Photoelectron angular distributions (PADs) for O 1s, C 1s and S 2p 1/2, 2p3/2 ionization of OCS molecules have been measured in shape resonance regions. These PAD results are compared with the results for O 1s and C 1s ionization of CO molecules, and multi-scattering Xα (MSXα) calculations. The mechanism of the PAD formation both for parallel and perpendicular transitions differs very significantly in these molecules and a step from a two-centre potential (CO) to a three-centre potential (OCS) plays a principal role in electron scattering and the formation of the resulting PAD. For parallel transitions, it is found that for the S 2p and O 1s ionization the photoelectrons are emitted preferentially in a hemisphere directed to the ionized S and O atom, respectively. In OCS O 1s ionization, the S-C fragment plays the role of a strong 'scatterer' for photoelectrons, and in the shape resonance region most intensities of the PADs are concentrated on the region directed to the O atom. The MSXα calculations for perpendicular transitions reproduce the experimental data, but not so well as in the case of parallel transitions. The results of PAD, calculated with different ℓ max on different atomic centres, reveal the important role of the d (ℓ ≤ 2) partial wave for the S atom in the partial wave decompositions of photoelectron wavefunctions.
|Number of pages
|Journal of Physics B: Atomic, Molecular and Optical Physics
|Published - 2005 Oct 28