The reaction of HNCO with NO₂ in shock waves

The reaction of HNCO with NO₂ has been studied with a shock tube equipped with two stabilized CW CO lasers. Three key products, CO, NO and H₂O, measured by time-resolved resonance absorption, have been kinetically modeled using a mechanism consisting of seventy four reactions. The modeling, aided by sensitivity analysis, reveals that the rates of formation of both CO and H₂O depend strongly on the rate of the O+HNCO reaction, which occurs by the two major channels: O+HNCO→NH+CO₂ (2) and OH+NCO (3). The third channel producing HNO+CO is unimportant according to the result of our BAC-MP4 calculations. The rate constants obtained from the modeling agree closely with those measured by Mertens et al. (Ref. 7) using different diagnostics. TST fittings to these two sets of kinetic data, using the transition state structures and frequencies computed by the BAC-MP4 method, give rise to k₂=9.8×10⁷T^1.41 e^-4.290/T cm³/mol.s k₃=2.2×10⁶T^2.11 e^-5,750/T cm³/mol.s covering the temperature range 300-3000 K. The calculated values for the total rate constant (k₂+k₃) at 679 and 741 K agree closely with those reported by Tully, Perry and coworkers (Ref. 18). Our result successfully bridges the large gap existed between the two temperature regimes, providing much needed data around 1000 K for RAPRENO_x applications.