Investigation of projectile coherence effects in fully differential studies of 75 keV proton - H₂ collisions

Fully differential cross sections (FDCS) have been measured for single ionization of H2 by 75 keV proton impact with varying transverse coherence length of the projectiles. As reported in recent years, the scattering angle dependence of the doubly differential cross sections (DDCS) are significantly affected by the projectile coherence properties. The interference structures were observed for the coherent beam, however were absent for an incoherent beam. Interestingly, the FDCS measurements for fixed momentum transfer do not suggest significant differences between the coherent and incoherent cross sections. However, for the FDCS with fixed recoil-ion momentum, clear differences between the two has been established. This suggests that the momentum-transfer vector determines the phase angle in the interference term, which is the ratio between coherent and incoherent cross sections. Earlier, the phase angle entering in molecular two-center interference was believed to be determined by the recoil-ion momentum vector. Recently, a theoretical study was reported which acknowledges that the measured DDCS mentioned above are affected by projectile coherence effects, however, suggests that this should not be seen as wave-packet (de)coherence effect. While our data do not disprove this assertion entirely, this theoretical analysis did not pass an experimental test proposed by its authors and performed within the research project for this thesis --Abstract, page iv