标题：Barrierless association of CF2 and dissociation of C2F4 by variational transition-state theory and system-specific quantum Rice–Ramsperger–Kassel theory
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2016
卷号：113
期号：48
页码：13606-13611
DOI：10.1073/pnas.1616208113
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceBarrierless association reactions and bond dissociation reactions play important roles in combustion and atmospheric chemistry, and calculating their rate constants is challenging for both electronic structure theory and kinetics theory. Here, we validate an exchange-correlation functional against high-level electronic structure theory, and we use the resulting density functional method for direct dynamics calculations of the pressure-dependent rate constants for the C=C bond dissociation of C2F4 by applying multifaceted variable-reaction-coordinate variational transition-state theory with the recently developed system-specific quantum Rice-Ramsperger-Kassel theory. This work presents a prototypical example of the full treatment of the kinetics of barrierless reactions and their reverse reactions, including variational optimization of the transition state, multidimensional tunneling, and pressure effects. Bond dissociation is a fundamental chemical reaction, and the first principles modeling of the kinetics of dissociation reactions with a monotonically increasing potential energy along the dissociation coordinate presents a challenge not only for modern electronic structure methods but also for kinetics theory. In this work, we use multifaceted variable-reaction-coordinate variational transition-state theory (VRC-VTST) to compute the high-pressure limit dissociation rate constant of tetrafluoroethylene (C2F4), in which the potential energies are computed by direct dynamics with the M08-HX exchange correlation functional. To treat the pressure dependence of the unimolecular rate constants, we use the recently developed system-specific quantum Rice-Ramsperger-Kassel theory. The calculations are carried out by direct dynamics using an exchange correlation functional validated against calculations that go beyond coupled-cluster theory with single, double, and triple excitations. Our computed dissociation rate constants agree well with the recent experimental measurements.
关键词：bond dissociation ; barrierless reaction ; variable-reaction-coordinate variational transition-state theory ; falloff ; system-specific quantum RRK theory
