Extracting molecular axis alignment from photoelectron angular distributions

We present a procedure that will enable the extraction of molecular axis al ignment from evolving photoelectron angular distributions measured followin g (1+1) resonance-enhanced multiphoton ionization in which the first step p repares the initial alignment. This procedure is applicable to a picosecond time- and angle-resolved photoelectron spectroscopy experiment [such as th e one presented by Reid et al., J. Chem. Phys. 111, 1438 (1999)], and relie s on the radial dipole matrix elements for the ionization process having no time dependence on the time scale of the experiment. As an illustration, w e present a model calculation of the evolution of photoelectron angular dis tributions expected following the ionization of a prepared pure rotational wavepacket. (C) 2000 American Institute of Physics. [S0021-9606(00)00608-5] .