TIME-RESOLVED O-3 CHEMICAL CHAIN-REACTION KINETICS VIA HIGH-RESOLUTION IR LASER-ABSORPTION METHODS

Excimer laser photolysis in combination with time-resolved IR laser ab sorption detection of OH radicals has been used to study O-3/OH(v = 0) /HO2 chain reaction kinetics at 298 K, (i.e., OH + O-3 -->(k1) HO2 + O -2 and HO2 + O-3 -->(k2) OH + 2O(2)). From time-resolved detection of OH radicals with high-resolution near IR laser absorption methods, the chain induction kinetics have been measured at up to an order of magn itude higher ozone concentrations ([O-3] less than or equal to 10(17) molecules/cm(3)) than accessible in previous studies. This greater dyn amic range permits the full evolution of the chain induction, propagat ion, and termination process to be temporally isolated and measured in real time. An exact solution for time-dependent OH evolution under ps eudo-first-order chain reaction conditions is presented, which correct ly predicts new kinetic signatures not included in previous OH + O-3 k inetic analyses. Specifically, the solutions predict an initial expone ntial loss (chain ''induction'') of the OH radical to a steady-state l evel ([OH](ss)), with this fast initial decay determined by the slim o f both chain rate constants, k(ind) = k(1) + k(2). By monitoring the c hain induction feature, this sum of the rate constants is determined t o be k(ind) = 8.4(8) x 10(-14) cm(3) molecule(-1) s(-1) for room tempe rature reagents. This is significantly higher than the values currentl y recommended for use in atmospheric models, but in excellent agreemen t with previous results from Ravishankara et al. [J. Chem. Phys. 1979, 70, 984].