Longitudinal Recoil Ion Momentum Distributions for proton-argon ionizing collisions at intermediate energies

S. OTRANTO; R. E: OLSON

Kalamazoo, Michigan

Conferencia; XXVI INTERNATIONAL CONFERENCE ON PHOTONIC, ELECTRONIC AND ATOMIC COLLISIONS; 2009

Synopsis Proton-argon ionizing collisions at intermediate energies are studied by means of the classical trajectory Monte Carlo method (CTMC). In particular, we focus on the longitudinal and transverse recoil momentum distributions for the process. We compare the profile of the longitudinal momentum distribution at the abrupt rise region corresponding to the electron capture to the continuum (ECC) processes, with those obtained for simpler targets like H and He. Selected subsets of the data show that the recoiling multielectronic ion plays a major role in the low energy electron emission, influencing the angular asymmetry of the electronic emission. During the last decade, the development of the COLTRIMS technique allowed the investigation of several collisional systems in a way that could have been hardly foreseen in previous years. By using this technique it was soon realized that the longitudinal momentum acquired by the recoil exhibits an abrupt rise in its profile which can be associated to the ECC processes [1,2]. Furthermore, capture and capture plus excitation channels also leave a trace in the recoil’s longitudinal distribution providing a set of discrete peaks which can be experimentally resolved [2]. In this work, we use the CTMC method to study proton collisions on argon atoms at intermediate collision energies. The recoil and emitted electron momentum distributions are presented and selected subsets of the data corresponding to electrons emitted with very low energy are particularly analyzed. A central potential derived from Hartree-Fock wave functions is used for the electron-core interaction. In Figure 1, we observe the longitudinal momentum distribution of the Ar+ ions and the emitted electrons for 100 keV proton impact collisions. The cutoff located at approximately -0.7 a.u. is clearly visible for the recoil ion. Furthermore, it can be seen that instead of a single maximum structure as observed for He targets [2], the present system exhibits a maximum at 0.2 a.u. with a clear shoulder at about -0.3 a.u. which are possibly due to the interaction with the multielectronic core. We also analyze partial subsets of the shown data from which we infer that low energy emitted electrons are not only related to large impact parameter collisions but also to collisions involving a large momentum exchange with the recoiling Ar+ ion. Singly differential cross sections in angle are also studied and clearly reveal such a trend. -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 0.00E+000 1.00E-016 2.00E-016 3.00E-016 4.00E-016 5.00E-016 6.00E-016 ds/dpz (cm2/a.u.) pz (a.u.) recoil electron Fig. 1. Longitudinal momentum distributions for 100 keV proton-argon ionizing collisions. Work at UNS supported by PGI 24/F038, PICT- 2007-00887 (ANPCyT) and PIP 112-200801- 02760 (CONICET). References [1] Rodriguez V et al. 1995 Phys. Rev. A 52 R9. [2] Weber Th. et al. 2001 Phys. Rev. Lett. 86 224 1E-mail: sotranto@uns.edu.ar 2E-mail: olson@mst.edu XXVI International Conference on Photonic, Electronic and Atomic Collisions IOP Publishing Journal of Physics: Conference Series 194 (2009) 082014 doi:10.1088/1742-6596/194/8/082014 c