Reactions of proton-bound dimers.

Area of Science:

• Physical Chemistry
• Chemical Kinetics
• Ion Molecule Reactions

Background:

• Proton-bound dimers are key intermediates in gas-phase ion chemistry.
• Understanding their thermal reaction pathways provides insights into intermolecular forces and reaction dynamics.

Purpose of the Study:

• To investigate the thermal reaction mechanisms of proton-bound dimers of acetonitrile, dimethyl ether, and acetone.
• To elucidate the role of dimer structure and base properties in dictating reaction outcomes.

Main Methods:

• Selected ion flow tube mass spectrometry was employed to study the thermal reactions.
• Analysis of reaction products identified association, switching, and proton transfer channels.

Main Results:

• Association reactions were observed exclusively for dimers with hydrogen-bonding bases (e.g., NH3, CH3OH).
• An association-insertion mechanism was proposed for symmetrically bound dimers, involving a central potential energy barrier.
• Ether-containing dimers, except for diethers forming bicyclic structures, did not exhibit insertion reactions.
• Dimers with peripheral hydrogen-bonding protons, like formic acid dimer, underwent switching reactions without insertion.

Conclusions:

• The presence of hydrogen-bonding protons is crucial for the association-insertion pathway in proton-bound dimers.
• Steric and electronic factors, including the potential for stable cyclic structures, influence the reactivity of ether-containing dimers.
• Reaction dynamics are governed by the dimer's potential energy surface, with central barriers affecting association rates.