Measurement of excited-state charge exchange reactions

A microwave-resonance optical detection technique has been used to study the charge exchange reaction in which 49-keV protons incident on nitrogen and hydrogen molecules form hydrogen atoms in the $n=3\mathrm{}$ state. Hydrogen atoms formed in the $n=3\mathrm{}$ state in the charge exchange cell pass through a radio-frequency field, and the Balmer-$\alpha$ light emitted by the atoms is monitored. Measurements are made with the microwave electric field both perpendicular and parallel to the direction of the proton beam and for light polarized both parallel and perpendicular to the beam direction. Through a detailed analysis of the observed resonances, the partial cross sections for capture into each of the angular momentum states ($L$ and $M_L$) are determined. The population of any state in the $n=3\mathrm{}$ manifold can be calculated from these cross sections.