Reaction of Hydroxyl Radicals with C4H5N (Pyrrole): Temperature and Pressure Dependent Rate Coefficients

Abstract

Absolute (pulsed laser photolysis, 4−639 Torr N2 or air, 240−357 K) and relative rate methods (50 and 760 Torr air, 296 K) were used to measure rate coefficients k1 for the title reaction, OH +C4H5N → products (R1). Although the pressure and temperature dependent rate coefficient is adequately represented by a falloff parametrization, calculations of the potential energy surface indicate a complex reaction system with multiple reaction paths (addition only) in the falloff regime. At 298 K and 760 Torr (1 Torr = 1.33 mbar) the rate coefficient obtained from the parametrization is k1 = (1.28 ± 0.1) × 10−10 cm3 molecule−1 s−1, in good agreement with the value of (1.10 ± 0.27) × 10−10 cm3 molecule−1 s−1 obtained in the relative rate study (relative to C5H8, isoprene) at this temperature and pressure. The accuracy of the absolute rate coefficient determination was enhanced by online optical absorption measurements of the C4H5N concentration at 184.95 nm using a value σ184.95nm = (1.26 ± 0.02) × 10−17 cm2 molecule−1, which was determined in this work.