Differential Charge-Transfer Cross Section for Collisions ofH+onO2

The angular distribution of fast hydrogen atoms from the exothermic reaction ${\mathrm{H}}^{+}$+${\mathrm{O}}_2$→H+$\mathrm{O}_2^{}{}_{}{}^{+}$ is measured for proton energies of 30-300 eV and scattering angles of 0-30°. By means of the known total cross section for this reaction, absolute differential cross sections are also derived. In spite of the relatively large energy defect of 1.5 eV, the distributions are found to be highly peaked in the forward direction. Theoretical implications of this result are discussed qualitatively. Measurements of the differential charge-exchange cross section of the system ${\mathrm{He}}^{+}$ + He showed good agreement with theoretical expectations.