A Method of Calculating Tunneling Corrections for Eckart Potential Barriers

Eyringpy is a modular program for calculating thermochemical properties and rate constants for reactions in the gas phase and in solution. The code is written in Python and it has a user‐friendly interface and a simple input format. Unimolecular and bimolecular reactions with one and two products are supported. Thermochemical properties are estimated through canonical ensemble and rate constants are computed according to the transition state theory. One‐dimensional Wigner and Eckart tunneling corrections are also available. Rate constants of bimolecular reactions involving the formation of pre‐reactive complexes are also estimated. To compute rate constants in solution, Eyringpy uses the Collins–Kimball theory to include the diffusion‐limit, the Marcus theory for electron transfer processes, and the molar fractions to account for the solvent pH effect.

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“…The parameters a 1 , a 2 , and d are calculated directly from the relationships proposed by Johnston and Heicklen, and Brown that are expressed as

a_{i} = {[2 (ɛ + υ_{i}) / π u^{*}]}^{\frac{1}{2}} {(α_{1}^{- 1 / 2} + α_{2}^{- 1 / 2})}^{- 1}, i = 1, 2

d = {(2 π)}^{- 1} {((||, 4 α_{1} α_{2} - π^{2}))}^{\frac{1}{2}},

α_{i} = 2 π Δ H_{f}^{‡, 0 normalK} / h ν^{‡}, i = 1, 2; j = f, r

υ_{i} = Δ H_{f}^{‡, 0 normalK} / k_{B} italicT, i = 1, 2; j = f, r

ɛ = ((), E - Δ H_{f}^{‡, 0 normalK}) / k_{B} italicT

u^{*} = h ν^{‡} / k_{B} italicT,

where

Δ H_{f}^{‡, 0 n...}

…”

Section: Tunneling Correctionsmentioning

confidence: 99%

Eyringpy: A program for computing rate constants in the gas phase and in solution

Dzib¹,

Cabellos

Ortíz‐Chi

et al. 2018

Int J of Quantum Chemistry

154

168

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“…We estimated contribution of QMT to the observed KIE using UM06-2X PES 33 and asymmetric Eckart barrier for 1,5-HAT step from 1a to 1a -C1; 34 the computed ratios of tunneling correction factors (Γ* H /Γ* D ) for 1a and its D 2 -isotopomer are 399 and 34 at 232.5 and 298 K (Table 2). If the corresponding over-the-barrier KIEs at 232.5 and 298 K are near their typical values of 8 and 5, 10c,11 then estimated k H / k D ≈ 3200 and 170 (Table S14, SI) are not far off from the experimental values k H / k D of 1380 and 156 (Table S11 and Figure S2, SI).…”

mentioning

confidence: 99%

Intramolecular Hydrogen Atom Transfer in Aminyl Radical at Room Temperature with Large Kinetic Isotope Effect

et al. 2017

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We report a large kinetic isotope effect at 298 K, kH/kD ≈ 150, associated with an intramolecular 1,5-hydrogen atom transfer (1,5-HAT) in the decay of PEGylated carbazyl (aminyl) radical in solution. The experimental observations surprisingly combine the hallmarks of tunneling, including large KIEs and unusual activation parameters, with linear Arrhenius and Eyring plots over an exceptionally wide temperature range of 116 K.

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“…Out of the three decomposition channels considered, Helimination (reaction channel 2) is susceptible to strong tunnelling effect. Tunnelling calculations considering an Eckart-type barrier have been taken into account and the calculation was performed using the procedure proposed by Brown [29], which included the forward and reverse energy barriers for the reaction path that follows.…”

Section: Methodsmentioning

confidence: 99%

“…E, k B and h are the barrier height including zero-point energy (ZPE), Boltzmann's and Planck's constants, respectively. Calculation for the tunnelling correction factor (T) was made using the Eckart potential as implemented by Brown [29] that incorporated the forward and reverse energy barriers. The tunnelling correction for H-atom elimination (channel 2) was found to be 3.813 compared with 2.170 calculated by simple Wigner's method [33].…”

Section: Rate Constantmentioning

confidence: 99%

Computational studies on the thermal decomposition of the CH₂FOCHFO radical

2013

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Theoretical studies have been carried out on the kinetics and thermochemistry of the thermal decomposition of the CH 2 FOCHFO radical formed during the photo-oxidation of CH 2 FOCH 2 F (HFE-152E) using the dual-level method of obtaining the optimised structure at DFT(M06-2X)/6-311 + + G(d,p) followed by a single-point energy calculation at the G3 level of theory. The rate constant for different reaction channels involved during the decomposition processes of CH 2 FOCHFO is evaluated at 298 K and 1 atm using canonical transition-state theory. The results point out that the C-H bond scission is the dominant path involving an energy barrier of 9.5 kcal mol −1 determined at the G3 level of theory. A potential energy diagram is constructed and the results are compared with the data available from the literature for a structurally similar molecule.

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A Method of Calculating Tunneling Corrections for Eckart Potential Barriers

Abstract: A method is presented for the direct calculation of tunneling corrections for unsymmetrical Eckart type potential barriers. It is based on a modified 6-point Gaussian quadrature formula. Accuracy is better than 1 percent over a wide range of tunneling parameter values.

Cited by 88 publications

References 7 publications

Eyringpy: A program for computing rate constants in the gas phase and in solution

Eyringpy: A program for computing rate constants in the gas phase and in solution

Intramolecular Hydrogen Atom Transfer in Aminyl Radical at Room Temperature with Large Kinetic Isotope Effect

Computational studies on the thermal decomposition of the CH₂FOCHFO radical

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A Method of Calculating Tunneling Corrections for Eckart Potential Barriers

Abstract: A method is presented for the direct calculation of tunneling corrections for unsymmetrical Eckart type potential barriers. It is based on a modified 6-point Gaussian quadrature formula. Accuracy is better than 1 percent over a wide range of tunneling parameter values.

Cited by 88 publications

References 7 publications

Eyringpy: A program for computing rate constants in the gas phase and in solution

Eyringpy: A program for computing rate constants in the gas phase and in solution

Intramolecular Hydrogen Atom Transfer in Aminyl Radical at Room Temperature with Large Kinetic Isotope Effect

Computational studies on the thermal decomposition of the CH2FOCHFO radical

Contact Info

Product

Resources

About

Computational studies on the thermal decomposition of the CH₂FOCHFO radical