Concerted non-least-motion pathway for the singlet methylene insertion reaction CH2(1A1) + H2 .fwdarw. CH4

Bauschlicher, Charles W.; Haber, Kenneth S.; Schaefer, Henry F.; Bender, Charles F.

doi:10.1021/ja00453a014

Cited by 64 publications

(28 citation statements)

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“…Schaefer and co-workers have estimated the barrier for reaction 11 to be between 42 and 63 kJ mol -1 , while for the corresponding insertion into singlet methylene a Woodward-Hoffmann barrier of 113 kJ mol -1 is predicted, and the concerted, twostep insertion into singlet-methylene is expected to occur without barrier. 55 Figure 9d is very similar to Figure 3 of ref 56, in which the singlet diabatic version of the potential surface for the hydrogen elimination is shown.…”

Section: Potential Surfaces For the H 2 Elimination And Absupporting

confidence: 70%

Global Analytical Potential Hypersurface for Large Amplitude Nuclear Motion and Reactions in Methane II. Characteristic Properties of the Potential and Comparison to Other Potentials and Experimental Information

Marquardt

Qüack

2004

J. Phys. Chem. A

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The global analytical potential surface for the electronic ground state of methane developed in paper I is analyzed and discussed in detail. A new determination of the experimental potential surface for the CH chromophore in CHD 3 , obtained from more recently measured line positions and integrated absorption coefficients, is also reported. The complete, nine-dimensional calculation of the vibrational ground state by diffusion quantum Monte Carlo on the fully anharmonic potential surface allows the determination of r e ) (1.086 ( 0.002) Å with a high level of certainty from comparison with experimental values of rotational constants for methane and isotopomers. Other results regarding properties of the anharmonic potential surface close to the equilibrium configuration are theoretical values for the vibrationally induced electric dipole moments in CH 3 D, CH 2 D 2 , and CHD 3 , which are obtained in conjunction with a nine-dimensional, vector-valued representation of the electric dipole moment in this molecule and agree well with the experimental data. It is shown that, if equilibrium geometry and harmonic force field are fixed to experimental values, the overtone spectrum of the CH chromophore in CHD 3 can be described in an acceptable way (〈|ν cal -ν obs |〉 ≈ 40 cm -1 up to 18 000 cm -1 (METPOT 3). The agreement can be improved to within 17 cm -1 (METPOT 4), on the average, if the anharmonic part of the model potential is refined with data from the experimentally derived, three-dimensional CH chromophore potential surface from Lewerenz and Quack (J. Chem. Phys. 88). For this purpose, the analytical representation of the potential, mainly along the bending degrees of freedom, must be sufficiently flexible, as shown by the present calculations. The accuracy regarding the description of spectroscopic data pertaining to highly excited vibrational states and the global character of the proposed potential surface representation render it a powerful instrument for the theoretical treatment of chemical reaction dynamics. A relation to reaction kinetics can be established through calculation of the lowest adiabatic channel on the complete nine-dimensional potential hypersurface for methane using quasiadiabatic channel quantum Monte Carlo techniques. It is found that the behavior of this channel, corresponding approximately to an exponential interpolation with a parameter R ≈ 0.7-0.8 Å -1 in the adiabatic channel model, is consistent with empirical results obtained from experiment. Further refinements of the models are feasible and expected, when full dimensional calculations of the solution of the rovibrational Schrödinger equation will be performed.

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Section: Potential Surfaces For the H 2 Elimination And Absupporting

confidence: 70%

Global Analytical Potential Hypersurface for Large Amplitude Nuclear Motion and Reactions in Methane II. Characteristic Properties of the Potential and Comparison to Other Potentials and Experimental Information

Marquardt

Qüack

2004

J. Phys. Chem. A

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“…However, the identity of X plays an role in the height of the activation barrier since the CH 2 group is a carbenoid and not a free carbene, which inserts into H 2 without an energy barrier. 30 The values of the activation energy become progressively higher as X changes from F to OMe and to NMe 2 . The calculated structures of Ce(η 2 -CH 2 X) when X is a halide are very similar to those for X = F. 1 Descending the halide series results in longer C-Xbondsand an increase in the Ce-C-X angle that varies from 71° for F to 86° for I.…”

