Stereodynamical control of product branching in multi-channel barrierless hydrogen abstraction of CH₃OH by F

Abstract

Comprehensive dynamical simulations of a prototypical multi-channel reaction on a globally accurate potential energy surface show that the non-statistical product branching is dictated by unique stereodynamics in the entrance channels.

Comprehensive Investigations of the Cl + CH 3 OH → HCl + CH 3 O/CH 2 OH Reaction: Validation of Experiment and Dynamic Insights

“…Two potential wells, namely the reactant complex (RC1, −5.60 kcal/mol) and product complex (PC1, 0.65 kcal/ mol), 26,49 are found to flank TS1, with geometries similar to those in F + CH 3 OH → HF + CH 3 O, which has a submerged barrier and large exoergicity. 22,24,25 The RC1 well is quite deep, presumably stabilized by a two-center-threeelectron hemi-bond formed between the unpaired electron of the Cl atom and a lone pair of the O atom. 26,73 In the other channel to CH 2 OH and HCl (R2), TS2 is a submerged saddle point, −0.72 kcal/mol below the reactant asymptote.…”

“…Although the geometry of TS2 resembles that in F + CH 3 OH → HF + CH 2 OH, the configuration of RC2 is rather different. 22,24,25 In the latter, F is located at the end of the CH 3 moiety with nearly three equivalent F-H distances. For RC2 of the current system, Cl is located between OH and CH 3 .…”

“…The complex temperature dependence of the rate coefficient is quite common for barrierless reactions with a prereaction well. 25,67,74…”

“…Unlike the F + CH 3 OH reaction where corresponding pathways are both barrierless, [21][22][23][24][25] the barrierless R2 channel dominates in low temperatures due to a significant barrier in R1. 26,27 Indeed, experimentally, the branching ratio of R2 has been determined to be close to unity up to 500 K. 18 Various techniques have been employed to study the kinetics of R2 over the temperature range of 200-600 K. 18,19,[27][28][29][30][31][32][33][34][35][36][37][38][39] Although there are significant inconsistencies among these measurements, it is clear that the reaction is fast and the temperature dependence of the thermal rate coefficient is not Arrhenius, signaling complex kinetics.…”

Stereodynamical Control of Nonadiabatic Quenching Dynamics of OH(A2S+) by H2: Full-Dimensional Quantum Dynamics

“…[43][44][45] In an activated reaction, the access of the reactive transition state is often facilitated by a cone of acceptance, 46 which in uences not only the reactivity, but also product state distributions 47 and sometimes product branching. 48 It follows that stereodynamics could also have a signi cant impact on nonadiabatic dynamics, although such examples in collision processes are few and far between. 49,50 The nonadiabatic quenching process discussed here serves as an excellent example for nonadiabatic barrierless scattering between molecular reactants.…”