Few-Body Dynamics Underlying Postcollision Effects in the Ionization of H₂ by 75-KeV Proton Impact

We have measured fully differential cross sections (FDCS) for ionization in 75-keVp+H2 collisions for ejected electron speeds close to the projectile speed. The data were analyzed in dependence on both the electron emission angle and the projectile scattering angle. Pronounced postcollisional effects between the projectile and the ejected electrons were observed. Significant differences between experiment and theory and between two conceptually very similar theoretical models were found. This shows that in the region of electron-projectile velocity-matching the FDCS is very sensitive to the details of the underlying few-body dynamics

Two-Center And Path Interference In Dissociative Capture In P+ H2 Collisions

We have measured and calculated fully differential cross sections (FDCS) for dissociative capture in 75-keV p+H2 collisions. FDCS were analyzed in the kinetic energy release (KER) ranges 0 to 2.1 eV and 4 to 7 eV for two different molecular orientations. In the latter range, dissociation is dominated by electronic excitation to the 2pπu state. Here, we observed two-center interference for an orientation in the plane perpendicular to the initial beam axis and parallel to the transverse momentum transfer. The interference pattern is afflicted with a constant phase shift of π. In the range KER=0 to 2.1 eV, dissociation is dominated by vibrational excitation. Here, we observed structures in the KER dependence, which we interpret as interference between two different paths of the molecular fragments during the dissociation

Fully Differential Investigation of Two-Center Interference in Dissociative Capture in p + H₂ Collisions

We have measured and calculated fully differential cross sections for vibrational dissociation following capture in 75-keV p + H2 collisions. For a molecular orientation perpendicular to the projectile beam axis and parallel to the transverse momentum transfer we observe a pronounced interference structure. The positions of the interference extrema suggest that the interference term is afflicted with a phase shift which depends on the projectile scattering angle. However, no significant dependence on the kinetic-energy release was observed. Considerable discrepancies between our calculations and experimental data were found

Target Dependence of Postcollision Interaction Effects on Fully Differential Ionization Cross Sections

We have measured and calculated fully differential cross sections (FDCS) for ionization of helium by 75-keV proton impact. Ejected electrons with a speed close to and above the projectile speed were investigated. This range of kinematics represents a largely unexplored regime. A high sensitivity of the FDCS to the details of the description of the few-body dynamics, reported earlier for ionization of H2, was confirmed. A peak structure was found in an electron angular range between the regions where the so-called binary and recoil peaks are usually observed. The need for nonperturbative calculations using a two-center basis set is demonstrated

Target Dependence of Post-Collision Effects in Ionization by Proton Impact

We have measured and calculated double differential cross sections for ionization of Ne and Ar by 75 keV proton impact for a broad range of fixed projectile energy losses as a function of scattering angle. Along with data obtained previously for lighter targets this made possible a systematic analysis of post-collision effects between the scattered projectile and the continuum electron in the exit channel as a function of the target ionization potential. The data are consistent with an increasing strength of such effects with increasing ionization potential. However, second-order effects involving the projectile--residual target ion interaction also play an important role

Ejected-Electron-Energy and Angular Dependence of Fully Differential Ionization Cross Sections in Medium-Velocity Proton Collisions with He and H₂

We have measured fully momentum-analyzed recoiling target ions and scattered projectiles, produced in ionization of He and H2 by 75 keV proton impact, in coincidence. The momentum of the ejected electrons was deduced from momentum conservation. From the data we extracted fully differential ionization cross sections as a function of the polar electron emission angle (for fixed electron energies) and as a function of the electron energy (for fixed electron emission angles). Comparison between experiment and various distorted wave calculations confirms that under kinematic conditions where the post-collision interaction plays an important role, the few-body dynamics underlying the ionization process are still poorly understood