Complete momentum balance in ionization of $H_2$ by 75-keV-proton impact for varying projectile coherence

We report on a kinematically complete experiment on ionization of $H_2$ by proton impact. While a significant impact of the projectile coherence properties on the scattering-angle dependence of double-differential cross sections (DDCSs), reported earlier, is confirmed by the present data, only weak coherence effects are found in the electron and recoil-ion momentum dependence of the DDCSs. This suggests that the phase angle in the interference term is determined primarily by the projectile momentum transfer rather than by the recoil-ion momentum. We therefore cannot rule out the possibility that the interference observed in our data is not primarily due to a two-center effect.

Figure 1

DDCSs for a fixed energy loss of 30 eV as a function of the projectile scattering angle θ. The closed and open data points were taken for the large and small slit distances, respectively.

Figure 2

DDCSs for a fixed energy loss of 30 eV as a function of the $x$ component of the recoil-ion (top) and electron (bottom) momentum. The closed and open data points were taken for the large and small slit distances, respectively.

Figure 3

DDCSs for a fixed energy loss of 30 eV as a function of the $y$ component of the electron. The closed and open data points were taken for the large and small slit distances, respectively.

Figure 4

DDCS for a fixed energy loss of 30 eV as a function of the $z$ component of the recoil-ion (top) and electron (bottom) momentum. The closed and open data points were taken for the large and small slit distances, respectively.

Figure 5

Ratio between the DDCSs of Fig. 2 for large and small slit distances for the electrons (open symbols) and recoil ions (closed symbols).

Figure 6

Ratio between the DDCSs for large and small slit distances as a function of scattering angle (closed symbols). The inset shows DDCSs as a function of the difference between the scattering angles measured directly and determined from the momenta of the target fragments. The open symbols show the ratio with the additional condition $\left|\Delta \theta \right|<0.15$ mrad (see text). The solid line shows the interference term of the form $1+\cos \left(q_t\Delta b\right)$ with $\Delta b=2$ a.u.