  Light-induced charge transmission through a molecular junction (molecular
diode) is studied in the framework of a HOMO-LUMO model and in using a kinetic
description. Expressions are presented for the sequential (hopping) and direct
(tunneling) transient current components together with kinetic equations
governing the time-dependent populations of the neutral and charged molecular
states which participate in the current formation. Resonant and off-resonant
charge transmission processes are analyzed in detail. It is demonstrated that
the transient currents are associated with a molecular charging process which
is initiated by photo excitation of the molecule. If the coupling of the
molecule to the electrodes is strongly asymmetric the transient currents can
significantly exceed the steady state current.
