Sachin Sharma

Separation of single-and two-center interference in ionization of H2 by proton impact

We present a triple differential experimental study of ionization of molecular hydrogen by proton impact. By comparing cross-sections obtained for coherent and incoherent projectile beams we were able to extract contributions from interference. Two types of distinctly different interferences could be identified. We demonstrate that both types can be separated in the same data set by analyzing triple differential cross-sections for fixed momentum transfer and for fixed recoil-ion momentum.

Triple Differential Study of Ionization of H 2 by Proton Impact for Varying Electron Ejection Geometries

We have performed a kinematically complete experiment on ionization of H2 by 75 keV proton impact. The triple differential cross sections (TDCS) extracted from the measurement were compared to a molecular 3-body distorted wave (M3DW) calculation for three different electron ejection geometries. Overall, the agreement between experiment and theory is better than in the case of a helium target for the same projectile. Nevertheless, significant quantitative discrepancies remain, which probably result from the capture channel, which may be strongly coupled to the ionization channel. Therefore, improved agreement could be expected from a non-perturbative coupled-channel approach.

Single- and two-centre effects in fully differential cross sections for single ionization of H2 molecules by 75keV protons

We present theoretical calculations of single ionization of H2 molecules by 75 keV proton impact. The computed fully differential cross sections for different electron ejection geometries and projectile kinematical conditions are compared with recent measurements made by Hasan et al (2014 J. Phys. B: At. Mol. Opt. Phys. 47 215201). We employ a molecular version of the continuum distorted wave-eikonal initial state model, where all the interactions present in the exit channel are considered on an equal footing. In addition, our approach allows us to incorporate different interference terms and to assess their influence. Overall, the agreement between experiment and theory is better than for the case of more sophisticated schemes for coplanar geometries.

Influence of the post-collision interaction on interference effects in ionization of H2 by proton impact

We have performed a kinematically complete experiment on ionization of H2 by 75 keV proton impact leading to electrons with a speed equal to the projectile speed. By comparing cross sections measured with a coherent and an incoherent projectile beam we were able to perform a detailed analysis of interference effects. We found that the interference structure is significantly more damped than for a smaller electron energy studied previously. This damping is further increased if kinematic conditions are selected which favor a strong role of the post-collisional interaction between the scattered projectile and the electron ejected to the continuum by a preceding primary interaction with the projectile.

Scattering-angle dependence of doubly differential cross sections for fragmentation of H{sub 2} by proton impact

We have measured double differential cross sections (DDCS) for proton fragment formation for fixed projectile energy losses as a function of projectile scattering angle in 75 keV p + H{sub 2} collisions. An oscillating pattern was observed in the angular dependence of the DDCS with a frequency about twice as large as what we found earlier for nondissociative ionization. Possible origins for this frequency doubling are discussed.

Fully differential study of ionization in p + H2 collisions near electron-projectile velocity matching

We have performed a kinematically complete experiment on ionization of H2 by 75 keV proton impact for electrons ejected with a speed close to the projectile speed. The fully differential data are compared to a three-body distorted wave and a continuum distorted wave—eikonal initial state calculation. Large discrepancies between experiment and theory, as well as between both calculations, are found. These probably arise from a strong coupling between the ionization and capture channels, which is not accounted for by theory.

Fully differential cross sections for ionization of H2 molecules by proton impact: single- and two-centre effects

Fully differential cross sections for ionization of H2 by 75 keV proton impact are compared with recent experimental data. Calculations were obtained by using a two-effective centre approximation within the CDW-EIS approach.

Effect of Projectile Coherence on Atomic Fragmentation Processes

We demonstrate that the projectile coherence can have a major impact on atomic fragmentation processes. This has been overlooked for decades in formal scattering theory and may explain puzzling discrepancies between theoretical and experimental fully differential cross sections for single ionization.