Time-resolved photoelectron angular distributions: concepts, applications, and directions.

The use of photoelectron angular distributions (PADs) as a probe in short-pulse, pump-probe scenarios is reviewed. We focus on concepts, on the insight that can be gained through theoretical analysis, on applications, and on future opportunities. Time-resolved PADs are sensitive to both the time-evolving rotational composition of wavepackets and their time-evolving electronic symmetry. The former feature renders this observable a potential probe of molecular structure, intensity effects, and rotational perturbations. The latter feature renders the PAD a potential probe of radiationless transitions.