A SHOCK-TUBE STUDY OF THE REACTION H-2-]HNO+H(NO)

The high-temperature reaction of NO with H-2 has been studied behind r eflected shock waves in the temperature range of 1760-2160 K at total pressures of 1.4 to 2.0 bar by monitoring the time-dependent H-atom co ncentrations in the postshock reaction zone using atomic resonance abs orption spectroscopy (ARAS). Mixtures of NO and H-2 highly diluted in argon were used as initial reactants. The rate coeffficient, k(1), of the initiation reaction: NO + H-2 --> HNO + H has been determined from the measured initial H-atom concentration slopes to be k(1) = 1.5 x 1 0(13) exp(-26165K/T) cm(3) mol(-1) s(-1), taking the fast decompositio n of HNO into account. This direct determination of the rate coefficie nt k(1) was possible, because the contribution of H-2 dissociation to the total H atom concentration of the system was relatively small in t he temperature and concentration ranges of this study. Measured O-atom concentrations in the high-temperature H-2/NO/Ar reaction system (256 0 K less than or equal to T less than or equal to 4040 K) were sensiti ve to the reaction NO + H --> OH + N, resulting in an estimate of its rate coefficient. A simplified mechanism of 15 elementary reactions wa s able to predict all measured H and O atom profiles with reasonable a ccuracy.