High-temperature reactions of triplet methylene and ketene with radicals

Abstract

The reactions of CH/sub 2/ and ketene with CH/sub 2/ and H have been investigated at elevated temperatures in the postshock region behind reflected shocks. Atomic (ARAS) and molecular resonance absorption spectrometry was used to record simultaneously H-atom and CO-molecule concentration profiles. The thermal decomposition of very low initial concentrations of ketene (2-50 ppm CH/sub 2/CO/Ar) served as a source for methylene. The experiments were conducted in the temperature range of 1650-2800 K at total densities of 5 x 10/sup -6/ to 1.3 x 10/sup -5/ mol cm/sup -3/. For temperatures above 2000 K the following rate coefficients (k in cm/sup 3/ mol/sup -1/ s/sup -1/) were deduced: CH/sub 2/ + CH/sub 2/ = C/sub 2/H/sub 2/ + 2H, k = (10 +/- 2) x 10/sup 13/; CH/sub 2/ + H = CH + H/sub 2/, k = (8 +/- 2) x 10/sup 12/. For temperatures between 1650 and 1850 K a value of (1.8 +/- 0.6) x 10/sup 13/ is deduced for the reaction of ketene with H atoms. 30 references, 9 figures, 1 table.