The reaction of acetaldehyde and propionaldehyde with hydroxyl radicals: experimental determination of the primary H2O yield at room temperature

The branching fraction of H-abstraction in the elementary reactions of acetaldehyde and propionaldehyde with OH at 290 K was determined directly using a fast-flow reactor coupled to a molecular beam sampling mass spectrometry apparatus. The primary-product H2O yield of the title reactions was quantified relative to that of the isobutane+OH reaction, and found to be 89±6 and 100±10% for the reactions of acetaldehyde+OH and propionaldehyde+OH, respectively. Furthermore, an upper limit of 3% could be determined for the yield of formic acid in the hypothetical addition/elimination reaction pathway. We conclude that the reaction of OH radicals with aldehydes proceeds predominantly, if not exclusively, via H-abstraction, forming H2O and RCO.