Mixed Quantum-Classical Reaction Path Dynamics of C₂H₅F → C₂H₄ + HF

Abstract

A mixed quantum-classical method for calculating product energy partitioning based on a reaction path Hamiltonian is presented and applied to HF elimination from fluoroethane. The goal is to describe the effect of the potential energy release on the product energies using a simple model of quantized transverse vibrational modes coupled to a classical reaction path via the path curvature. Calculations of the minimum energy path were done at the B3LYP/6-311++G(2d,2p) and MP2/6-311++G** levels of theory, followed by energy-partitioning dynamics calculations. The results for the final HF vibrational state distribution were found to be in good qualitative agreement with both experimental studies and quasiclassical trajectory simulations.

The Unimolecular Reactions of CF3CHF2 Studied by Chemical Activation: Assignment of Rate Constants and Threshold Energies to the 1,2-H Atom Transfer, 1,1-HF and 1,2-HF Elimination Reactions, and the Dependence of Threshold Energies on the Number of F-Atom Substituents in the Fluoroethane Molecules

“…The structure of the transition states for 1,2-HF elimination given by several levels of electronic-structure calculations are very similar, and the transition-state structures seem to satisfy the majority of the experimental data, including kinetic-isotope effects , and energy disposal. − One notable feature is the more nearly planar geometry around the carbon atom attached to the leaving F atom, and this is clearly the case for C 2 F 5 H shown in Figure . In fact, for the C 2 H 5 F reaction, relaxation of the CH 2 group associated with the leaving H atom is responsible for a significant part of the vibrational energy acquired by C 2 H 4 . , The influence of the mass of the atoms attached to the carbon atoms on the energy disposal is still the subject of research, but the 128.4° and 170.2° out-of-plane CF 2 angles suggest that C 2 F 4 also would acquire vibrational energy as it become planar; see Figure .…”

“…The experimental threshold energies for HF elimination from the fluoroethane series of molecules are compared with the calculated results from two commonly used methods, M06-2X and B3PW91, in Table to illustrate trends, rather than attempt to obtain the best agreement between experimental and calculated threshold energies. The identification of computational methods to obtain reliable threshold energies also is relevant for selection of methods that are suitable for direct-dynamic treatments − of the exit channel. Thermal- and chemical-activation studies are in agreement for the threshold energy assignments for the first four members of the series.…”

“…In fact, for the C 2 H 5 F reaction, relaxation of the CH 2 group associated with the leaving H atom is responsible for a significant part of the vibrational energy acquired by C 2 H 4 . 46,47 The influence of the mass of the atoms attached to the carbon atoms on the energy disposal is still the subject of research, 45 but the 128.4°and 170.2°out-of-plane CF 2 angles suggest that C 2 F 4 also would acquire vibrational energy as it become planar; see Figure 2. The transition states and the results of IRC calculations for 1,1-HF elimination and 1,2-H atom transfer are more unusual, and they can be fruitfully discussed.…”

Dissociative Chemisorption of Methane on Ni and Pt Surfaces: Mode-Specific Chemistry and the Effects of Lattice Motion

“…The RPH has had many applications, particularly to transition state theory calculations of rate constants involving polyatomic molecules . It has also been used in several dynamical studies, − often involving semiclassical or mixed quantum-classical approximations. To our knowledge, this is the first attempt to use the RPH to implement a fully quantum reactive scattering calculation involving a polyatomic molecule.…”

Mixed Quantum-Classical Reaction Path Dynamics of HCl Elimination from Chloroethane

“…Stationary points were optimized using the default algorithms in NWChem. Due to its success and efficiency in describing the dynamics of HF elimination from C 2 H 5 F, the B3LYP hybrid DFT exchange−correlation functional with the 6-311++G(2d,2p) basis set was used for the electronic structure calculations. The “xfine” numerical grid integration directive in NWChem was used to improve the accuracy of all B3LYP calculations, which uses 100 radial and 1202 angular points for H, 100 radial and 1454 angular points for C, and 125 radial and 1454 angular points for Cl …”