for reactive dynamical processes inside infrared cavities and plasmonic nanostructures relative to free space.