Complex formation, rearrangement, and reaction in PhOH++ND3: Vibrational mode effects, recoil velocities, and ab initio studies

Abstract

Vibrationally mode-selected phenol cations (C6H5OH+ and C6D5OH+) were reacted with ND3 in a guided-ion-beam instrument. Integral cross sections and recoil velocity distributions are reported as a function of collision energy and vibrational state. Three reactions are observed. A small signal is found for the [PhOH:ND3]+ adduct at low total energies, indicating the formation of a very long-lived complex. The major reaction is H/D exchange, generating PhOD++ND2H. Exchange is ∼40% efficient at low energies, strongly inhibited by collision energy, and strongly enhanced by excitation of PhOH+ vibrations. Recoil velocity distributions suggest that H/D exchange proceeds through a statistical complex at all energies. A precursor complex is invoked to explain the energy and vibrational state dependence. The endoergic proton transfer reaction is a minor channel at all energies, with dynamics intermediate between the direct and complex limits. Quantum chemistry and RRKM calculations are reported, providing an additional mechanistic insight.

Dynamical control of ‘statistical’ ion–molecule reactions

“…These are not isolated examples. Similar effects have been observed for other ion-molecule systems ranging in size from six atoms (e.g., OCS + + OCS [63]) to much larger systems such as reaction of C 6 H 5 OH + with NH 3 [64] or of acetaldehyde with a number of small molecules [65][66][67][68]. As in the examples presented, strong dynamical effects are observed even in reactions that are exoergic, with no activation barriers in excess of the reactant energy.…”

Effects of Collision and Vibrational Energy on the Reaction of CH3CHO+(ν) with C2D4

“…There, too, density of states and adiabaticity factors tend to suppress the higher-energy charge state. We note that for all the polyatomic ion−molecule reactions we have studied we see CT only in cases where the endoergicity is less than 1 eV. ,,,− ,− For this system, the CT endoergicity is only 0.28 eV, hence the substantial CT cross section, but the PT−HT energy difference is 1.1 eV.…”

“…For the exoergic ME and HT reactions, the distributions are not significantly different for the reaction of vibrationally excited reactants. An absence of significant vibrational effects on recoil velocity is typical for exoergic reactions of polyatomic ions, ,− and the reasons for the absence have been discussed recently . The effects of vibration on the endoergic CT channel are discussed below.…”

Vibrational effects on the reaction of NO2+ with C2H2: Effects of bending and bending angular momentum

“…In our approach to this problem, we use the effects of reactant vibrational excitation as a probe of the early time dynamics, based on the idea that the initial mode of excitation is scrambled by any strong perturbations, such as the formation of breaking of bonds. 1 Therefore, if significant mode-specific effects are seen, this implies that the rate-limiting step in the mechanism is early, and provides insight regarding which kinds of molecular motions are important. Product recoil velocity distributions probe reaction time scales and disposition of the available energy into the products, i.e., the middle and late stages of the mechanism.…”