Regarding electron transfer processes, a recent theory by Craven and Nitzan explored the implications of thermal non-homogeneity on length-scales comparable to the donor-acceptor distance on the electron transfer rate as well as heat transport. This theory, however, ignores vibrational contributions to the total heat conduction by assuming vibrational modes are localized near their corresponding centers. The same group of theoretical chemists at the University of Pennsylvania and Tel Aviv University addresses this gap, offering an updated unified theory of electron transfer (ET), ET-induced heat transport (ETIHT), and vibrational heat transfer. They present their work in The Journal of Chemical Physics.
The authors combine stochastic Langevin dynamics with Marcus-Levich ET theory, building on the Marcus-Levich concept of electron transfer in which system transitions between two electronic states – electron on donor and electron on acceptor – are assisted by energy exchanges with the system’s nuclear vibrational modes. Specifically, by advancing on the earlier Craven and Nitzan work, the authors’ model adds temperature modes Ta and Tb that consider heat transfer and friction forces within the Langevin equation.
After applying their theory in a system with two electronic sites and two vibrational modes, the researchers found that by tuning the coupling strength between donor-acceptor molecules within their local environments, they could increase the comparative magnitude of the ETIHT heat conduction over the phononic heat conduction in some multithermal ET reactions.
Looking forward, the authors explain that their theory may guide the design of experimental set-ups in which ETIHT and phononic heat could be compared. Lead author Renai Chen says, “we are excited because if our theory is verified in experiments, it will advance our understanding of molecular heat transport on the nanoscale.”
Source: “Electron-transfer-induced and phononic heat transport in molecular environments,” by Renai Chen, Galen T. Craven, and Abraham Nitzan, The Journal of Chemical Physics (2017). The article can be accessed at https://doi.org/10.1063/1.4990410.
