Absolute photoionization cross-section of the propargyl radical

Using synchrotron-generated vacuum-ultraviolet radiation and multiplexed time-resolved photoionization mass spectrometry we have measured the absolute photoionization cross-section for the propargyl (C3H3) radical, σpropargylion(E), relative to the known absolute cross-section of the methyl (CH3) radical. We generated a stoichiometric 1:1 ratio of C3H3 : CH3 from 193 nm photolysis of two different C4H6 isomers (1-butyne and 1,3-butadiene). Photolysis of 1-butyne yielded values of σpropargylion(10.213 eV)=(26.1±4.2) Mb and σpropargylion(10.413 eV)=(23.4±3.2) Mb, whereas photolysis of 1,3-butadiene yielded values of σpropargylion(10.213 eV)=(23.6±3.6) Mb and σpropargylion(10.413 eV)=(25.1±3.5) Mb. These measurements place our relative photoionization cross-section spectrum for propargyl on an absolute scale between 8.6 and 10.5 eV. The cross-section derived from our results is approximately a factor of three larger than previous determinations.