Matrix-isolation in low-temperature rare-gas matrices is a good technique for the spectroscopic characterization of radicals. This laboratory has recorded FTIR spectra for several hydrocarbon radicals that are thought to play a role as intermediates in the growth of hydrocarbon radicals in planetary atmospheres and the interstellar medium. The radicals were generated by the gas-phase pyrolysis of precursor molecules in a pulsed, hyperthermal nozzle at temperatures of 800-1500 K and then isolated in an argon matrix. Vibrational bands in the experimental spectra were matched to frequencies predicted by Gaussian 09. The 1-butyn-3-yl radical, a C4H5 isomer, was formed by the pyrolysis of gas-phase 3-bromo-1-butyne. Pyrolysis of 3-methyl-1-butyne was also investigated as a possible pyrolytic precursor to the 1-butyn-3-yl radical. Evidence of 1-butyn-3-yl formation was observed, but the experimental spectra were searched for other radicals as well. Another isomer of C4H5, the 2-butyn-1-yl radical, was isolated following the pyrolysis of 1-bromo-2-butyne. The precursor was found to be a clean source of the radical at low temperatures. Finally, 2-chloro-2-butene was investigated as a possible pyrolytic precursor to a C4H7 radical isomer, 2-buten-2-yl. The experimental vibrational spectra of these radicals can serve as useful benchmarks for detection of hydrocarbon radicals in extraterrestrial environments and also inform future laboratory studies on astrochemical reactions involving these radicals.

Pyrolysis and matrix-isolation FTIR spectroscopy for characterization of astrochemically significant radicals

256th National Meeting (2018)

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