The ultraviolet photochemistry of diacetylene with styrene

The reaction of metastable diacetylene with styrene is explored using a molecular beam pump-probe time-of-flight (TOF) mass spectrometer. Diacetylene is laser-excited to the 2(0)(1)6(0)(1) band of the (1)Delta(u) <-- X(1)Sigma(g)(+) transition, whereupon rapid intersystem crossing occurs to the lowest triplet states. The triplet state diacetylene then reacts with styrene as the gas mixture traverses a short reaction tube (similar to20 mus). The reaction is quenched as the gas mixture expands into a vacuum where the primary photoproducts are probed using vacuum ultraviolet (VUV) photoionization, resonant two-photon ionization (R2PI), and UV-UV holeburning. The major products from the reaction have molecular formulas C10H8, C12H8, and C12H9. Two different C10H8 products have been identified as 1-phenyl-1-buten-3-yne and m-ethynyl styrene using UV-UV holeburning and comparing with spectra of authentic samples. Mechanisms for the formation of the above products are proposed on the basis of deuterium substitution studies of the reaction. The potential implications of these reactions for the formation of polycyclic aromatic hydrocarbons in sooting flames is discussed.