The reaction of HOD+ with N2O was studied over the collision energy (Ecol) range from 0.20 eV to 2.88 eV, for HOD+ in its ground state and in each of its fundamental vibrational states: bend (010), OD stretch (100), and OH stretch (001). The dominant reaction at low Ecol is H+ and D+ transfer, but charge transfer becomes dominant for Ecol > 0.5 eV. Increasing Ecol enhances charge transfer only in the threshold region (Ecol < 1 eV), but all modes of HOD+ vibrational excitation enhance this channel over the entire energy range, by up to a factor of three. For reaction of ground state HOD+, the H+ and D+ transfer channels have similar cross sections, enhanced by increasing collision energy for Ecol < 0.3 eV, but suppressed by Ecol at higher energies. OD stretch excitation enhances D+ transfer by over a factor of 2, but has little effect on H+ transfer, except at low Ecol where a modest enhancement is observed. Excitation of the OH stretch enhances H+ transfer by up to a factor of 2.5, but actually suppresses D+ transfer over most of the Ecol range. Excitation of the bend mode results in ∼60% enhancement of both H+ and D+ transfer at low Ecol but has little effect at higher energies. Recoil velocity distributions at high Ecol are strongly backscattered in the center-of-mass frame, indicating direct reaction dominated by large impact parameter collisions. At low Ecol the distributions are compatible with mediation by a short-lived collision complex. Ab initio calculations find several complexes that may be important in this context, and RRKM calculations predict lifetimes and decay branching that is consistent with observations. The recoil velocity distributions show that HOD+ vibrational excitation enhances reactivity in all collisions at low Ecol, while for high Ecol with enhancement comes entirely from the subset of collisions that generate strongly back-scattered product ions.
This work was supported by grants CHE-0647124 and CHE-1111935 from the Chemistry division of the National Science Foundation.
I. INTRODUCTION II. METHODOLOGY III. RESULTS A. Ground state cross sections B. Computational results C. Recoil velocity distributions D. Effects of HOD+ vibrational excitation IV. DISCUSSION A. Previous studies B. Ground state reaction mechanism C. Vibrational effects and the relative efficiency of different forms of energy 1. The charge transfer channel 2. H+/D+ transfer V. CONCLUSION