Fully differential study of dissociative single capture and Coulomb explosion through double capture in $p+{\mathrm{H}}_2$ collisions

We have measured fully differential cross sections for dissociative single capture and Coulomb explosion through double capture in 75 keV $p+{\mathrm{H}}_2$ collisions. Data were analyzed for fixed kinetic energy releases and molecular orientations as a function of scattering angle. Two-center interference was identified for dissociative single capture. The interference pattern is not inconsistent with the symmetry of the dissociative electronic state affecting the phase angle of the interference term. No clear signatures of single-center interference were observed for either process. For double capture at most only a very weak two-center interference structure was found. This very small (or zero) visibility can probably be attributed to a convolution of two independent scatterings of the projectile with the two electrons yielding the measured scattering angle.

Figure 1

Schematic diagram of the experimental set-up.

Figure 2

Time spectrum of coincidences between neutralized projectiles and molecular proton fragments (top panel) and ${\mathrm{H}}^{-}$ projectiles and molecular proton fragments (bottom panel).

Figure 3

Kinetic energy release (KER) spectrum coincident with ${\mathrm{H}}^{\circ }$ projectiles (open and closed circles) and with ${\mathrm{H}}^{-}$ projectiles (solid triangles). The open (closed) circles were recorded with a large (small) recoil-ion extraction voltage.

Figure 4

Illustration of the two molecular orientations for which fully differential cross sections were analyzed. The top panel shows the perpendicular and the bottom panel the parallel orientation (relative to the transverse component of the momentum transfer).

Figure 5

Fully differential cross sections (FDCS) for dissociative capture leading to $\mathrm{KER}=5-12\mathrm{eV}$ and a molecular orientation perpendicular to both the initial projectile beam axis and the transverse component of the momentum transfer as a function of scattering angle. The open (closed) symbols represent the data taken with an incoherent (coherent) projectile beam.

Figure 6

Same as Fig. 5, but molecular orientation is parallel to the transverse component of the momentum transfer.

Figure 7

Ratios between the FDCS for coherent and incoherent projectiles from Fig. 6 as a function of scattering angle. Dashed curve, two-center interference term expected for a gerade dissociative state; dotted curve, two-center interference term expected for an ungerade dissociative state; solid curve, sum of the dashed and dotted curves with weight factors of $f$ and 1 - $f$ for the geared and ungerade states, respectively. For $f$, see text.

Figure 8

Top panel: illustration of the angle ${\theta }_{\mathrm{q}}$ enclosed by the momentum transfer q and the projectile beam axis and of the angle ${\theta }_{\mathrm{mq}}$ enclosed by the molecular axis and q. Bottom panel: ratios of Fig. 7 plotted as a function of the angle between the molecular axis and the momentum transfer vector ${\theta }_{\mathrm{mq}}$ calculated with Eq. (2). Curves: same as in Fig. 7.

Figure 9

Same as Fig. 5 for double capture, but integrated over all KER.

Figure 10

Same as Fig. 6 for double capture, but integrated over all KER.

Figure 11

Same as Fig. 10, but KER fixed at 13 to 18 eV (top panel), 18–22 eV (center panel), and 22–27 eV (bottom panel).