  Photoelectron circular dichroism refers to the forward/backward asymmetry in
the photoelectron angular distribution with respect to the propagation axis of
circularly polarized light. It has recently been demonstrated in femtosecond
multi-photon photoionization experiments with randomly oriented camphor and
fenchone molecules [C. Lux et al., Angew. Chem. Int. Ed. 51, 5001 (2012);C. S.
Lehmann et al., J. Chem. Phys. 139, 234307 (2013)]. A theoretical framework
describing this process as (2+1) resonantly enhanced multi-photon ionization is
constructed, which consists of two-photon photoselection from randomly oriented
molecules and successive one-photon ionisation of the photoselected molecules.
It combines perturbation theory for the light-matter interaction with ab initio
calculations for the two-photon absorption and a single-center expansion of the
photoelectron wavefunction in terms of hydrogenic continuum functions. It is
verified that the model correctly reproduces the basic symmetry behavior
expected under exchange of handedness and light helicity. When applied it to
fenchone and camphor, semi-quantitative agreement with the experimental data is
found, for which a sufficient d wave character of the electronically excited
intermediate state is crucial.
