Reactions of Fe− with acids: gas-phase acidity and bond energy of FeH

Abstract

Kinetics and products for the gas-phase reactions of Fe− with the acids CH 3C(O)CH 2C(O)CH 3, HCO 2H, CH 3CO 2H, CH 3CH 2CO 2H, and H 2S have been determined using a selected-ion flow drift tube. Electron detachment is the sole reaction channel for reaction with CH 3C(O)CH 2C(O)CH 3, CH 3CO 2H, and CH 3CH 2CO 2H, and a dominant reaction channel for reaction with HCO 2H and H 2S. Proton transfer from HCO 2H to Fe− occurs and was studied as a function of increasing kinetic energy. These reactions are used to determine δ H° acid,298 (FeH) = 345.2 ± 4.4 kcal mol− 1, which determines the homolytic bond energy D° 298(Fe−H) = 35.1 ± 4.4 kcal mol −1. The electron detachment reactions and reactions leading to ion products in reactions with HCO 2 H and H 2S are discussed in view of the available thermochemistry. A mechanism involving initial proton transfer within the collision complex is suggested for all reactions.