Vibrational effect on charge-transfer processes in collisions ofH+andO+ions withC2H4molecules at energies below10keV∕u

Abstract

Charge-transfer processes in collisions of ${\mathrm{H}}^{+}$ and ${\mathrm{O}}^{+}$ ions with ${\mathrm{C}}_{2}{\mathrm{H}}_{4}$ molecules have been studied in joint theoretical and experimental approaches for collision energies below $10\phantom{\rule{0.3em}{0ex}}\mathrm{keV}∕\mathrm{u}$. Since H and O atoms possess nearly identical ionization potentials, these two ions are expected to share similar dynamics and hence to have similar cross-section values for charge transfer, at least for the energy region above $100\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. In the present experiments, these cross sections of ${\mathrm{H}}^{+}$ and ${\mathrm{O}}^{+}$ ions have been derived by the initial growth rate method in the energy range of $0.20\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}3.6\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$, while the present theoretical study has been carried out for ${\mathrm{H}}^{+}$ impact only. We have examined the vibrational effect on charge transfer, especially the ``temperature effect'' of the initial vibrational states of the ${\mathrm{C}}_{2}{\mathrm{H}}_{4}$ molecule as well as the final vibrational states of the product ${\mathrm{C}}_{2}{\mathrm{H}}_{4}^{+}$ molecular ion. Indeed, a strong influence of the initial vibrational states on charge transfer has been observed since these vibrationally excited initial and final states force the process to be more nearly resonant, thus making charge transfer more efficient. This vibrational effect, and perhaps rotational effect as well, that makes the collision process more nearly resonant has not been well investigated previously, and thus the present study is expected to shed much light on this effect in general.