Integral cross sections for ${\mathrm{ArH}}^{+}$ production in the ${\mathrm{Ar}}^{+}$+${\mathrm{H}}_2$ reaction were measured by a novel high-resolution apparatus, at low collision energies (0.025–1 eV). The observed features are interpreted as due to successive openings of vibronic levels of the intermediate Ar-${\mathrm{H}}_2^{+}$ charge-transfer complex. The proposed potential-energy surfaces involve an accurate description of the entrance channels at long range including fine-structure and Σ-Π splitting effects.

• Received 26 February 1991

DOI:https://doi.org/10.1103/PhysRevLett.67.1254