Reactions of methylene in the oxidation process of acetylene with oxygen atoms at 295 K

Abstract

Reactions of the methylene radical, formed in the oxidation process of acetylene with oxygen atoms at 295 K were studied in a fast flow reactor. Molecular beam sampling and mass spectrometric analysis allowed the monitoring of [CH2] as a function of reaction time. Applying the approach to steady-state analysis on the CH2 profile, the rate constant k2 for Reaction [2]: CH2+O→CO+2H was found to be (1.3±0.3)×10−10 molec−1 cm3 sec−1. In the presence of an excess amount of acetylene and molecular oxygen, the rate constants k3=(1.3±0.3)×10−12 molec−1 cm3 sec−1 of Reaction [3]: CH2+C2H2 →products and k4=(1.7±0.4)×10−12 molec−1 cm3 sec−1 of Reaction [4]: CH2+O2 →products were derived. Reaction [3] does not produce C3H4 in a direct step, but yields the radical C3H3 which then forms C3H4 in a further recombination reaction with hydrogen atoms. The rate constant of the reaction of C3H3 with oxygen atoms was found to be 4.7 times larger than that for hydrogen atoms. One of the products of Reaction [4] is the CHO radical and according to a proposed mechanism, the rate constant for its destruction by oxygen atoms is about 33 times larger than that for molecular oxygen.