# Dexter electron transfer

The Dexter energy transfer rate, $k_{ET}$, is indicated by the proportionality
$k_{ET} \varpropto J \mathrm{exp}\left [ \frac{-2r}{L} \right ]$
where $r$ is the separation of the donor from the acceptor, $L$ is the sum of the Van der Waals radii of the donor and the acceptor, and $J$ is the spectral overlap integral defined by
$J = \int f_{\rm D}(\lambda) \, \epsilon_{\rm A}(\lambda) \, \lambda^4 \, d\lambda$