A combined experimental and theoretical investigation of the reactions of 3-pentoxy radicals: Reaction with O-2 and unimolecular decomposition

The reactions of 3-pentoxy radicals with O-2 and their unimolecular decompo sition were investigated using time-resolved and simultaneous detection of NO2 and OH in the laser flash initiated oxidation of bromopentane combined with numerical simulation of the experimentally obtained concentration-time profiles. NO2 was monitored by cw-LIF, whereas OH was detected by laser lo ng-path absorption at 308 nm. 3-pentoxy radicals were produced selectively by the excimer-laser photolysis of 3-bromopentane at 248 nm and subsequent reaction of the 3-pentyl radicals with O-2 in the presence of NO. All exper iments were performed at a temperature of 293 +/- 3 K and 50 mbar total pre ssure. The following rate coefficients for reaction with oxygen (k(O2)) and for thermal decomposition (k(decomp)) of 3-pentoxy radicals were obtained: k(O2) = (7.2+/-3.5) x 10(-15) cm(3) molecule(-1) s(-1) and k(decomp) = (5. 0+/-2.5) x 10(3) s(-1). In addition to the experimental investigation, the unimolecular reaction ch annels of 3-pentoxy radicals were also analyzed by a combined ab initio/RRR M treatment. From the ab initio calculations structures of the 3-pentoxy ra dical and its decomposition transition states as well as energy barriers we re determined. This information was used to solve the J-independent Master Equation which allowed thermal decomposition rate coefficients to be determ ined. The calculated rate constants are in good agreement with those determ ined experimentally.