Small-angle scattering of hydrogen atoms and protons in various gases

Cross sections have been measured for the differential (in angle) scattering of 15-keV ${\mathrm{H}}^{+}$ and ${\mathrm{H}}^0$ in targets of He, Ar, ${\mathrm{H}}_2$, and ${\mathrm{N}}_2$. Separate cross sections are presented for scattering projectiles in the singly charged (${\mathrm{H}}^{+}$), neutral (${\mathrm{H}}^0$), and negatively charged (${\mathrm{H}}^{-}$) states; scattering angles range from 0.5 to 10 deg. Summing these constituent cross sections we arrive at a "total" cross section for scattering all projectiles into a particular angle. This "total" differential cross section is compared with predictions using a simple screened Coulomb potential; for the molecular targets the cross section is taken to be twice that for the corresponding atom. For ${\mathrm{H}}^{+}$ and ${\mathrm{H}}^0$ impact on He and ${\mathrm{H}}_2$ the measured cross section agrees with the predicted value; in these cases the effect of screening is negligible. For ${\mathrm{H}}^{+}$ and ${\mathrm{H}}^0$ impact on Ar and ${\mathrm{N}}_2$ the measurements agree fairly well with the screened Coulomb calculation at angles up to 1.5 deg and then fall lower than the predictions at larger angles; theory and experiment differ by a factor of two at 10 deg in one case. For all cases considered the formation of scattered ${\mathrm{H}}^{-}$ ions occurs in less than 2% of the collision events.