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, sigma(ion)(propargyl) (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 sigma(ion)(propargyl) (10.213 eV) = (26.1 +/- 4.2) Mb and sigma(ion)(propargyl) (10.413 eV) = (23.4 +/- 3.2) Mb, whereas photolysis of 1,3-butadiene yielded values of sigma(ion)(propargyl) (10.213 eV) = (23.6 +/- 3.6) Mb and sigma(ion)(propargyl) (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. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3698282]