Kinetic Investigation of the + H -> CH(X2II) + H2 Reaction in the Temperature Range 400 K < T < 1000 K

Article abstract of DOI:10.1021/j100046a022

The <*> + H -> CH(X²II) + H2 reaction (1) was investigated in CH2CO/O systems (T = 400, 500, 650, and 950 K, p = 2 Torr) as well as in C2H2/O systems (T=590 and 890 K, p = 4 Torr) using discharge-flow/molecular beam sampling mass spectrometry techniques (D-F/MBMS).The first rate coefficient data at temperatures intermediate between room and flame temperature are presented.The <*> + H rate constant was measured relative to the well-known <*> + O = (1.3 +/- 0.3) x 1E-10 cm³ molecule^-1 s^-1 from the change of the quasi-steady state CH2 concentration upon varying the / ratio at given CH2 formation rate.In the temperature range of interest, the k¹ coefficient was found to exhibit a clear-cut negative temperature dependence.The following k₁ was obtained: (i) using the CH2CO + O reaction as CH2 source, (2.93 +/- 0.80) x 1E-10 at 400 K, (2.05 +/- 0.57) x 1E-10 at 500 K, (1.22 +/- 0.31) x 1E-10 at 650 K, and (1.18 +/- 0.32) x 1E-10 at 950 K; (ii) using the C2H2 + O system as CH2 source, (1.90 +/- 0.58) x 1E-10 at 590 K and (1.12 +/- 0.36) x 1E-10 at 890 K (k in cm³ molecule^-1 s^-1; 95percent cofidence intervals, including possible systematic errors).The data obtained with the two CH2 sources are in good mutual agreement.The decrease of k₁ with temperature is in accord with literature k₁ data at room temperature on one side and in the 1500-2500 K range on the other.However, the observed temperature dependence in the 300-1000 K range is much less steep than predicted by the recommended k₁(T) expression in a recent evaluation.An equation that fits all available data reasonably well is k₁ = 3.8 x 1E-10 exp<-1.3 x 1E-3 T (K)> cm³ molecule^-1 s^-1, for T = 300-2500 K.