Calculation of anharmonic effect on the dissociation of ethylene glycol

Abstract

The unimolecular dissociation rate constants of ethylene glycol were examined using the MP2/6-311++G(d, p) method based on the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The effect of anharmonicity on the dissociation rate constants was evaluated at 500-4000 K temperatures of the canonical system and 25,182-50,235 cm(-1) total energies of the microcanonical system. The comparison of the results showed that the H2O elimination reaction played a critical role in the decomposition processes of ethylene glycol. The results of the rate constant calculations indicated that the H2O elimination reaction dominated at low temperatures, whereas the direct C-C bond dissociation reaction (CH2OHCH2OH -> CH2OH+CH2OH) dominated at high temperatures. For channel 1, CH2OH+CH2OH, the anharmonic effect of the canonical system was not observed, while it became more obvious with the increasing total energies in the microcanonical system. For channels 2-5, CH3CHO+H2O, CH2CHOH+H2O, CH3OH+CHOH, and CH2OHCHO+H-2, the anharmonic effect of canonical and microcanonical systems became more obvious with increasing temperatures and total energies. The comparison showed that, for channels 1 and 4, C-C bond dissociation and the anharmonic effect of the microcanonical system were more evident, whereas the anharmonic effect of the canonical system was more predominant for channels 2 (CH3CHO+H2O), 3 (CH2CHOH+H2O), and 5 (CH2OHCHO+H-2).