| Description |
Ion molecule studies have not only determined reactivity of systems that would have otherwise been unavailable, but also provide a perspective that improves the understanding of the mechanisms that drive reaction. Presented here are studies of three ion molecule systems one of which is accompanied by an extensive set of direct dynamics trajectory calculations. In the first system presented, NO2 + in six different vibrational states was reacted with C2H2 over the center-of-mass energy range from 0.03 to 3.3 eV. The effects of the symmetric bend overtone (0200) excitation are particularly strong (factor of 4) while the delta overtone (0220) effects are much weaker. A large set of quasi-classical trajectories were calculated at the PBE1PBE/6-311G** level of theory, in an attempt to understand the mechanistic origins of this observation. The trajectories reproduce experiment where comparable. Analysis of these trajectories resolves the mechanistic origins of this vibrational effect. Similar experimental measurements were made for the first excited electronic state of this system where the charge is localized on the acetylene. The C2H2 + reactant was prepared in four distinct modes. Because both reactants have one unpaired electron,collisions can occur with either singlet or triplet coupling of these unpaired electrons, and the contributions the three channels (charge, O-, and O transfer) are separated based on distinct recoil dynamics. The effects of C2H2 + vibration are modest, but mode specific. Integral cross sections and product recoil velocity distributions were also measured for reaction of HOD+ with NO2, in which the HOD+ reactant was prepared in its ground state, and with mode-selective excitation in the 001 (OH stretch), 100 (OD stretch) and bend (010) modes. In addition, we measured the 300 K thermal kinetics in a selected ion flow tube reactor and report product branching ratios different from previous measurements. Reaction is found to occur on both the singlet and triplet surfaces with near unit efficiency. Origins of discrepancies in the thermal versus beam experiments are discussed. Nine mechanisms contribute to four product channels (proton, deuteron, charge, and O- transfer) with the contributions from each resolved. Vibrational effects allow determination of energy partitioning in proton and deuteron transfer reactions near the product ion dissociation threshold. |
