Rate Coefficients of the Cl + CH3C(O)OCH3 鈫?HCl + CH3C(O)OCH2 Reaction at Different Temperatures Calculated by Transition-State Theory with ab Initio and De

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• 作者：Ronald Chow ; Maggie Ng ; Daniel K. W. Mok ; Edmond P. F. Lee ; John M. Dyke
• 刊名：Journal of Physical Chemistry A
• 出版年：2014
• 出版时间：March 20, 2014
• 年：2014
• 卷：118
• 期：11
• 页码：2040-2055
• 全文大小：711K
• 年卷期：v.118,no.11(March 20, 2014)
• ISSN：1520-5215

文摘

The complex relationship of computed rate coefficients (k鈥檚) with different ab initio/DFT and TST levels was studied. The MEPs, gradients, and Hessians of the title reaction were computed using the MP2 and DFT methods. Electronic energies were improved to the UCCSD(T)-F12x/CBS level, and k鈥檚 were calculated at the TST, CVT, and ICVT levels with various tunnelling corrections. Although computed microcanonical and tunnelling effects are small, computed kp>TSTp> values are larger than computed kp>TST/ZCTp> and kp>TST/SCTp> values by 3 orders of magnitude at low temperatures, because computed 魏p>(TST/CAG)p> values are as small as 6 脳 10p>鈥?p>. In some cases, the maximum of the 螖G/s curves at a certain T is far away from the MEP maximum. This raises the question of the range of s to be considered in a VTST calculation and, of a possible scenario, where no maximum on the 螖G curve can be located and hence a breakdown of VTST occurs. For dual-level direct dynamics calculations, different entropic contributions from different lower levels can lead to computed k鈥檚, which differ by more than 1 order of magnitude. Matching computed and experimental k values leads to an empirical barrier of 1.34 kcal molp>鈥?p> for the title reaction.