Quantum-vibrational-state-selected Integral Cross Sections and Product Branching Ratios for the Ion-molecule Reactions of N2 +(X2Σg +; v+ = 0–2) + H2O and H2O+(X2B1: v1 +v2 +v3 + = 000 and 100) + N2 in the Collision Energy Range of 0.04–10.00 eV

Abstract

Abstract By combining the vacuum ultraviolet laser pulsed field ionization-photoion (VUV-PFI-PI) ion source with the double quadruple-double octopole (DQDO) ion-guided mass spectrometer, we have investigated the center-of-mass collision energy (E cm) and vibrational-state dependences of the ion-molecule reactions of and and 100) + N2 covering the E cm range of 0.04–10.00 eV. The absolute integral cross sections (σ’s) for the charge transfer (CT) [σ CT(v +)] channel to form H2O+ and the H-atom transfer (HT) [σ HT(v +)] channel to form N2H+ from the reactions have been determined, revealing the dominance of σ CT(v +) over σ HT(v +) at E cm = 0.04–8.00 eV. The E cm dependence of σ CT(v +) at low E cm < 1.00 eV is consistent with the long-range ion-dipole and ion-induced dipole CT mechanism. Minor vibrational inhibition is observed for the σ CT(v +) at low E cm ≤ 0.30 eV, which can be rationalized by the near-resonance CT mechanism. While the σ HT(v +) values are consistent with previous measurements, the σ CT(v +) obtained here resolve a hump at E cm = 1.0–5.0 eV, which is not observed previously. This feature is attributed to the formation of excited H2O+(B 2 B 2) ions via the collision-assisted CT mechanism. The branching ratio for product H2O+[BR(H2O+)] is found to be constant (0.82 ± 0.05) at E cm = 0.04–1.00 eV, and is independent of v + vibrational state. As E cm is increased from 1.0 eV, the BR(H2O+) reaches a maximum of 0.93 at E cm ≈ 3.00 eV, followed by the decline to 0.20 at E cm ≥ 9.0 eV, where σ HT(v +) becomes dominant compared to σ CT(v +). The ) for the formation of N2H+ via the proton transfer (PT) channel of the H2O+(X 2 B 1: 000 and 100) + N2 reaction has also been measured. The comparison of the σ PT(000 and 100) values reveals significant (100) vibrational enhancement. Furthermore, the E cm thresholds determined here for σ PT(000 and 100) are in agreement with their thermochemical thresholds. The BR and σ values determined here are valuable for modeling the ion chemistry occurring in planetary atmospheres, in addition to serving as benchmarks for state-of-the-art quantum dynamics calculations.