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

k_inf = 1.27E+16 T^(-0.63) exp(-383 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    2.0 
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). k_inf is 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.

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 Chang et al. (1994) 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 Chang et al. 1994), to the numbers listed at the top.

COMMENTS:

Served also as an optimization variable in the GRI-Mech 2.1 release. The rate coefficient was not changed from the GRI-Mech 1.2 value.

The pressure broadening is expressed in the Troe form.

Stewart et al. (1989)

Stewart, P.H., Smith, G.P., and Golden, D.M. (1989) Int. J. Chem. Kinet. 21, 923.

Cobos et al. (1990)

Cobos, C. J., and Troe, J. (1990) Z. Phys. Chem. 167, 129.

Chang et al. (1994)

Chang, E.J., Davidson, D.F., DiRosa, M.D., Hanson, R.K., and Bowman, C.T. (1994) 25th Symposium (International) on Combustion, Poster 23 in the Work-in-Progress Poster Session.

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    7.84E+13    2.36E-61    3.32E+74
     500       -32.0      -106.1    3.81E+13    3.81E-31    1.00E+44
    1000       -34.1      -107.6    3.61E+12    3.91E-09    9.22E+20
    1500       -34.3      -107.8    5.48E+11    2.80E-02    1.96E+13
    2000       -34.1      -107.3    1.29E+11    4.10E+01    3.15E+09
    2500       -33.6      -106.4    4.07E+10    2.25E+03    1.81E+07
    3000       -33.2      -105.0    1.56E+10    2.50E+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    1.47E+14    4.42E-61    3.32E+74
     500       -32.0      -106.1    9.71E+13    9.71E-31    1.00E+44
    1000       -34.1      -107.6    2.24E+13    2.43E-08    9.22E+20
    1500       -34.3      -107.8    4.48E+12    2.28E-01    1.96E+13
    2000       -34.1      -107.3    1.13E+12    3.60E+02    3.15E+09
    2500       -33.6      -106.4    3.69E+11    2.04E+04    1.81E+07
    3000       -33.2      -105.0    1.44E+11    2.30E+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    1.75E+14    5.28E-61    3.32E+74
     500       -32.0      -106.1    1.51E+14    1.51E-30    1.00E+44
    1000       -34.1      -107.6    6.12E+13    6.64E-08    9.22E+20
    1500       -34.3      -107.8    2.17E+13    1.11E+00    1.96E+13
    2000       -34.1      -107.3    7.65E+12    2.43E+03    3.15E+09
    2500       -33.6      -106.4    2.86E+12    1.58E+05    1.81E+07
    3000       -33.2      -105.0    1.20E+12    1.92E+06    6.26E+05
______________________________________________________________________