A spectroscopic, kinetic, and product study of the (CH3)(2)C(OH)CH2O2 radical self-reaction and reaction with HO2

A flash photolysis technique was used to measure the UV absorption spectrum of the peroxy radical (CH3)(2)C(OH)CH2O2 formed in the (CH3)(3)COH/Cl/O-2 reaction system and to study the kinetics of its self reaction and reaction with the HO2 radical at room temperature and above: 2(CH3)(2)C(OH)CH2O2 --> 2(CH3)(2)C(OH)CH2O + O-2 (5a); 2(CH3)(2)C(OH)CH2O2 --> (CH3)(2)C(OH)CH2OH + (CH3)(2)C(OH)CHO + O-2 (5b); (CH3)(2)C(OH)CH2O2 + HO2 --> (CH3)(2)C(OH)CH2OOH + O-2 (8). The spectrum of the radical resembles that of other beta-hydroxyl substituted peroxy radicals in form and magnitude. Use of this and other known absorption cross sections in an appropriate chemical model of the system allowed k(5), the branching ratio alpha (=k(5a)/k(5)), and k(8) to be derived as a function of temperature (T = 306-398 K) by an iterative procedure involving the simulation of experimental decay traces recorded at several wavelengths: k(5) = (1.4 +/- 0.6) x 10(-14) exp[(1740 +/- 150)K/T) cm(3) molecule(-1) s(-1); alpha = 0.59 +/- 0.15 (no discernible temperature dependence over this range); k(8) = (5.6 +/- 2.0) x 10(-14) exp[(1650 +/- 130)K/T) cm(3) molecule(-1) s(-1). These expressions yield values for k(5) and k(8) of 4.8 and 14 x 10(-12) cm(3) molecule(-1) s(-1) at 298 K, confirming the phenomena both of enhanced self reaction reactivity upon beta-OH substitution and of a large rate coefficient for the reaction of all greater than or equal to C-2 peroxy radicals with HO2. Product studies of reaction 5, using an FTIR-smog chamber system, confirmed the assumed reaction mechanism in 700 Torr of air at 296 K, namely the unique formation of the peroxy radical of interest, rapid decomposition of the alkoxy radical (formed in reaction 5a) through C-C bond scission, and subsequent reaction with O-2 to yield formaldehyde and acetone (and HO2). A similar fate for the (CH3)(2)C(OH)CH2O radical is expected as part of the degradation of tert-butyl alcohol (TBA) and isobutene under tropospheric conditions. Furthermore, the product distribution results, when combined with the extrapolated k(5) and k(8) values, allow alpha be determined as 0.60 +/- 0.07 at 296 K, consistent with the value obtained from the flash photolysis study. As part of the smog chamber work, a relative rate technique was used to measure the rate coefficient for the reaction of Cl atoms with (CH3)(2)C(CH2Cl)OH as (9.2 +/- 1.1) x 10(-12) cm(3) molecule(-1) s(-1) at 296 K.