Ab Initio Kinetics for Decomposition/Isomerization Reactions of C₂H₅O Radicals

Abstract

Radical reactions: The ground-state potential energy surface of the C(2)H(5)O system is investigated by ab initio methods using optimized geometries. The rate constants for the unimolecular isomerization and decomposition reactions of the three isomeric radicals (see picture) are calculated by microcanonical transition-state theory at 200-3000 K, varying the pressures of the diluents.The ground-state potential energy surface of the C(2)H(5)O system, including the decomposition and isomerization of the ethoxy (CH(3)CH(2)O), 1-hydroxyethyl (CH(3)CHOH), and 2-hydroxyethyl (CH(2)CH(2)OH) radicals, is computed by the modified Gaussian-2 (G2M) and CCSD(T)/6-311+G(3df,2p) methods by using the geometries optimized at the B3LYP/6-311+G(3df,2p) level of theory. These detailed reaction pathways are used to calculate the rate constants for the unimolecular isomerization and decomposition reactions of the three radicals by the microcanonical transition-state theory and Rice-Ramsperger-Kassel-Marcus (RRKM) theory in the temperature range of 200-3000 K at varying pressures of He and other diluents. The predicted rate constants are in reasonable agreement with the available experimental data. In addition, the predicted heats of formation of the three isomeric radicals are compared with available experimental and theoretical values.

Master Equation Modeling of the Unimolecular Decompositions of α‐Hydroxyethyl (CH3CHOH) and Ethoxy (CH3CH2O) Radicals

“…For example, at 600 K and 100 atm, the decomposition rate of Xu et al. is roughly four times smaller than that calculated in this work; at 1 Torr, the disagreement is an order of magnitude or more. Moreover, Xu et al.…”

“…Figure depicts ethoxy decomposition in helium at temperatures between 600 and 1000 K and compares the results of this work with those of Xu et al. , the only other study providing rate coefficients of ethoxy decomposition for variable pressures and temperatures above those in the study of Caralp et al. The agreement is clearly unsatisfactory, and the issue is further confounded by the fact that in both this work and the work of Xu et al., RRKM/ME results are in excellent agreement with the experimental data of Caralp et al.…”

“…Xu et al. have also performed RRKM/ME simulations for ethoxy in He and a number of other bath gases . Their simulation results compare favorably with the data of Caralp et al., although the data at 406 K are slightly underpredicted, whereas the data at 471 K are slightly overpredicted.…”

“…This phenomenon is elaborated upon below, and it occurs with the simplest α‐hydroxyalkyl radical as well, CH 2 OH → CH 3 O * → H+CH 2 O and has already been examined by Xu et al. in the case of CH 3 CHOH. Three other rate recommendations for α‐hydroxyethyl are worth mentioning.…”

“…For example, Xu et al. explored the C 2 H 5 O potential energy surface (PES) at the CCSD(T)/6–311+G(3df,2p) level of theory . Although the authors found new channels in addition to those considered by Caralp et al.…”