Collective Vibrational Strong Coupling Effects on Molecular Vibrational Relaxation and Energy Transfer: Numerical Insights via Cavity Molecular Dynamics Simulations**

Abstract

Forasmall fraction of hot CO 2 molecules immersed in aliquid-phase CO 2 thermal bath, classical cavity molecular dynamics simulations show that forming collective vibrational strong coupling (VSC) between the C = Oasymmetric stretch of CO 2 molecules and ac avity mode accelerates hot-molecule relaxation. This acceleration stems from the fact that polaritons can be transiently excited during the nonequilibrium process, which facilitates intermolecular vibrational energy transfer. The VSC effects on these rates 1) resonantly depend on the cavity mode detuning, 2) cooperatively depend on Rabi splitting,a nd 3) collectively scale with the number of hot molecules.F or larger cavity volumes,t he average VSC effect per molecule can remain meaningful for up to N % 10 4 molecules forming VSC.M oreover,t he transiently excited lower polariton prefers to relax by transferring its energy to the tail of the molecular energy distribution rather than distributing it equally to all thermal molecules.Asfar as the parameter dependence is concerned, the vibrational relaxation data presented here appear analogous to VSC catalysis in Fabry-PØrot microcavities.

Cavity catalysis: modifying linear free-energy relationship under cooperative vibrational strong coupling

“… 35 A very recent approach in this direction is the non-equilibrium behavior of VSC. 30 Some recent reviews cover detailed discussion about the nature of vibro-polaritonic states and their applications. 1–4 Even though there are significant attempts on the theoretical side, a general mechanism of polariton chemistry is not well understood.…”

Polariton relaxation under vibrational strong coupling: Comparing cavity molecular dynamics simulations against Fermi's golden rule rate

“…In order to further include the effect of cavity loss, during the nonequilibrium simulation, we attach a Langevin thermostat to the cavity mode only 53 . Here, the friction lifetime of the Langevin thermostat defines the inverse of the cavity loss rate.…”

“…Our approach for studying polariton relaxation is classical cavity molecular dynamics (CavMD) simulations 45,[52][53][54] , in which both the cavity modes and molecular vibrations are treated classically and move along an electronic ground state surface. Compared with standard theories for strong light-matter interactions, CavMD has two advantages: the ability to (i) describe realistic molecules and (ii) treat a very large number of molecules coupled to the cavity with an affordable computational cost.…”

“…We note that recent considerations of the role of VSC played by symmetry and selection rules can in princi- Selectively exciting solute molecules via solvent polariton pumping 54 . (e) Dark-mode relaxation and energy transfer dynamics 53 . The cartoon in the middle circle demonstrates the simulation setup of CavMD, which is adapted from Ref.…”

“…(e) Nonequilibrium dark-mode dynamics 53 . For a small fraction of hot CO 2 molecules immersed inside a CO 2 thermal bath, in the absence of external pumping, the LP can be transiently excited even when the molecular system size is large.…”