Research:

1. Relativistic Effects on the Angular Distribution of the Xe 5s PhotoelectronsScott B. Whitfield (Univ. of Wisconsin-Eau Claire),NSF-RUI 0244812 Research: In the absence of relativistic effects, the angular distribution parameter, β (which characterizes the emission angle of photoelectrons), of s-subshell electrons in closed-shell atoms will be a fixed value independent of the energy of the ionizing photons. When relativistic effects are important, e.g., the spin–orbit interaction, then energy dependent variations of β from the semiclassical value of 2.0 for s-subshell electrons can be expected even for closed-shell atomsbecause there will always be two outgoing partial waves which can interfere. In the case of s-subshell photoionization these are εp1/2 and εp3/2 partial waves. Hence, photo-ionization studies of s-subshells in closed-shell atoms provide an excellent testing ground for the investigation of relativistic effects because any deviation of the angular distribution of the s-subshell photoelectrons from β = 2.0 is necessarily due to dynamical differences between the εp1/2 and εp3/2 transition amplitudes. We examine the case of Xe 5s β parameter in the photon energy range from 80 – 280 eV [1]. This investigation was prompted by discrep-ancies between previous measurements [2 - 4] and between theory [5,6] and experiment. A comparison of our β results as a function of photon energy and previous experiments is shown in the figure below.

2. Relativistic Effects on the Angular Distribution of the Xe 5s PhotoelectronsScott B. Whitfield (Univ. of Wisconsin-Eau Claire),NSF-RUI 0244812 Broader Impacts: A co-author of this project [1] was an under-graduate, Joe Kane. His work in this project has given him an unprecedented exposure to cutting edge science using sophisticated equipment at a major national research facility (unusual for an undergraduate). Joe not only assisted in setting up and running the experiment, but was also involved in the data analysis. This exposed him to important techniques of data analysis applicable to any experimental science, not just physics, providing him with excellent preparation for a career as a scientist. [1] Whitfield SB, Kane J, Wehlitz R 2007 J. Phys.B 40 3647. [2] Hemmers O, Manson S T, Sant’Anna M M, Focke P, Wang H, Sellin I A and Lindle D W 2001 Phys. Rev. A 64 022507. [3] Sankari R, Ricz S,K¨ov´er A, Jurvansuu M,Varga D, Nikkinen J, Ricsoka T, AkselaH and Aksela S 2004 Program and abstracts 14th Int. Conf. on Vacuum Ultraviolet Radiation Physics (Th-Po-34) Cairns, Australia, 19–23 July) p 215 [4] Lagutin B M, Petrov I D, Sukhorukov V L, Whitfield S B, Langer B, Viefhaus J, Wehlitz R, Berrah N, Mahler W and Becker U 1996 J. Phys. B: At. Mol. Opt. Phys. 29 937. [5] Johnson W R and Cheng K T 2001 Phys. Rev. A 63 022504. [6] Toffoli D, Stener M and Decleva P 2002 J. Phys. B: At. Mol. Opt. Phys. 35 1275. In accord with the data of Ref. [3], on the high-energy side of the β minimum we observe a much slower riseback towards β = 2.0 than that observed by Hemmers et al [2]. In addition, our data show excellent agreement with the calcula-tions of Ref. [6] throughout the entire photon energy range. Our results, and previous exper-iments, clearly indicate that the RRPA calcula-tions [5] predict a larger deviation of β from 2.0 than what is observed. A comparison of our data and theory is shown below.