Spectroscopic and Kinetic Investigations of the Propargyl Radical Using Ultraviolet Cavity Ring-Down Spectroscopy
Dean B. Atkinson and Jeffrey W. Hudgens, J. Phys. Chem. A 103, 4242 (1999).

The ultraviolet absorption spectrum of the propargyl radical (H₂C-C-CH,) first reported by Ramsay and Thistlethwaite,¹ in the wavelength regions 290 nm - 345 nm was re-examined using the very sensitive, high resolution cavity ring-down spectroscopic (CRDS) technique. The radical was formed by excimer laser photolysis of propargyl chloride, propargyl bromide, methyl acetylene, and allene, all of which were observed to produce identical spectra. The absolute absorption cross-section, s _332.5 = 2.2 x10^-18 cm² was measured using chemical actinometry. No evidence of the predicted higher energy transitions was observed in the wavelength ranges 220 nm - 230 nm, 238 nm - 252 nm, or 264 nm - 282 nm, however a strong absorption due to chlorine atom addition products in the propargyl chloride system was observed near 240 nm. The self-reaction rate coefficient for the propargyl radical, k = 3.9 x10^-11 cm³s^-1, was found to be pressure independent for total pressures of helium between 200 and 10,000 Pa. The association reaction, C₃H₃ + O₂ (He, Ar, N₂) was investigated in pseudo-first order at 298 K for pressures between 200 and 10,000 Pa.

1. Ramsay, D. A. and Thistlethwaite, P., Can. J. Phys., 44, 1381-1386 (1966.)