Collisional studies of the excited state potential energy surfaces of HeH+2: Energy thresholds and cross sections for reactions of helium ions with hydrogen yielding H+, H+2, H+3, HeH+, and H*(n l)

Abstract

Beam collision cell apparatuses have been employed to determine the energy dependences of the cross sections for the reactions of He⁺ with H₂ to yield the ionic or luminescent product species H⁺, H⁺₂, H⁺₃, HeH⁺, H*(2l), H*(3l), and H*(4l). Distinct thresholds were observed for the formation of H⁺ at 7.1±0.2 eV, for HeH⁺ and H*(2l) at 9.0±0.1 eV, for H*(3l) at 12.7±1.0 eV, and for H*(4l) at 14.4±1.5 eV. The analogous reactions of He⁺ with D₂ have also been studied to confirm these results. Secondary thresholds were also detected, and some of the reactions exhibit apparent isotope effects. Polarization is shown not to appreciably affect the cross sections for H* formation. Both H⁺₂ and H⁺₃, but not HeH⁺ or H*, are observed as products at near thermal collision energies. The experiments which resulted in the detection of the products H₂⁺, H₃⁺, and especially HeH⁺, as well as the more precise studies of H⁺ formation, which are reported herein, were suggested by the theoretical analysis. These results demonstrate the enhancement value of an integrated experimental–theoretical approach for the study of state‐to‐state chemistry.