Properties of activation barriers from thermal rate data on forward and reverse reactions:  hydroxyl + hydrogen, amidogen + hydrogen, methyl + hydrogen and methyl + hydrogen chloride

Furue, Hiroshi; Pacey, Philip D.

doi:10.1021/j100367a041

Cited by 15 publications

(14 citation statements)

References 5 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Figure shows the minimum energy path, V MEP , the ground-state vibrationally adiabatic potential energy curve, V a G , and its zero-point energy, as a function of s . The barrier heights are 13.8 and 11.0 kcal mol -1 for the forward and reverse reactions, respectively, V a G ( f ) = 12.7 kcal mol -1 , and V a G ( r ) = 12.6 kcal mol -1 , and the heat of reaction at 0 K is −0.1 kcal mol -1 , in good agreement with the experimental value of JANAF, and in accordance with the recent experimental estimation of Furue and Pacey . The position of the maximum of the V a G curve practically coincides with the maximum of the V MEP , i.e., at s = 0.0.…”

Section: Resultssupporting

confidence: 89%

Recalibration of Two Earlier Potential Energy Surfaces for the CH₄ + H → CH₃ + H₂ Reaction. Application of Variational Transition-State Theory and Analysis of the Kinetic Isotope Effects Using Rectilinear and Curvilinear Coordinates

and

Corchado

1996

J. Phys. Chem.

View full text Add to dashboard Cite

We present a recalibration of the two most recent analytical potential energy surfaces for the CH4 + H → CH3 + H2 reaction. Assuming a correct functional form, the recalibration process allows one to update the original parameters in light of new experimental and theoretical data. As calibration criteria we use the reactant and product experimental properties, and the most recent ab initio saddle-point properties, which differ from the original values, especially the imaginary frequency. For both modified surfaces we use rectilinear and curvilinear coordinates to calculate the vibrational frequencies at nonstationary points. The rate coefficients are calculated with variational transition-state theory and, in general, agree with the experimental data in the temperature range 300−1500 K. They present only a slight dependence on the modified surfaces used but a major dependence on the choice of coordinate system, especially at low temperatures where the rectilinear coordinates yield rate coefficients practically double those of the curvilinear ones. We also provide a detailed analysis of the kinetic isotope effects (KIEs) for the reverse reactions. All KIEs are “normal”, i.e., the ratios of the unsubstituted/substituted rate coefficients are greater than unity and in good agreement with the experimental values. Both modified surfaces reproduce the experimental dependence of the KIEs on temperature, the agreement being best when curvilinear coordinates are used.

show abstract

Section: Resultssupporting

confidence: 89%

Recalibration of Two Earlier Potential Energy Surfaces for the CH₄ + H → CH₃ + H₂ Reaction. Application of Variational Transition-State Theory and Analysis of the Kinetic Isotope Effects Using Rectilinear and Curvilinear Coordinates

and

Corchado

1996

J. Phys. Chem.

View full text Add to dashboard Cite

show abstract

“…These results could be compared with those for reaction 17: 26 Parameters for this reaction, updated by including recent experimental results, are 58.5 ± 1.2 kJ mol -1 , 395 ± 36 K, and 806 ± 33 cm -1 , respectively. Reaction 3 is exoergic by 27 kJ mol -1 and would be expected to have a lower activation barrier than reaction 17, which is almost thermoneutral …”

Section: Discussionmentioning

confidence: 44%

“…The Arrhenius plot for reaction 3 in Figure is curved. Similar curvature has been observed previously in a number of reactions involving hydrogen transfer. , For several reactions it has been possible to fit a transition state theory model to the experimental data where κ( T / T *,V b ) is the tunneling factor, δ is the reaction path degeneracy, k B is Boltzmann's constant, T is the absolute temperature, h is Planck's constant, Q TS , Q A , and Q B are partition functions for the transition state (TS) and reactants (A and B), and V b is the effective barrier height including zero-point energy.…”

Section: Discussionmentioning

confidence: 99%

“…General features of the transition state theory method have been described elsewhere. Details specific to reaction 3 are given in the Appendix in the supporting information. − The three parameters V b , T *, and ω b , in eq 16 were fitted to the experimental data by nonlinear least squares . The parameters were found to be equal to 46.0 ± 1.0 kJ mol -1 , 375 ± 17 K, and 279 ± 8 cm -1 , respectively.…”

Section: Discussionmentioning

confidence: 99%

“…However, the more than 2-fold drop is surprising. In fact, the present value of ω b is the lowest we have found for any reaction …”

