The strong enhancement of H-atom UV-photogeneration is revealed in van der Waals complexes of unsaturated hydrocarbons RH (RH=ethylene C2H4, propylene C3H6, butadiene C4H6, butene-2 C4H8) with oxygen RH-O-2 as compared with the 'free' RH molecules. The results obtained indicate enhancement of H atom yield to be due to one-quantum photoprocess (RH)-R-1-O-3(2) + h nu -> 3RH* + O-3(2)(O-1(2)) providing triplet RH molecules with excitation level sufficient for dissociation. (C) 2013 Elsevier B.V. All rights reserved.