Fully differential study of dissociative capture in P + H₂ collisions

In recent years, the key role of the projectile coherence properties has been studied in several ion-atom scattering processes. These studies strongly suggested that cross sections could be significantly affected by the projectile coherence properties, especially for fast, heavy ions. In the present study, we used such coherence effects as a tool to sensitively analyze the few- body dynamics of the scattering process. To this end, we performed three kinematically complete experiments on fragmentation of H2 by 75 keV proton impacts. A novel approach was used to analyze coherence and interference effects in the observed cross-sections. The idea was to measure cross sections for coherent and incoherent projectiles simultaneously under otherwise identical experimental conditions. In the first experiment, single electron capture accompanied by vibrational dissociation was studied. Fully differential cross-sections (FDCS) were extracted for a fixed kinetic energy release and for two different fixed molecular orientations as a function of scattering angle. The coherent to incoherent FDCS ratios, which represents the interference term, revealed two distinct types of interference, single- and two-center interference. In the latter, an unexpected phase shift of π was found in the pronounced oscillations observed in the interference term. In the other two experiments, single capture accompanied by excitation of the second electron to a repulsive state, and Coulomb explosion due to double capture were studied. No clear signatures of single-center interference were observed for either process. Two-center interference was identified for dissociative transfer excitation. No π phase shift was observed for this process. Only a very weak two-center interference structure at most was found for double capture --Abstract, page iv