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 (ΔElab ≈ 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 (Ecm) range of 0.05–2.00 eV. The σ(v+ = 1, N+ = 1) exhibits a distinct Ecm 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 Ecm 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.