Department of Chemistry, College of Environmental Science and Forestry, State University of New York, Syracuse, NY 13210, USA.
Phys Chem Chem Phys. 2011 Oct 28;13(40):17969-77. doi: 10.1039/c1cp21691k. Epub 2011 Aug 11.
The kinetics of three unimolecular reactions of the n-propylperoxy radical were studied by canonical variational transition state theory and multidimensional small curvature tunneling (SCT). The reactions studied were 1,5 and 1,4 H-migration, and HO(2) elimination. Benchmark calculations were carried out at the CCSD(T) level in order to determine which density functional to use for SCT calculations for each reaction. For 1,5 and 1,4 H-migration, and HO(2) elimination, the M05-2X, B3LYP and B1B95 functionals, respectively, performed closest to the benchmark when coupled to the 6-311+G(2df,2p) basis set. The SCT tunneling corrections, κ(T), computed here were much larger than those calculated from the Wigner or zero-curvature tunneling treatments at low temperatures, but the asymmetric Eckart method works surprisingly well in these three reactions. Comparison of energy-dependent transmission coefficients, Γ(E), indicates that not only the magnitude, but also the sign, of the error in the Eckart approximation is a function of energy; therefore, the error introduced by using the Eckart approach depends strongly on the steady state energy distribution. These results may provide guidance for future studies of tunneling effects in reactions of other peroxy radicals.
通过正则变分过渡态理论和多维小曲率隧道（SCT）研究了正丙基过氧自由基的三个单分子反应的动力学。研究的反应是 1,5 和 1,4 H-迁移以及 HO(2)消除。为了确定每种反应的 SCT 计算应使用哪种密度泛函，进行了 CCSD(T) 水平的基准计算。对于 1,5 和 1,4 H-迁移以及 HO(2)消除，当与 6-311+G(2df,2p)基组结合时，M05-2X、B3LYP 和 B1B95 泛函分别最接近基准。此处计算的 SCT 隧道校正κ(T)在低温下远大于从 Wigner 或零曲率隧道处理计算的值，但不对称 Eckart 方法在这三个反应中出人意料地有效。能量相关传输系数Γ(E)的比较表明，Eckart 近似的误差不仅大小，而且符号，都是能量的函数；因此，使用 Eckart 方法引入的误差强烈依赖于稳态能量分布。这些结果可能为未来研究其他过氧自由基反应中的隧道效应提供指导。
