ChemInform Abstract: Imaging Atomic Orbital Polarization in Photodissociation

In the late 1980s, Dixon, Hall, Houston, Simons, and others recognized that experiments that probe the angular distribution of photofragments with spectroscopic techniques could be used to obtain the angular distribution of angular momentum polarization. These were generalized as “vector correlation” experiments, wherein one examines the correlations among the angular momentum polarization vector, the product recoil direction, the transition moment in the parent molecule, the laser polarization, the fluorescence polarization, or in scattering experiments, the relative velocity vector. Virtually all of the early studies were based on Doppler spectroscopy and emphasized rotational angular momentum polarization. Semiclassical models were used to interpret the experiments, largely, based on the bipolar harmonics approach introduced by Dixon. Around the same time, Chandler and Houston introduced the ion-imaging technique, in which the full recoil velocity distribution of stateresolved photofragments could be detected in a highly multiplexed approach. Soon thereafter, large orbital alignment effects in atoms were seen in imaging experiments, and it was immediately recognized that the semiclassical picture, developed to describe high-J rotational polarization, would not be suitable for interpretation of angular momentum polarization in atoms, and a new, fully quantum theory was required. The foundation for this theory was established in a paper in 1994 by Siebbeles et al. (see also the earlier paper by Vasyutinskii). The development of the theory is described fully in section 2.