Quantifying electron correlation effects in ethanol decomposition pathways.

Ethanol decomposition is a prototypical multichannel organic reaction in which electron correlation plays a decisive role in determining activation barriers and reaction selectivity. We use fixed-node diffusion Monte Carlo (FN-DMC) to investigate three principal decomposition pathways: dehydration, C-C bond cleavage, and H2 elimination. The obtained results are compared with those from Hartree-Fock (HF), hybrid density functional theory (B3LYP), modified Gaussian-2 composite theory, and experimental kinetic data. By recovering the missing many-body correlation, FN-DMC lowers the HF forward activation barriers by 4-15 kcal mol-1 and yields barrier heights that are consistent with available Arrhenius activation parameters within expected thermal corrections. A correlation-energy analysis along the intrinsic reaction coordinate reveals a pathway-dependent modulation of dynamical correlation near the transition state, with the largest stabilization observed for the dehydration channel. The results demonstrate that FN-DMC provides a robust description of static activation barriers and offers mechanistic insight into the evolution of electron-correlation effects in complex bond-breaking reactions.