The vapour phase reactions of formaldehyde, formaldehyde-d2, 13C-formaldehyde, acetaldehyde, acetaldehyde-1-d1, acetaldehyde-2, 2, 2-d3, and acetaldehyde-d4 with Cl and Br atoms were studied at 298±2 K and 1013±10 hPa using long-path FTIR detection. For formaldehyde the only products observed were HCl, HBr and CO; for acetaldehyde the product distribution suggests one dominant channel: CH3CHO+ X→ CH3CO+ HX. The ...