The atmospheric chemistry of the acetonoxy radical

The chemistry of the acetonoxy radical, CH3C(O)CH2O. formed in the atmosphe ric degradation of acetone, was studied dy a combination of experimental an d theoretical methods. In an environmental chamber study conducted over the temperature range 225-298 K, acetonoxy radical chemistry was shown to be d ominated by decomposition, CH3C(O)CH2O -> CH3C(O) + CH2O. No evidence was f ound for a reaction of this species with O-2, CH3C(O)CH2O + O-2 -> CH3C(O)C HO + HO2, even at 225 K in the presence of 1 atm O-2. In a theoretical ab i nitio and statistical kinetics investigation, the barrier to CH3C(O)CH2O de composition was found to be 6-7 kcal/mol. Using SSE theory and RRKM-based m aster equation analysis, it was determined that about 80% of the CH3C(O)CH2 O radicals formed in the CH3C(O)CH2O2 + NO reaction have sufficient energy to decompose "promptly" under tropospheric conditions. On the basis of TST theory and allowing for falloff, the dissociation rate of thermalized CH3C( O)CH2O radicals was found to be on the order of 5 x 10(7) s(-1) at 1 atm an d 300 K and 5 x 10(5) s(-1) at 0.2 atm and 220 K. The results confirm that the acetonoxy reaction with O-2 is always negligible in the troposphere, co nsistent with the experimental observations. As part of this study, the rat e coefficient for reaction of CI with acetone (k(2)) was measured by a rela tive rate technique, and a value of k(2) = (3.1 +/- 0.5) x 10(-11) exp(-815 +/- 150/T) cm(3) molecule(-1) s(-1) reported.