Observation of a new channel, the production of CH, in the abstraction reaction of OH radicals with acetaldehyde.

Using laser flash photolysis coupled to photo-ionization time-of-flight mass spectrometry (PIMS), methyl radicals (CH) have been detected as primary products from the reaction of OH radicals with acetaldehyde (ethanal, CHCHO) with a yield of ∼15% at 1-2 Torr of helium bath gas. Supporting measurements based on laser induced fluorescence studies of OH recycling in the OH/CHCHO/O system are consistent with the PIMS study. Master equation calculations suggest that the origin of the methyl radicals is from prompt dissociation of chemically activated acetyl products and hence is consistent with previous studies which have shown that abstraction, rather than addition/elimination, is the sole route for the OH + acetaldehyde reaction.

Kinetics of CH2OO reactions with SO2, NO2, NO, H2O and CH3CHO as a function of pressure.

Kinetics of CH2OO Criegee intermediate reactions with SO2, NO2, NO, H2O and CH3CHO and CH2I radical reactions with NO2 are reported as a function of pressure at 295 K. Measurements were made under pseudo-first-order conditions using flash photolysis of CH2I2-O2-N2 gas mixtures in the presence of excess co-reagent combined with monitoring of HCHO reaction products by laser-induced fluorescence (LIF) spectroscopy and, for the reaction with SO2, direct detection of CH2OO by photoionisation mass spectrometry (PIMS). Rate coefficients for CH2OO + SO2 and CH2OO + NO2 are independent of pressure in the ranges studied and are (3.