Electronic energy transfer in near-resonant electron capture collisions of H₂⁺ with metal atoms: Radiative and nonradiative transitions

Modes of energy disposal in electron capture of H₂⁺ with metal atoms (Cs, K, Mg, and Zn) for ion velocities in the range 3-7 × 10⁷ cm/s are examined using combined optical and beam scattering techniques. Radiative and nonradiative transitions are observed for processes occurring under near resonant conditions. The following branching sequences are identified: Zn + H₂⁺(Χ ²∑ _g⁺) → Zn⁺ (4s, ²S) + H ₂ (b ³∑_u⁺) → 2H(1s, ²S) → Zn (4p, ¹P) + H₂⁺ (Χ ²∑_g⁺)→^hv Zn (4s ², ¹S), → H₂ (Χ ¹∑ _g⁺) + Zn⁺ (4p, ²P) →^hv Zn⁺ (4s, ²S), Mg + H₂ ⁺ (Χ ²∑_g⁺) → Mg ⁺ (3s, ²S) + H₂ (b ³∑ _u⁺) → 2H (1s, ²S) → H₂ (Χ ¹∑_g⁺) + Mg⁺ (3d, ²D) →^hv Mg⁺ (3p, ²P) →^hv Mg⁺ (3s, ²S) → H₂ (Χ ¹∑_g⁺), v″ = n) + Mg ⁺ (3p, ²P) →^hv Mg⁺ (3s, ²S), K (Cs) + H₂⁺ (Χ ²∑ _g⁺) → K⁺ (Cs⁺) + H₂ (a ³∑_g⁺) →^hv H₂ (b ³∑_u⁺) → 2H (1s, ²S) → K⁺ (Cs⁺) + H₂ (B ¹∑ _u⁺) →^hv H₂ (Χ ¹∑_g⁺) → K⁺ (Cs⁺) + H₂ (b ³∑_u⁺) → 2H (1s, ²S). Branching ratios are dependent on the vibrational state and the nuclear separation (Franck-Condon factors) of the H₂⁺ ion at the time of electron capture. The branching ratio decreases for the (triplet(/(singlet) formation for H₂ produced from reactions of vibrationally relaxed H₂⁺ ion with K or Cs. Under conditions of H₂⁺ ion relaxation, the kinetic energy of scattered atomic hydrogen following radiative decay from ³∑ _g⁺ state of H₂ increases, implying a shift in the ³∑_g⁺ → ³∑ _u⁺ continuum toward longer wavelengths. The results also show that, at these velocities, the reations occur under near-resonant conditions with vertical transitions.