Temperature and Pressure Dependent Kinetics of QOOH Decomposition and Reaction with O2: Experimental and Theoretical Investigations of QOOH Radicals Derived from Cl + (CH3)3COOH

Abstract

QOOH radicals are key species in autoignition, produced by internal isomerizations of RO2 radicals, and are central to chain branching reactions in lowerature combustion. The kinetics of QOOH radical decomposition and reaction with O2 have been determined as a function of temperature and pressure, using observations of OH radical production and decay following H-atom abstraction from t-butyl hydroperoxide ((CH3)3COOH) by Cl atoms to produce QOOH (CH2(CH3)2COOH) radicals. The kinetics of QOOH decomposition have been investigated as a function of temperature (251-298 K) and pressure (10-350 Torr) in helium and nitrogen bath gases, and those of the reaction between QOOH and O2 have been investigated as a function of temperature (251-304 K) and pressure (10-100 Torr) in He and N2. Decomposition of the QOOH radical was observed to display temperature and pressure dependence, with a barrier height for the decomposition of (44.7 ± 4.0) kJ mol-1 determined by master equation fitting to the experimental data. The rate coefficient for the reaction between QOOH and O2 was determined to be (5.6 ± 1.7) × 10-13 cm3 s-1 at 298 K, with no significant dependence on pressure, and can be described by the Arrhenius parameters A = (7.3 ± 6.8) × 10-14 cm3 s-1 and Ea = -(5.4 ± 2.1) kJ mol-1 in the temperature range of 251-304 K. This work represents the first measurements of any QOOH radical kinetics as a function of temperature and pressure.