The UV absorption spectrum along with the self-reaction and oxidation reaction kinetics of the hydroxycyclohexadienyl radical, C6H6OH (which results from OH addition to benzene), were studied using excimer laser photolysis coupled to transient UV absorption. The radicals were generated by photolysis of N2O/H2O/ C6H6/He mixtures at 193 nm in a series of chemical reactions initiated by O(1D). The radical has continuous absorption in the range 260-340 nm with a maximum absorption cross-section of (8.1 ± 1.4) × 10-18 cm2 molecule-1 at 280 nm. Reaction of the radical with molecular oxygen, C6H6OH + O2 ⇌ C6H6(OH)OO (1), and self-reaction C6H6OH + C6H6OH → products (2), were studied over the 252-285 K temperature range at 1.01 ± 0.02 bar (He). The radical temporal profiles were recorded via transient absorption at 315 nm. In reaction 1, two-time-domain "equilibration" kinetics were recorded in the temperature range 252-273 K. The rate constant of the addition reaction is k1 = (1.4 ± 0.8) × 10-12 exp(-18.6 ± 1.7 kJ mol-1/RT) cm3 molecule-1 s-1. The standard enthalpy of reaction 1 was determined from the measured equilibrium constants using the third law method: ΔH298o = -43.6 ± 2.0 kJ mol-1. The measured rate constant of self-reaction 2 is k2 = (6 ± 3) × 10-11 exp(-2.00 ± 1.6 kJ mol-1/RT) cm3 molecule-1 s-1.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry