Direct detection of polyynes formation from the reaction ofethynyl radical (C2H) with propyne (CH3-C-CH) and allene(CH2=C=CH2)
The reactions of the ethynyl radical (C2H) with propyne and allene are studied at room temperature using an apparatus that combines the tunability of the vacuum ultraviolet radiation of the Advanced Light Source at Lawrence Berkeley National Laboratory with time-resolved mass spectrometry. The C2H radical is prepared by 193-nm photolysis of CF3CCH and the mass spectrum of the reacting mixture is monitored in time using synchrotron-photoionization with a dual-sector mass spectrometer. Analysis using photoionization efficiency curves allows the isomer-specific detection of individual polyynes of chemical formula C5H4 produced by both reactions. The product branching ratios are estimated for each isomer. The reaction of propyne with ethynyl gives 50-70% diacetylene (H-C{triple_bond}C-C{triple_bond}C-H) and 50-30% C5H4, with a C5H4-isomer distribution of 15-20% ethynylallene (CH2{double_bond}C{double_bond}CH-C{triple_bond}CH) and 85-80% methyldiacetylene (CH3-C{triple_bond}C-C{triple_bond}CH). The reaction of allene with ethynyl gives 35-45% ethynylallene, 20-25% methyldiacetylene and 45-30% 1,4-pentadiyne (HC{triple_bond}C-CH2-C{triple_bond}CH). Diacetylene is most likely not produced by this reaction; an upper limit of 30% on the branching fraction to diacetylene can be derived from the present experiment. The mechanisms of polyynes formation by these reactions as well as the implications for Titans atmospheric chemistry are discussed.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE Director. Office of Science. Office of Basic EnergySciences; National Aeronautics and Space Administration (NASA)
- DOE Contract Number:
- DE-AC02-05CH11231; NASA:NAGS-13339
- OSTI ID:
- 917405
- Report Number(s):
- LBNL-61760; R&D Project: 401001; BnR: KC0301020; TRN: US0804524
- Journal Information:
- Physical Chemistry Chemical Physics, Vol. 9; Related Information: Journal Publication Date: 2007; ISSN 1463-9076
- Country of Publication:
- United States
- Language:
- English
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