A quantum-rovibrational-state-selected study of the proton-transfer reaction H2+(X2Σ +g: v+ = 1–3; N+ = 0–3) + Ne → NeH+ + H using the pulsed field ionization-photoion method: observation of the rotational effect near the reaction threshold

Abstract

Using the sequential electric field pulsing scheme for vacuum ultraviolet (VUV) laser pulsed field ionization-photoion (PFI-PI) detection, we have successfully prepared H₂⁺(X²Σ⁺_g: v⁺ = 1–3; N⁺ = 0–5) ions in the form of an ion beam in single quantum-rovibrational-states with high purity, high intensity, and narrow laboratory kinetic energy spread (ΔE_lab ≈ 0.05 eV). This VUV-PFI-PI ion source, when coupled with the double-quadrupole double-octupole ion–molecule reaction apparatus, has made possible a systematic examination of the vibrational- as well as rotational-state effects on the proton transfer reaction of H₂⁺(X²Σ⁺_g: v⁺; N⁺) + Ne. Here, we present the integral cross sections [σ(v⁺; N⁺)'s] for the H₂⁺(v⁺ = 1–3; N⁺ = 0–3) + Ne → NeH⁺ + H reaction observed in the center-of-mass kinetic energy (E_cm) range of 0.05–2.00 eV. The σ(v⁺ = 1, N⁺ = 1) exhibits a distinct E_cm onset, which is found to agree with the endothermicity of 0.27 eV for the proton transfer process after taking into account of experimental uncertainties. Strong v⁺-vibrational enhancements are observed for σ(v⁺ = 1–3, N⁺) in the E_cm range of 0.05–2.00 eV. While rotational excitations appear to have little effect on σ(v⁺ = 3, N⁺), a careful search leads to the observation of moderate N⁺-rotational enhancements at v⁺ = 2: σ(v⁺ = 2; N⁺ = 0) < σ(v⁺ = 2; N⁺ = 1) < σ(v⁺ = 2; N⁺ = 2) < σ(v⁺ = 2; N⁺ = 3), where the formation of NeH⁺ is near thermal-neutral. The σ(v⁺ = 1–3, N⁺ = 0–3) values obtained here are compared with previous experimental results and the most recent state-of-the-art quantum dynamics predictions. We hope that these new experimental results would further motivate more rigorous theoretical calculations on the dynamics of this prototypical ion–molecule reaction.