Sublimation and dissociation of cyanuric acid particles and dissociation of isocyanic acid vapor

The sublimation and subsequent dissociation of cyanuric acid particles (HNCO)(3) and the thermal decomposition of isocyanic acid (HNCO) were investigated behind incident and reflected shock waves at high temperatures. In a first series of experiments, the shock-induced sublimation and dissociation of cyanuric acid particles was studied by particle light scattering and by OH and CO absorption measurements. Scattered light intensities were used to monitor the particle size decrease at temperatures 540 K < T < 630 K. Formation of OH was detected by ring-dye laser spectroscopy at the line center of the Q(1)(5) rotational line in the (0-0) band of the OH A(2)Sigma(+) <-- X(2)Pi(+) transition, at v = 32403.405 cm(-1). An apparent rate coefficient of (HNCO)(3) --> OH + products k(2,app) = 1.5 x 10(7) exp(-197 kJmol(-1)/RT) s(-1) was determined from the initial slope of the measured OH concentration profiles at temperatures 2290 K < T < 3830 K. Significant CO absorption was not found in these experiments. In a second series of experiments, HNCO decomposition was studied in the temperature range 2200 K < T < 2800 K in mixtures containing 0.74%-0.9% HNCO in argon. Decomposition was followed by CO absorption measurements using an infrared (IR)-diode laser spectrometer rapidly tuned over the (0-1) R30 vibrational-rotational line of CO at the wavenumber v = 2244.37722 cm(-1). The resulting absorption profiles were evaluated in terms of concentrations of the expected decomposition product CO. The rate coefficient of HNCO + Ar --> CO + NH + Ar k(3) = 9.0 x 10(14) exp(-295 kJmol(-1)/RT) cm(3) mol(-1) s(-1) was determined from the concentration profiles.