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[Formula: see text]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[Formula: see text]K temperatures of the canonical system and 25,182–50,235[Formula: see text]cm[Formula: see text] 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 [Formula: see text] CH2OH[Formula: see text][Formula: see text][Formula: see text]CH2OH) dominated at high temperatures. For channel 1, CH2OH[Formula: see text][Formula: see text][Formula: see text]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[Formula: see text][Formula: see text][Formula: see text]H2O, CH2CHOH[Formula: see text][Formula: see text][Formula: see text]H2O, CH3OH[Formula: see text][Formula: see text][Formula: see text]CHOH, and CH2OHCHO[Formula: see text][Formula: see text][Formula: see text]H2, 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[Formula: see text][Formula: see text][Formula: see text]H2O), 3 (CH2CHOH[Formula: see text][Formula: see text][Formula: see text]H2O), and 5 (CH2OHCHO[Formula: see text][Formula: see text][Formula: see text]H2).