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Development of Microcanonical Statistical Rate Theory for Unimolecular Reactions
Published in Takayuki Fueno, The Transition State, 2019
where BRC is the rotational constant of the dissociating molecule. This potential, plotted against the one-dimensional reaction coordinate, has a broad barrier and hence the transition state based on the maximum energy criteria can be defined at rRC = r+. As J varies, however, the location of the transition state changes. In terms of variational transition state theory, the location of the transition state also depends both on the available energy and on the state sum of the vibrations orthogonal to the reaction coordinate. Thus the unique location cannot be defined for such a loose transition state and consequently the way of estimating the state sum as a function of the reaction coordinate significantly affects the value of the dissociation rate.
Theoretical study on the reaction of nitric oxide with 2-hydroxyethyl radical
Published in Molecular Physics, 2021
Xiaowen Wang, Jinou Song, Zhongwei Meng, Gang Lv, Xiangrong Li, Han Wu
Figure S3 (Supplementary Material) depicts the calculation of kRw1 (the rate coefficient of the reaction of Rw1 to form IM1 as shown in Scheme 1). It is carried out using the canonical variational transition state theory (CVT). In CVT, the barrierless entrance pathway forming IM1 is scanned at B3LYP/6-311++G(d, p) level of theory to obtain the minimum energy path (MEP), then the MEP energies were refined at CCSD(T)/cc-pVTZ level (Figure S2, Supplementary Material). Since there is no unpaired electron in the ON – CH2CH2OH structure, the NO – CH2CH2OH scan was carried out in a restricted calculation. Some selected points along MEP are submitted to rate coefficients calculations and the minimum value is chosen as the CVT rate coefficient, while the corresponding point structure is used as variational transition state. As shown in Figure S3 (Supplementary Material), the TST rate coefficient curve of Rw1 is performed by CCSD(T) // B3LYP method at 298 K and 1.0 bar. The minimum rate coefficient (i.e. kRw1, CVT= 3.95 × 10−11 cm3 molecule−1 s−1) is obtained at the point with the distance of 3.45 Å between C and N atom, and this point is exactly the peak of CCSD(T) // B3LYP level in Figure S2.
Mechanistic studies and rate coefficients calculations of hydrogen abstraction from ethanol by methyl peroxy radical and hydroperoxyl radical
Published in Molecular Physics, 2020
Gai Shi, Jinou Song, Fei Cao, Gang Lv, Zhijun Li
The electronic structure calculations were performed using Gaussian 09 program package [25]. The geometries of the stationary points were optimised at the MP2/aug-cc-pVTZ level of theory [26] and the energetics were refined at the CCSD(T)/aug-cc-pVTZ and the QCISD(T)/cc-pVTZ levels of theory [27,28]. Harmonic vibrational frequencies were calculated to confirm the nature of the stationary points and the zero-point energy (ZPE) was obtained. Intrinsic reaction coordinate (IRC) calculations [29,30] were performed to show all of transition states connecting to the exact reactants and products. The minimum energy path (MEP) was obtained by CCSD (T) method based on the reaction coordinates with a gradient step size of 0.02 (amu)1/2 Bohr. The basis set superposition error (BSSE) was performed and the single-point energies of all of the stationary points were tested [31]. The rate coefficients of all of the channels were computed at the canonical variational transition state theory (VTST) and the conventional transition state theory (TST) with the Eckart tunneling (Eck) correction using the kISThelp2014 program [32].
Reaction probability and defluorination mechanisms of a potent greenhouse gas SF5CF3 attacked by CH3 radical: a theoretical study
Published in Molecular Physics, 2018
Yan Liu, Yue-tian Huang, Wen-liang Wang
The reaction rate constant were calculated with the variational transition state theory (VTST) [26,27], which is designed to vary the dividing surface along MEP to minimise the rate and to minimise the error of the recrossing trajectories. For a canonical ensemble at a given temperature T, the canonical variational transition state theory (CVT) [28] rate constant is given by , in which where is the generalised transition state theory rate constants, is the internal partition function of the generalised transition state, is the reactant partition function. , and h are the symmetry factor, , Boltzmann’s constant and the Planck’s constant, respectively.