The rate coefficient of the C₃H₃ + C ₃H₃ reaction from UV absorption measurements after photolysis of dipropargyl oxalate

The kinetics of the C₃H₃ + C₃H ₃ reaction was investigated by using dipropargyl oxalate (DPO) as a new, halogen-free photolytic source for propargyl radicals in the gas phase. After laser-flash photolysis of DPO at 193 nm, the initial absorbance was determined at different wavelengths, and the results were compared with values obtained in analogous experiments using propargyl halides as precursors. A satisfactory agreement of the absorbances was found between 295 and 355 nm but differences were observed near 242 nm. The latter wavelength has also been proposed for C₃H₃ detection. Our results, however, indicate that this absorption is probably due to halogen-containing species. The rate coefficient of the C₃H₃ + C₃H ₃ reaction was then determined from time-resolved absorption measurements at 332.5 nm with DPO as precursor. Values of (2.7 ± 0.6) × 10^-11 cm³ molecule^-1 s^-1 at 373 K, (2.8 ± 0.6) × 10^-11 cm³ molecule ^-1 s^-1 at 425 K, (3.5 ± 0.8) × 10 ^-11 cm³ molecule^-1 s^-1 at 500 K, and (4.1 ± 0.8) × 10^-11 cm³ molecule ^-1 s^-1 at 520 K were obtained with no significant pressure dependence between 1 and ca. 100 bar (140 bar for T = 373 K).