Velocity dependence of the cross sections for Penning, rearrangement, and total ionization ofH2andD2molecules by He (2S3) and He (2S1) metastable atoms

The velocity dependence of both the Penning and rearrangement ionization cross sections ${\sigma }_{\mathrm{PI}}$ and ${\sigma }_{\mathrm{RI}}$ for ${\mathrm{H}}_2^{+}$ and He${\mathrm{H}}^{+}$ ion production, as well as total ionization cross section ${\sigma }_{\mathrm{TI}}$, resulting from the collisions of He ($2{}_{}{}^1{}_{}{}^{}S$) and He ($2{}_{}{}^3{}_{}{}^{}S$) with ${\mathrm{H}}_2$ is measured over the relative-velocity range 2400-5300 m/sec (0.04-0.20 eV energy range) in a crossed-beam experiment by a time-of-flight technique. Characteristic cross-section ratios $\frac{{\sigma }_{\mathrm{RI}}}{{\sigma }_{\mathrm{TI}}}$ and the relative magnitude of the cross sections ${\sigma }_{\mathrm{RI}}$, ${\sigma }_{\mathrm{PI}}$, and ${\sigma }_{\mathrm{TI}}$ are reported. Comparison with some recent theoretical calculations is made; we observe a fair agreement in the triplet case except for ${\sigma }_{\mathrm{RI}}$, but a strong difference in the singlet case.