Cross sections forH+and H atoms colliding with Li in the low-keV-energy region

Abstract

State-to-state, summed charge transfer and stopping cross sections in collisions of protons and neutral hydrogen atoms with lithium atoms have been studied at collision energies ranging from $10\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}25\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$. Cross sections were calculated using electron-nuclear dynamics (END), which is a nonadiabatic, time-dependent, direct approach for the study of ion-atom-molecule interaction processes. Our results show good agreement when compared to available theoretical and experimental data. We find that the charge transfer cross section for protons shows a bump and a maximum as a function of the projectile energy, both of them as a result of the large probability for capture into the projectile $2p$ orbital. The bump corresponds to a projectile energy of approximately ${E}_{p}\ensuremath{\sim}0.7\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$, and results from the electron capture probability in the low impact parameter region of approximately $b\ensuremath{\sim}2.0\phantom{\rule{0.3em}{0ex}}\mathrm{a.u.}$ The maximum occurs at ${E}_{p}\ensuremath{\sim}5\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ as a result of the larger capture probability in the intermediate impact parameter region near $b\ensuremath{\sim}8\phantom{\rule{0.3em}{0ex}}\mathrm{a.u.}$ A similar behavior is found for the electron loss cross section for hydrogen projectiles. We find that the beam charge fraction, for all the energies considered, is nearly neutral. We also find that the largest contribution to the stopping cross section is for impact parameters around $b\ensuremath{\sim}5\phantom{\rule{0.3em}{0ex}}\mathrm{a.u.}$ Finally, we report the total, electronic, and nuclear stopping cross sections to be within a factor of 2 of the reported values in the SRIM 06 code (SRIM stands for stopping and range of ions in matter) and other available experimental data. The largest discrepancy is due to the charge transfer process as well as to a transient $\mathrm{Li}{\mathrm{H}}^{+}$ molecular ion formed in the low projectile energy region.