Negligible Effect of Vibrational Polaritons on Chemical Reaction Rates via the Density of States Pathway

Abstract

We show that the polariton density of states in planar optical cavities strongly coupled to vibrational excitations remains much lower than the density of vibrational states even at the frequency of the lower and upper polaritons under most practical circumstances. The polariton density of states is higher within a narrow window only when the inhomogeneous line width is at least an order of magnitude smaller than the Rabi splitting. Therefore, modification of reaction rates via the density-of-states pathway appears small or negligible for the scenarios reported in the literature. While the polariton density of states is bounded from above by the freespace optical density of states in dielectric cavities, it can be much higher for localized phonon polariton modes of nanoscale particles. We conclude that other potential explanations of the reported reactivity changes under vibrational strong coupling should be examined.

Scouting for strong light–matter coupling signatures in Raman spectra

“…This unequivocally proves that Raman scattering to the levels arising from vibrational strong coupling effect has not been detected. The hybrid molecule-cavity systems contain many uncoupled molecules, or the so-called ''dark states'', [65][66][67] which are molecular vibrations that are not interacting or interacting weakly with the cavity mode. This is mainly caused by a mismatch between the orientation of the transition dipole moment and the electric field in the cavity.…”

Recent Progress in Vibropolaritonic Chemistry

“…In addition, a number of theoretical studies have been developed since the first observation of the VSC‐modified reaction kinetics. Many theoretical works continue to appear which do not predict appreciable reactivity change in experimentally relevant scenarios . Much work lies ahead before routine prediction of VSC‐modulated chemistry is possible.…”

Supramolecular Assembly of Conjugated Polymers under Vibrational Strong Coupling

“…In the last several years, it has been shown that coupling vibrational modes in this way has a pronounced effect on chemistry and molecular properties. [3,[5][6][7][8][9][10][11][12][13][14][15][16][17]20] In this vibrational strong coupling regime (VSC), vibro-polaritonic states (VP + , VPÀ) are formed, separated by the so-called Rabi splitting energy (" h W R ) (Figure 1 a). In typical experiments, a large number N of molecules are coupled by VSC to a single optical mode which leads to the formation of N-1 dark states (DS) which are, together with VP + and VPÀ, delocalized over many molecules.…”