Direct Kinetic Studies of Reactions of 3-Pentoxy Radicals with NO and O2

Abstract

Kinetic studies of the reactions of 3-pentoxy with NO and O2 have been performed using laser-induced fluorescence detection of 3-pentoxy radicals. Experiments were carried out at a total pressure of 50 Torr at subambient temperatures. Arrhenius expressions are obtained for the reactions of 3-pentoxy with NO (kNO) and O2 (kO2): kNO = (5.6 ± 1.6) × 10-13 exp[(7.8 ± 0.6) kJ mol-1/RT] cm3 molecule-1 s-1 (216−276 K), and kO2 = (4.1 ± 1.2) × 10-15 exp[(2.6 ± 0.6) kJ mol-1/RT] cm3 molecule-1 s-1 (220−285 K). No pressure dependence was observed for either rate constant at 243 K between 50 and 150 Torr. The negative temperature dependence of kNO is significantly larger than that of other alkoxy radicals, and this suggests a 298 K rate constant that is only one-third to half those measured for other alkoxy radicals. The small negative temperature dependence of kO2 is different from the small positive temperature dependence observed for ethoxy and propoxy radicals but is comparable to that previously observed for 2-butoxy radicals. The observed temperature dependencies of kNO and kO2 confound expectations that the kinetics of the reactions of larger alkoxy radicals would be very similar to the kinetics of C1−C3 alkoxy radicals.