Reaction of acetaldehyde cations with water: The effects of CH3CHO+ vibrational mode and impact parameter on reactivity and product branching

Abstract

Articles you may be interested inVibrational mode and collision energy effects on reaction of H 2 CO + with C 2 H 2 : Charge state competition and the role of Franck-Condon factors in endoergic charge transfer Scattering of mode-selectively excited acetaldehyde cations from D 2 O was studied in a guided ion beam instrument. The effects of reactant vibrational state and collision energy on reactivity, product branching, and product ion recoil velocity distributions were measured. Ab initio calculations were performed to help understand the reaction coordinate. The dominant reaction is H/D exchange, which occurs in about 40% of low energy collisions, dropping to just a few percent at high energies. H/D exchange is also inhibited by CH 3 CHO ϩ vibration, but with a smaller effect than the equivalent amount of collision energy. H/D exchange is mediated by a long-lived complex, and several candidates are identified. The other low energy channel corresponds to methyl elimination from the collision complex. This channel is the most energetically favorable, but is only a few percent efficient, even at low energies, and is negligible at high energies. Methyl elimination is strongly suppressed by both collision energy and vibration, and the vibrational effects are nonmode specific. The most interesting channel is proton transfer ͑PT͒, which occurs by a direct mechanism at all collision energies. At low energies, PT occurs only in small impact parameter collisions, while at high energies, PT occurs primarily for large impact parameters, and is suppressed for small impact parameters. PT also shows strongly mode-specific dependence on CH 3 CHO ϩ vibrational state.

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.…”

“…In other systems we have studied, for example, PhOH + + ND 3 19,20 and CH 3 CHO + + D 2 O, substantial H/D exchange is observed in hydrogen-bonded complexes. There are differences between the systems that account for the absence of H/D exchange in complex B for CH 3 CHO + + C 2 D 4 .…”

“…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.…”