Section: Discussionmentioning

confidence: 99%

See 2 more Smart Citations

Initiation and Abstraction Reactions in the Pyrolysis of Acetone

Mousavipour

Pacey

1996

J. Phys. Chem.

Self Cite

View full text Add to dashboard Cite

The rates of the reactions, (CH3)2CO → CH3 + CH3CO (1) and CH3 + (CH3)2CO → CH4 + CH2COCH3 (3) have been studied in the flow pyrolysis of acetone at 825−940 K and 10−180 Torr. Yields of products were measured by gas chromatography. The rate constant, k 1, for the initiation reaction, determined from the sum of the yields of the termination products, was observed to be pressure dependent at 928 K. The Arrhenius expression for this reaction at the high-pressure limit (obtained from a nonlinear least-squares fit to the experimental data using the Troe factorization procedure) was found to be k 1 ∞ (s-1) = 1017.9±0.8 exp(−353 ± 14 kJ mol-1/RT). The Troe method has also been used to find the high-pressure limits of the cross-combination ratio for CH3 and CH3COCH2 radicals (1.9 ± 0.1) and of the quotient k 5/k 3 2, where reaction 5 is 2CH3 → C2H6. Calculated rate constants for reaction 3, when combined with values reported from photolysis experiments at lower temperatures, were found to exhibit a curved Arrhenius plot. A transition state theory model was fitted to the data for k 3 to determine the average transitional vibrational term value in the transition state (279 ± 8 cm-1), the effective activation barrier height (46 ± 1 kJ mol-1), and the full width of the barrier at half its height (52 ± 3 pm).

show abstract

The computation of the potential energy surface for H2 + OH ? H2O + H using ab initio and density functional theory methods

Jursic

1997

Int. J. Quant. Chem.

View full text Add to dashboard Cite

The reaction energy profile for H q OH ¬ H q H O was computed 2 2 using HF, MP2, MP4, QCISD, G1, G2, and G2MP2 ab initio methods. In addition, the Ž . B3LYP, B3P86, B3PW91, BLYP, BP291, and SVWN density functional theory DFT methods were also used. All the ab initio methods, with the exception of the G series, produced much higher activation barriers and heats of reaction than the experimental values. On the other hand, the DFT methods produced negative forward and reverse barriers which were too low, with the exception of the hybrid DFT methods. The G2 ab initio method generated energies which deviated from the experimental values by ; 1 kcalrmol and therefore should be considered a very accurate computational method. The hybrid DFT methods produced positive forward reaction barriers with energies that were 2᎐4 kcalrmol lower than the experimental values. The geometries of the transition state and energies computed by the ab initio and DFT methods were compared. These results suggest that, in the hybrid exchange functional, the portion of the Slater exchange term should be increased. This may be the reason why the computed energies were too low.

show abstract

Properties of activation barriers from thermal rate data on forward and reverse reactions: hydroxyl + hydrogen, amidogen + hydrogen, methyl + hydrogen and methyl + hydrogen chloride

Cited by 15 publications

References 5 publications

Recalibration of Two Earlier Potential Energy Surfaces for the CH₄ + H → CH₃ + H₂ Reaction. Application of Variational Transition-State Theory and Analysis of the Kinetic Isotope Effects Using Rectilinear and Curvilinear Coordinates

Recalibration of Two Earlier Potential Energy Surfaces for the CH₄ + H → CH₃ + H₂ Reaction. Application of Variational Transition-State Theory and Analysis of the Kinetic Isotope Effects Using Rectilinear and Curvilinear Coordinates

Initiation and Abstraction Reactions in the Pyrolysis of Acetone

The computation of the potential energy surface for H2 + OH ? H2O + H using ab initio and density functional theory methods

Contact Info

Product

Resources

About

Properties of activation barriers from thermal rate data on forward and reverse reactions: hydroxyl + hydrogen, amidogen + hydrogen, methyl + hydrogen and methyl + hydrogen chloride

Cited by 15 publications

References 5 publications

Recalibration of Two Earlier Potential Energy Surfaces for the CH4 + H → CH3 + H2 Reaction. Application of Variational Transition-State Theory and Analysis of the Kinetic Isotope Effects Using Rectilinear and Curvilinear Coordinates

Recalibration of Two Earlier Potential Energy Surfaces for the CH4 + H → CH3 + H2 Reaction. Application of Variational Transition-State Theory and Analysis of the Kinetic Isotope Effects Using Rectilinear and Curvilinear Coordinates

Initiation and Abstraction Reactions in the Pyrolysis of Acetone

The computation of the potential energy surface for H2 + OH ? H2O + H using ab initio and density functional theory methods

Contact Info

Product

Resources

About

Recalibration of Two Earlier Potential Energy Surfaces for the CH₄ + H → CH₃ + H₂ Reaction. Application of Variational Transition-State Theory and Analysis of the Kinetic Isotope Effects Using Rectilinear and Curvilinear Coordinates

Recalibration of Two Earlier Potential Energy Surfaces for the CH₄ + H → CH₃ + H₂ Reaction. Application of Variational Transition-State Theory and Analysis of the Kinetic Isotope Effects Using Rectilinear and Curvilinear Coordinates