Absolute photoionization cross-section of the propargyl radical

Abstract

Using synchrotron-generated vacuum-ultraviolet radiation and multiplexed time-resolved photoionization mass spectrometry we have measured the absolute photoionization cross-section for the propargyl (C(3)H(3)) radical, σ(propargyl) (ion)(E), relative to the known absolute cross-section of the methyl (CH(3)) radical. We generated a stoichiometric 1:1 ratio of C(3)H(3):CH(3) from 193 nm photolysis of two different C(4)H(6) isomers (1-butyne and 1,3-butadiene). Photolysis of 1-butyne yielded values of σ(propargyl)(ion)(10.213 eV)=(26.1±4.2) Mb and σ(propargyl)(ion)(10.413 eV)=(23.4±3.2) Mb, whereas photolysis of 1,3-butadiene yielded values of σ(propargyl)(ion)(10.213 eV)=(23.6±3.6) Mb and σ(propargyl)(ion)(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.

Formation of fulvene in the reaction of C2H with 1,3-butadiene

“…The absence of CH 3 signal is likely due to the fact that the photoionization cross-section of CH 3 is much smaller than that of propargyl radicals; at 10.413 eV, for example, it is around 4 times lower [56]. In addition, the mass discrimination factor of the mass-spectrometer means detection of species with m/z = 39 is nearly twice as likely as species with m/z = 15 [56]. The majority of the signal at m/z = 52, vinyl acetylene, is due to 1,3-butadiene photolysis, Scheme 3 in Fig.…”

“…4 [55]. The peaks at m/z = 39 and 52 have been identified as propargyl radicals [56] (C 3 H 3 ), Fig. 3(b), and vinyl acetylene [54] (C 4 H 4 ), Fig.…”

Pyrolysis of furan in a microreactor

“…The origin is observed at 8.7 eV, the known threshold for propargyl radical. 24 The measured PIE curve for propargyl radical 29 is plotted in the solid, black scan and matches the PIE(m/z 39) resulting from furan pyrolysis until about 10 eV.…”

“…4 is a plot of the measured photoionization cross sections for carbon monoxide, 28 acetylene, 21 propargyl radical, 29 methylacetylene, 30 ketene, 31 and furan. 31 The cross sections for ketene and acetylene only overlap in a small window, 11.4-11.7 eV.…”

“…K. The PIMS for the dilution study at 11.0 eV sampled 5,000,000 mass spectra, compared to 100,000 for most other mass spectra, including the PIMS at 11.7 eV. are collected together in a single plot; carbon monoxide, 28 acetylene, 21 propargyl radical, 29 methylacetylene, 30 ketene, 31 and furan. 31 In order to eliminate the need for the photon flux correction term, Φ(E), the ratios were calculated in regions where the reported photoionization cross-section of one molecule of interest overlapped another molecule.…”