Semiclassical Transition State Theory (SCTST) Rate\nCoefficients for the Unimolecular Decomposition of the Ethoxy (CH<sub>3</sub>CH<sub>2</sub>O) Radical

The\nthermal unimolecular decay of ethoxy is important in high-temperature\ncombustion environments where the ethoxy radical is a key reactive\nintermediate. Two dissociation pathways of ethoxy, including the β-C–C\nscission to yield CH<sub>3</sub> + CH<sub>2</sub>O and the H-elimination\nto make H + CH<sub>3</sub>CHO, were characterized using a high-level\ncoupled-cluster-based composite quantum chemical method (mHEAT-345(Q<sub>Λ</sub>)). The former route is found to be dominant while the\nlatter is insignificant, in agreement with previous experimental and\ntheoretical studies. Thermal rate coefficients are calculated for <i>P</i> = 0.001–658 atm (of air) and <i>T</i> = 300–2500 K using semiclassical transition state theory\n(SCTST) in combination with a pragmatic two-dimensional <i>E</i>,<i>J</i>-resolved master equation (2DME). The effects\nof tunneling and anharmonicity on the calculated rate constants are\nalso examined. The tunneling factor is found to be inversely dependent\non pressure, contrary to previous observations of pressure-dependent\ntunneling in entrance channels.