Laser-Induced Fluorescence Spectra of 4-Methylcyclohexoxy Radical and Perdeuterated Cyclohexoxy Radical and Direct Kinetic Studies of Their Reactions with O_2

摘要

The laser-induced fluorescence (LIF) excitation spectra of the 4-methylcyclohexoxy and dll-cyclohexoxy radicals have been measured for the first time.LIF intensity was used as a probe in direct kinetic studies of the reaction of O_2 with trans-4-methylcyclohexoxy and d11-cyclohexoxy radicals from 228 to 301 K.Measured rate constants near room temperature are uniformly higher than the Arrhenius fit to the lower-temperature data,which can be explained by the regeneration of cyclic alkoxy radicals from the product of their beta-scission and the effect of O_2 concentration on the extent of regeneration.The Arrhenius expressions obtained over more limited ranges were k_O_2=(1.4_(-1)~(+8)) x 10~(-13) exp[(-810+-400)/T] cm~3 molecule~(-1) s~(-1) for trans-4-methylcyclohexoxy (228-292 K) and k_O_2=(3.7_(-1)~(+4)) x 10~(-14) exp )[(-760+-400) /T] cm~3 molecule~(-1) s~(-1) for d11-cyclohexoxy (228-267 K) independent of pressure in the range 50-90 Torr.The room-temperature rate constant for the reaction of trans-4-methylcyclohexoxy radical with O_2 (obtained from the Arrhenius fit) is consistent with the commonly recommended value,but the observed activation energy is approx3 times larger than the recommended value of 0.4 kcal/mol and half the value previously found for the reaction of normal cyclohexoxy radical with O_2.