Allyl radical reactions with NO and NO2 were studied in direct, time-resolved experiments in a temperature controlled tubular flow reactor connected to a laser photolysis/photoionization mass spectrometer (LP-PIMS). In the C3H5 + NO reaction 1, a dependence on the bath gas density was observed in the determined rate coefficients and pressure falloff parametrizations were performed. The obtained rate coefficients vary between 0.30-14.2 × 10-12 cm3 s-1 (T = 188-363 K, p = 0.39-23.78 Torr He) and possess a negative temperature dependence. The rate coefficients of the C3H5 + NO2 reaction 2 did not show a dependence on the bath gas density in the range used (p = 0.47-3.38 Torr, T = 201-363 K), and they can be expressed as a function of temperature with k(C3H5 + NO2) = (3.97 ± 0.84) × 10-11 × (T/300 K) -1.55±0.05 cm 3 s-1. In the C3H5 + NO reaction, above 410 K the observed C3H5 radical signal did not decay to the signal background, indicating equilibrium between C3H 5 + NO and C3H5NO. This allowed the C 3H5 + NO â‡ C3H5NO equilibrium to be studied and the equilibrium constants of the reaction between 414 and 500 K to be determined. With the standard second- and third-law analysis, the enthalpy and entropy of the C3H5 + NO â‡ C3H5NO reaction were obtained. Combined with the calculated standard entropy of reaction (ΔS 298 = 137.2 J mol-1K-1), the third-law analysis resulted in ΔH 298 = 102.4 ± 3.2 kJ mol-1 for the C 3H5-NO bond dissociation enthalpy.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry