Theoretical study of isomerization and dissociation transition states of C_3H_5O radical isomers: Ab initio characterization of the critical points and statistical transition-state theory modeling of the dynamics

摘要

I use coupled-cluster theory and a modest basis set, aug-cc-pVDZ, to calculate structures and harmonic vibrational frequencies of local minima and transition states on the C_3H_5O potential energy surface. Accurate energies are computed using explicitly correlated coupled-cluster methods and a large basis set, cc-pVQZ-F12, to approach the one-particle basis set limit. My computations characterize eight additional stable radical structures on the global potential energy surface for this system. Additionally, this study encompasses many more isomerization and dissociation pathways, both between previously known intermediates and ones first characterized here. Analysis of the transition states and statistical transition-state theory results shows that energetically small barriers connect many of the alkenol and epoxide intermediates to the straight-chain alkoxy isomers, leading to significant branching to these alkoxy radical intermediates. Facile isomerization to these alkoxy intermediates is significant because the barrier heights leading to H + acrolein and HCO + C_2H_4 product channels are energetically accessible even at low vibrational energies. The low dissociation barrier heights and loose transition states of these pathways result in unimolecular dissociation as opposed to isomerization to a different C_3H_5O intermediate.