PNNL

Abstract

A direct dynamics simulation at the B3LYP/6-311+G(d,p) level of theory was used to study the reaction dynamics of F- + CH3OOH collisions. The results of the simulations are in excellent agreement with a previous experimental study (J. Am. Chem. Soc. 2002, 124, 3196). Two product channels, HF + CH2O + OH- and HF + CH3 OO-, are observed. The former dominates and occurs via an ECO2 mechanism in which F- attacks the CH3- group, abstracting a proton. Concertedly, a carbon-oxygen double bond is formed and OH- eliminated. Somewhat surprisingly this is not the reaction path, predicted by the intrinsic reaction coordinate (IRC), following F- attack of the CH3- group. The IRC leads to a deep potential energy minimum for the CH2(OH)2 · · · F- complex which dissociates to F- + CH2(OH)2. None of the direct dynamics trajectories followed the IRC, leading to this minimum and product channel. This channel has an exothermicity of 60 kcal/mol, much lower than the 27 kcal/mol exothermicity for the observed channel. Other channels not observed and which have lower exothermicities are F-+CO+H2+H2O (43 kcal/mol) and F- + CH2O + H2O (51 kcal/mol). Formation of a CH3OOH· · ·F- complex, with randomization of its internal energy, is important. This complex dissociates via the ECO2 mechanism forming HF + CH2O + OH-. Trajectories which form HF + CH3OO- are non-statistical events and, for the 4 ps direct dynamics simulation, are not mediated by a CH3OOH· · · F- complex. Dissociation of this complex to form HF + CH3OO- may occur on longer time scales.