PHOTODISSOCIATION OF CYANOACETYLENE - APPLICATION TO THE ATMOSPHERIC CHEMISTRY OF TITAN

The quantum yield and reaction threshold for the photochemical dissoci ation of cyanoacetylene into a hydrogen atom and the cyanoethynyl radi cal have been determined. The quantum yield at 185 nm is similar to 0. 09. The threshold is similar to 240 nn. Combination of this data with literature values shows that production of excited-state cyanoacetylen e is the major primary process resulting from irradiation between 185 and 254 nm. Also determined are the relative rate constants for the ab straction of a hydrogen atom from hydrogen, methane, and ethane by the cyanoethynyl radical (k(H-2):k(CH4):k(C2H6) = 1:9.3:63). Implications of these results for the proposal that hydrogen abstraction plays an important role in the conversion of methane to ethane and in the prote ction of unsaturated compounds from photoconsumption in the atmosphere of Titan are discussed. (C) 1995 Academic Press, Inc.