A quantum-rovibrational-state-selected study of the proton-transfer reaction H(XΣ: 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.

Using the sequential electric field pulsing scheme for vacuum ultraviolet (VUV) laser pulsed field ionization-photoion (PFI-PI) detection, we have successfully prepared H(XΣ: 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 ≈ 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 H(XΣ: v; N) + Ne. Here, we present the integral cross sections [σ(v; N)'s] for the H(v = 1-3; N = 0-3) + Ne → NeH + H reaction observed in the center-of-mass kinetic energy (E) range of 0.05-2.00 eV. The σ(v = 1, N = 1) exhibits a distinct E 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 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.