Cooper minima and circular dichroism in photoelectron angular distributions

We demonstrate that circular dichroism in photoelectron angular distributions (CDAD), resulting from resonance enhanced multiphoton ionization (REMPI) of an aligned molecular Rydberg state, is a highly sensitive probe of the presence of a Cooper minimum near threshold. To illustrate this application of CDAD, we present the results of ab initio calculations for (1+1’) REMPI via the R 21(5.5) branch of the D ^2Σ^+(3pσ) state of NO, where a Cooper minimum is found in l=2 (d wave) of the kπ continuum at a photoelectron kinetic energy of 3.2 eV. The CDAD signal is found to vary rapidly with photoelectron kinetic energy, go through zero, and change sign in the region of the Cooper minimum. This result is predicted by CDAD theory for photoionization from an aligned atomic p orbital