Based on quantum electrodynamics (QED), we propose a novel molecular radiation mechanism termed quantum electrodynamic non-adiabatic emission (QED-NAE). This process describes a type of radiation that arises from a non-adiabatic transition induced by electromagnetic vacuum fluctuations. Using 9-cyanoanthracene as an example, we combine quantum electrodynamics with first-principles calculations to evaluate its non-adiabatic emission rates in two different environments: a single-photon mode and vacuum containing infinitely many photon modes. Our theory clearly identifies three key factors that influence the QED-NAE process: the mode volume, the mass-weighted orientation factor, and the photonic density of states. Among these, the mode volume determines the coupling strength and serves as the dominant factor affecting the emission rate. In microcavities, strong coupling can significantly enhance the QED-NAE rate, whereas in free space, the weak coupling leads to a markedly lower rate. Furthermore, when extending from a single photon mode to infinitely many photon modes, the mass-weighted orientation factor contributes to an increase in the QED-NAE rate by approximately a factor of 8π/3. In free space, the photonic density of states follows a flat quadratic distribution, which slightly reduces the QED-NAE rate. Our results demonstrate that microcavities can substantially amplify non-adiabatic quantum electrodynamic effects, whereas such effects can be safely neglected in free space.
Figure 1. Schematic illustration of an electron–nuclear–photon coupled system in
(a) a single-photon mode and (b) infinitely many photon modes.
Figure 2. This study was selected as a cover article by the Journal of Chemical Physics.