Section: Computational Studiesmentioning

confidence: 97%

Hydrogen for X-Group Exchange in CH₃X (X = Cl, Br, I, OMe, and NMe₂) by Monomeric [1,2,4-(Me₃C)₃C₅H₂]₂CeH: Experimental and Computational Support for a Carbenoid Mechanism

et al. 2009

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“…1 CH 2 reactions tend to occur via insertion mechanisms with zero or negative activation energies 12 in contrast to reactions of the triplet ground state, which generally have significant and positive activation energies.…”

Section: Introductionmentioning

confidence: 99%

Kinetics and Product Branching Ratios of the Reaction of ¹CH₂ with H₂ and D₂

Gannon¹,

Blitz²,

Pilling³

et al. 2008

J. Phys. Chem. A

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The reactions of singlet methylene (a(1)A1 (1)CH2) with hydrogen and deuterium have been studied by experimental and theoretical techniques. The rate coefficients for the removal of singlet methylene with H2 (k1) and D2 (k2) have been measured from 195 to 798 K and are essentially temperature-independent with values of k1 = (10.48 +/- 0.32) x 10(-11) cm(3) molecule(-1) s(-1) and k2 = (5.98 +/- 0.34) x 10(-11) cm(3) molecule(-1) s(-1), where the errors represent 2sigma, giving a ratio of k1/k2 = 1.75 +/- 0.11. In the reaction with H2, singlet methylene can be removed by reaction giving CH3 + H or deactivated to ground-state triplet methylene. Direct measurement of the H atom product showed that the fraction of relaxation decreased from 0.3 at 195 K to essentially zero at 398 K. For the reaction with deuterium, either H or D may be eliminated. Experimentally, the H:D ratio was determined to be 1.8 +/- 0.5 over the range 195-398 K. Theoretically, the reaction kinetics has been predicted with variable reaction coordinate transition state theory and with rigid-body trajectory simulations employing various high-level, ab initio-determined potential energy surfaces. The magnitudes of the calculated rate coefficients are in agreement with experiment, but the calculations show a significant negative temperature dependence that is not observed in the experimental results. The calculated and experimental H to D ratios from the reaction of singlet methylene with D2 are in good agreement, suggesting that the reaction proceeds entirely through the formation of a long-lived methane intermediate with a statistical distribution of energy.

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Concerted non-least-motion pathway for the singlet methylene insertion reaction CH2(1A1) + H2 .fwdarw. CH4

Cited by 64 publications

References 0 publications

Global Analytical Potential Hypersurface for Large Amplitude Nuclear Motion and Reactions in Methane II. Characteristic Properties of the Potential and Comparison to Other Potentials and Experimental Information

Global Analytical Potential Hypersurface for Large Amplitude Nuclear Motion and Reactions in Methane II. Characteristic Properties of the Potential and Comparison to Other Potentials and Experimental Information

Hydrogen for X-Group Exchange in CH₃X (X = Cl, Br, I, OMe, and NMe₂) by Monomeric [1,2,4-(Me₃C)₃C₅H₂]₂CeH: Experimental and Computational Support for a Carbenoid Mechanism

Kinetics and Product Branching Ratios of the Reaction of ¹CH₂ with H₂ and D₂

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Concerted non-least-motion pathway for the singlet methylene insertion reaction CH2(1A1) + H2 .fwdarw. CH4

Cited by 64 publications

References 0 publications

Global Analytical Potential Hypersurface for Large Amplitude Nuclear Motion and Reactions in Methane II. Characteristic Properties of the Potential and Comparison to Other Potentials and Experimental Information

Global Analytical Potential Hypersurface for Large Amplitude Nuclear Motion and Reactions in Methane II. Characteristic Properties of the Potential and Comparison to Other Potentials and Experimental Information

Hydrogen for X-Group Exchange in CH3X (X = Cl, Br, I, OMe, and NMe2) by Monomeric [1,2,4-(Me3C)3C5H2]2CeH: Experimental and Computational Support for a Carbenoid Mechanism

Kinetics and Product Branching Ratios of the Reaction of 1CH2 with H2 and D2

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Hydrogen for X-Group Exchange in CH₃X (X = Cl, Br, I, OMe, and NMe₂) by Monomeric [1,2,4-(Me₃C)₃C₅H₂]₂CeH: Experimental and Computational Support for a Carbenoid Mechanism

Kinetics and Product Branching Ratios of the Reaction of ¹CH₂ with H₂ and D₂