Single electron capture by multiply chargedSi28ions in atomic and molecular hydrogen

Cross sections for single electron capture by ${\mathrm{Si}}^{q+}$ ($2\le q\le 9$) incident on atomic and molecular hydrogen have been measured in the relative-collision-velocity range (3.1-6.3)×${10}^8$ cm/s. All measured cross sections decrease monotonically with relative velocity and scale roughly as $q^N$. The values of $N$ needed to fit the data range from ∼2 to ∼3 and increase with velocity. Cross sections averaged over incident charge states $q$ for molecular hydrogen are larger than for atomic hydrogen, becoming twice as large for relative velocities greater than 4×${10}^8$ cm/s. For the limited cases where comparison was possible, we found the classical-trajectory Monte Carlo calculation to give a good account of the experimental results.