Approaches for Obtaining Accurate Rate Constants for Hydrogen Abstraction by a Chlorine Atom

被引:28
作者
Chan, Bun [1 ]
Radom, Leo
机构
[1] Univ Sydney, Sch Chem, Sydney, NSW 2006, Australia
基金
澳大利亚研究理事会;
关键词
CORRELATED MOLECULAR CALCULATIONS; AB-INITIO CALCULATIONS; GAS-PHASE REACTIONS; GAUSSIAN-BASIS SETS; THERMOCHEMICAL KINETICS; ATMOSPHERIC CHEMISTRY; DENSITY FUNCTIONALS; PHOTOCHEMICAL DATA; NONCOVALENT INTERACTIONS; CHEMICAL-REACTIONS;
D O I
10.1021/jp3007409
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
We have assessed computational methodologies for calculating the rate constants for hydrogen abstraction by Cl degrees for a selection of 12 reactions. For the conventional approach of calculating higher-level [B2K-PLYP/aug'-cc-pV[(T+d),(Q+d)]Z] single-point energies at lower-level [BH&H-LYP/6-31+G(d,p)] stationary points large deviations from experimental rate constants are found in a number of cases in which the activation energy is very low. These discrepancies are due largely to deviations in the calculated activation energies and can be further traced to the inability of the low level to adequately locate the transition structures. We have examined several alternative approaches for calculating rate constants, namely, IRCmax, IRCmax at 0 K (ZK-IRCmax, with zero-point vibration energies (ZPVEs) incorporated), variational transition-state theory (VTST), and VTST with the inclusion of an Eckart tunneling correction (VTST+E). We find that the low level gives reasonable values for the ZPVEs and thermal enthalpy and entropy corrections that are required in such approaches. While the VTST+E approach yields the closest agreement with experimental rate constants for the systems considered, we find that the simpler IRCmax approach gives adequate values and is able to avoid the major shortcomings of the conventional approach in a cost-effective manner.
引用
收藏
页码:3745 / 3752
页数:8
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