H + CH3 (+M) -> CH4 (+M)

k_o = 2.62E+33 T^(-4.76) exp(-2440 cal/mol /RT) cm^6/mol^2 s

k_inf = 1.393E+16 T^(-0.534) exp(-536 cal/mol /RT) cm3/mol s

F_cent = (1-0.783) exp(-T/74) + 0.783 exp(-T/2941) + exp(-6964/T)

Third-body efficiencies:
N2 1.0
H2 Enhanced by 2.0
H2O Enhanced by 6.0
CH4 Enhanced by 3.0
CO Enhanced by 1.5
CO2 Enhanced by 2.0
C2H6 Enhanced by 3.0
AR Enhanced by 0.7

SOURCE:

RRKM calculations for falloff, k_o, and F_cent from Stewart et al. (1989). For GRI-Mech 1.1, 1.2, and 2.11, k_inf was twice the Stewart et al. (1989) value in order to match the 700 K value of Cobos et al. (1990) while maintaining a slightly negative temperature dependence. The empirical k_inf expression for GRI-Mech 3.0, combined with a CH4 efficiency of 3.0, improves the fit to the decomposition rate constants of Chen et al.(75) and Barnes et al.(1989) near 1000K.

For the GRI-Mech 1.1 base mechanism, k_o and F_cent were from Stewart et al. (1989) using <delta E> = 0.30 kcal/mol. A multiplier to the rate coefficient was chosen to be an optimization variable for the optimization of GRI-Mech 1.1. As a result of that optimization, the rate coefficient was increased by a factor of 2.

For the GRI-Mech 1.2 optimization, new RRKM calculations were performed to provide revised values for k_o and F_cent as required to fit the data of Davidson et al. (1995) and as indicated from the results of the GRI-Mech 1.1 optimization. The GRI-Mech 1.2 computations used <delta-E> = 0.40 kcal/mol and an anharmonic treatment of the CH4 density of states. Anharmonicity constants were computed by the Birge-Sponer formula, D=w^2/(4wx). In the GRI-Mech 1.2 optimization, the preexponential factor of k_o was chosen to be an optimization variable, and as a result of optimization its value was increased by 1.4 (i.e., a factor of 1.4 higher than the data of Davidson et al. 1995).

COMMENTS:
Served also as an optimization variable in the GRI-Mech 3.0 release. The rate coefficient expressions were multiplied by 1.48 in the optimization.
The pressure broadening is expressed in the Troe form.

REFERENCES:

Stewart et al. (1989)
Stewart, P.H., Smith, G.P., and Golden, D.M. (1989) Int. J. Chem. Kinet. 21, 923.
Barnes et al.(1989)
Barnes, R.W., Pratt, G.L., and Wood, S.W. (1989) J. Chem. Soc. Farad. Trans. II 85, 229.
Brouard et al.(1989)
Brouard, M., MacPherson, M.T., and Pilling, M.J. (1989) J. Phys. Chem. 93, 4047.
Cobos et al. (1990)
Cobos, C. J., and Troe, J. (1990) Z. Phys. Chem. 167, 129.
Davidson et al. (1995)
Davidson, D.F., Hanson, R.K., and Bowman, C.T. (1995) Int. J. Chem. Kinet. 27, 303; Davidson, D.F., DiRosa, M.D., Chang, E.J., Hanson, R.K., and Bowman, C.T. (1992) 24th Symposium (International) on Combustion, p.599.
Hartig et al. (1971)
Hartig, R., Troe, J., and Wagner, H.Gg. (1971) 13th Symposium (International) on Combustion, p.147.
Kiefer et al. (1983)
Kiefer, J.H., Kapsalis, S.A., Al-Alami, M.Z., and Budach, K.A. (1983) Combust. Flame 51, 79.
Roth et al. (1979)
Roth, P., and Just, Th. (1979) Ber. Bunsenges. Phys. Chem. 83, 577.
Chen et al. (1975)
Chen, C.J., Back, M.H., and Back, R.A. (1975) Can. J. Chem. 53, 358. 

                        PRESSURE = 0.1 atm N2  
______________________________________________________________________
    Temp      delta-S     delta-H      kf          kr         Keq     
     (K)    (cal/mol K)  (kcal/mol) ----(mol,cm3,s)-----   (cm3/mol)  
______________________________________________________________________
                                                                      
     300       -29.3      -105.1    1.02E+14    3.06E-61    3.32E+74
     500       -32.0      -106.1    4.78E+13    4.78E-31    1.00E+44
    1000       -34.1      -107.6    4.03E+12    3.69E-09    9.22E+20
    1500       -34.3      -107.8    6.01E+11    3.06E-02    1.96E+13
    2000       -34.1      -107.3    1.41E+11    4.48E+01    3.15E+09
    2500       -33.6      -106.4    4.43E+10    2.44E+03    1.81E+07
    3000       -33.2      -105.0    1.70E+10    2.71E+04    6.26E+05
______________________________________________________________________


                        PRESSURE = 1 atm N2    
______________________________________________________________________
    Temp      delta-S     delta-H      kf          kr         Keq     
     (K)    (cal/mol K)  (kcal/mol) ----(mol,cm3,s)-----   (cm3/mol)  
______________________________________________________________________
                                                                      
     300       -29.3      -105.1    2.03E+14    6.08E-61    3.32E+74
     500       -32.0      -106.1    1.43E+14    1.43E-30    1.00E+44
    1000       -34.1      -107.6    2.92E+13    3.14E-08    9.22E+20
    1500       -34.3      -107.8    5.19E+12    2.65E-01    1.96E+13
    2000       -34.1      -107.3    1.42E+12    4.07E+02    3.15E+09
    2500       -33.6      -106.4    4.10E+11    2.26E+04    1.81E+07
    3000       -33.2      -105.0    1.58E+11    2.53E+05    6.26E+05
______________________________________________________________________


                        PRESSURE = 10 atm N2   
______________________________________________________________________
    Temp      delta-S     delta-H      kf          kr         Keq     
     (K)    (cal/mol K)  (kcal/mol) ----(mol,cm3,s)-----   (cm3/mol)  
______________________________________________________________________
                                                                      
     300       -29.3      -105.1    2.55E+14    7.67E-61    3.32E+74
     500       -32.0      -106.1    2.47E+14    2.47E-30    1.00E+44
    1000       -34.1      -107.6    9.66E+13    1.05E-07    9.22E+20
    1500       -34.3      -107.8    3.15E+13    1.61E+00    1.96E+13
    2000       -34.1      -107.3    9.74E+12    3.09E+03    3.15E+09
    2500       -33.6      -106.4    3.42E+12    1.89E+05    1.81E+07
    3000       -33.2      -105.0    1.39E+12    2.22E+06    6.26E+05
______________________________________________________________________

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