Mass-analyzed threshold ionization (MATI) has been used to prepare phenol cations in selected vibrational states, including the ground state. Reactions of ground state C6H5OH+ with ND3, studied in a guided ion-beam apparatus, are reported, along with related ab initio calculations. This paper focuses on the energetics and product branching in the proton transfer (PT) channel. Based on thermochemistry in the literature, combined with calculations of the intracomplex PT barrier, PT was expected to make up a large fraction of the total reactive scattering. Experimentally, it is found that PT has a small cross section with clear threshold behavior, and the conclusion is that the PT reaction is endoergic by 4.5±1 kcal/mole. Assuming that NH3 has a proton affinity of 204.0 kcal/mole, this results in a proton affinity for phenoxy radical of 208.7 kcal/mole, and a neutral PhO–H bond energy of 91.1 kcal/mole. The results are used to reinterpret previous dissociative photoionization studies of phenol-ammonia complexes.

The effects of NO+ rotational state and collision energy on the reaction NO++C2H5OH→HNO+C2H4OH+ were studied in a guided-ion-beam instrument over the collision energy range from 50 meV to 3.7 eV. Integral cross sections for the reaction are presented. NO+ is prepared in specific rotational levels (N+=0,1 and N+=10) by means of mass-analyzed threshold ionization. Ab initio calculations were used to probe stationary points on the potential energy surface. The reaction is sharply inhibited by collision energy, suggesting a bottleneck for reaction. If rotational energy had a similar effect, ∼50% inhibition from N+=10 excitation would be observed at low collision energy. Instead, rotation is found to have no effect within experimental error. A precursor complex mechanism is proposed to explain the results.

REMPI spectra are reported for the acetaldehyde Ã 1A″, B̃, C̃, and D̃ states. Photoelectron spectroscopy is used to probe the nature of the intermediate states, measure the cation vibrational frequencies, and to identify useful routes for preparing state-selected ions. Ab initio calculations of neutral and cation vibrational frequencies are also reported. The B̃ state is found to be a well-behaved Rydberg state, but with some distortion relative to the cation geometry along the ν10 and ν15 coordinates. There are B̃ state REMPI transitions that produce well state-selected cations, with vibrational energies of up to 0.4 eV, and several new cation frequencies are observed. The Ã 1A″ state gives structured, if somewhat broadened, REMPI transitions, but ionizes to produce a broad population of vibrationally hot ions. Only the origin band of the C̃ state is observed in REMPI, despite high intensity for this state in absorption. A few D̃ state transitions are sharp, and ionize to produce cold cations, as expected for a good Rydberg state. Most D̃ state levels are strongly mixed and broadened, however, and ionize to hot cations. Inconsistencies in the literature are discussed in light of the photoelectron spectra and ab initio results.

The reaction of acetaldehyde cations with ethene has been studied as a function of collision energy and acetaldehyde vibrational state. REMPI through different vibrational levels of the B̃ electronic state is used to produce CH3CHO+ with controlled excitation in different vibrational modes. Reactions are studied in a guided ion beam instrument, including measurements of product ion recoil velocity distributions. In addition, we calculated the structures and energetics of 13 different complexes that potentially could serve as intermediates to reaction. Three reactions are observed. Hydrogen atom transfer (HT) dominates at low collision energies and is suppressed by collision energy and, to a lesser extent, vibration. The HT reaction is clearly direct at high collision energies but appears to be mediated by a reactant-like precursor complex at low energies. The most energetically favorable product channel corresponds to elimination of CH3 from an intermediate complex. Nonetheless, this channel accounts for only ∼0.5% of the total product signal. The cross section for endoergic charge transfer (CT) is strongly enhanced by collision energy in the threshold region. Over a wide range of collision and vibrational energy, CH3CHO+ vibrational excitation enhances CT, but only 18% as much as for the equivalent amount of collision energy. This effect is interpreted in terms of competition between the CT and other product channels. The expected proton-transfer channel is not observed, an absence also attributed to competition.

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.