The Ultraviolet Photochemistry of Diacetylene with Styrene

Abstract

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 2 061 0 band of the 1Δu ← X1Σ+ 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 (∼20 μs). 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.

The excited states and vibronic spectroscopy of diphenyldiacetylene and diphenylvinylacetylene

“…For example, both diacetylene (C 4 H 2 ) and phenyldiacetylene (PhC 4 H) exhibit broad absorption features under jet-cooled conditions, and no gas-phase fluorescence spectra of either molecule have been collected. 39,40 While the pure polyene and polyyne families have been studied extensively, much less is known about enyne bridges. Our recent studies of the spectroscopy and isomerization of trans-and cis-phenylvinylacetylene (PVA) have led to the conclusion that the vinylacetylene substituent produces vibronic spectra similar in many ways to those of styrene and stilbene.…”

H elimination and metastable lifetimes in the UV photoexcitation of diacetylene

“…After excitation of the 1 ⌬ u excited state, secondary reactions were found to lead to the formation of various larger hydrocarbons (12, 14, 15). The laser-based studies, principally at 231 and 243 nm, also found no evidence for radical products proceeding from primary photodissociation of diacetylene (1,11,(16)(17)(18). Although triplet diacetylene reactions invoked to account for the observed chemistry are now often incorporated in models of Titan's atmosphere, with an assumed metastable lifetime of 1 ms or more, to clarify their role, the triplet lifetime must be measured directly and as a function of excitation energy (19).…”

Forming Aromatic Hemispheres on Transition‐Metal Surfaces

“…We describe the interaction of hexabenzocoronene (1, HBC, Figure 1 a) [1] with a clean ruthenium surface. Interest in 1 and its interaction with transition-metal surfaces is driven by its relationship to the end cap of a carbon nanotube, to polynuclear aromatic hydrocarbons, [2][3][4][5][6][7][8] and to reactor carbonization. [9] Even though 1 is a large and multifunctional molecule, its high symmetry (there are only five types of C atom) simplifies the interpretation of the fundamental surface-molecule chemistry.…”