  Time-resolved photoemission orbital tomography (tr-POT) offers unique
possibilities for tracing molecular electron dynamics. The recorded
pump-induced changes of the angle-resolved photoemission intensities allow to
characterize unoccupied molecular states in momentum space and to deduce the
incoherent temporal evolution of their population. Here, we show for the
example of CuPc/Cu(001)-2O that the method also gives access to the coherent
regime and that different excitation pathways can be disentangled by a careful
analysis of the time-dependent change of the photoemission momentum pattern. In
particular, we demonstrate by varying photon energy and polarization of the
pump light, how the incoherent temporal evolution of the LUMO distribution can
be distinguished from coherent contributions of the projected HOMO. Moreover,
we report the selective excitation of molecules with a specific orientation at
normal incidence by aligning the electric field of the pump light along the
molecular axis.
