Fully differential cross sections for the single ionization of helium by fast ions: Classical model calculations

Abstract

Fully differential cross sections (FDCSs) have been calculated for the single ionization of helium by 1-and 3-MeV proton and 100-MeV/u C 6+ ion impact using the classical trajectory Monte Carlo (CTMC) method in the nonrelativistic, three-body approximation. The calculations were made employing a Wigner-type model in which the quantum-mechanical position distribution of the electron is approximated by a weighted integral of the microcanonical distribution over a range of the binding energy of the electron. In the scattering plane, the model satisfactorily reproduces the observed shape of the binary peak. In the region of the peak the calculated FDCSs agree well with the results of continuum-distorted-wave calculations for all the investigated collisions. For 1-MeV proton impact the experimentally observed shift of the binary peak with respect to the first Born approximation is compared with the shifts obtained by different higher-order quantum-mechanical theories and the present CTMC method. The best result was achieved by CTMC, but still a large part of the shift remained unexplained. Furthermore, it was found that the classical theory failed to reproduce the shape of the recoil peak observed in the experiments, it predicts a much narrower peak. This indicates that the formation of the recoil peak is dominated by quantum-mechanical effects. For 100-MeV/u C 6+ ion impact the present CTMC calculations confirmed the existence of the "double-peak" structure of the angular distribution of the electron in the plane perpendicular to the momentum transfer, in accordance with the observation, the prediction of an incoherent semiclassical model, and previous CTMC results. This finding together with wave-packet calculations suggests that the "C 6+ puzzle" may be solved by considering the loss of the projectile coherence. Experiments to be conducted using ion beams of anisotropic coherence are proposed for a more differential investigation of the ionization dynamics.

Classical Treatment of Aq+ + He Collisions

“…A shift of the CTMC binary peak was also present but was found to be twice smaller than that found using Fig. 4.33 Comparison of the FDCSs obtained by the present CTMC-SPM model (full red curve) for 1 meV proton impact in the scattering plane with the experimental data [25] (empty circles) and the predictions of quantum-mechanical models (blue curves) quantum mechanics. The recoil peak calculated with the CTMC method was smaller and narrower than that observed in the experiment and predicted by all the quantummechanical models.…”

“…Finally, very recently, the performance of the CTMC method was used to investigate for the ion-induced SI of He [25]. In this work, a Wigner type CTMC model was used in which the quantum-mechanical position distribution was approximated by a weighted integral of the microcanonical distribution of the binding energy of the electron.…”

“…The data are results of the present CTMC calculations using different approximations (for more details, see text) contrast, with more realistic wave functions (red dashed and full curves), the recoil peak appears. These wave functions are based on Roothann-Hartree-Fock (RHF) and Silverman-Platas-Matsen (SPM) position distributions [25]. In the following only the CTMC calculations using SPM wave functions are compared with experiment and quantum calculations.…”

Study of the Effect of Higher-order Dispersions on Photoionisation Induced by Ultrafast Laser Pulses Applying a Classical Theoretical Method

“…For our calculations we used the CTMC method originally introduced by Abrines and Percival to simulate ion collisions with H atoms 34 . Later CTMC was generalised for multielectron atoms 35 , and was proved to be a useful method to describe ion-atom collisions [36][37][38][39][40] . In the present work the applied screened potential for the electron-core interaction was chosen as…”

Study of the effect of higher-order dispersions on photoionisation induced by ultrafast laser pulses applying a classical theoretical method

“…For our calculations we used the CTMC method originally introduced by Abrines and Percival to simulate ion collisions with H atoms 34 . Later CTMC was generalised for multielectron atoms 35 , and was proved to be a useful method to describe ion-atom collisions 36 – 40 . Although numerous works dealing with soft-Coulomb potential 41 – 48 , as it was pointed out by Sarkadi 49 the screened potential 50 is in better agreement with the results obtained by quantum mechanical calculations.…”