Light-Ion Charge Exchange in Atmospheric Gases

Measurements of the total charge-exchange cross sections of ${\mathrm{H}}^{+}$, $\mathrm{H}_2^{}{}_{}{}^{+}$, and ${\mathrm{He}}^{+}$ in ${\mathrm{N}}_2$, ${\mathrm{O}}_2$, C${\mathrm{O}}_2$, and ${\mathrm{H}}_2$O have been made, using a collision chamber to collect the slow collision products. An energy range from 40-1500 eV was examined. Except for protons incident on ${\mathrm{N}}_2$ and ${\mathrm{O}}_2$, the processes examined have cross sections which continue to rise at energies below 200 eV; some collision products were found to have energies of several eV. Excited states must be invoked to explain the observed results in terms of the adiabatic criteria. Comparisons with earlier work are given.