A SHOCK-TUBE STUDY OF CO-]CO2+H AND HNCO+OH-]PRODUCTS VIA SIMULTANEOUS LASER ADSORPTION MEASUREMENTS OF OH AND CO2(OH)

The rate coefficients for the reactions (1) CO + OH --> CO2 + H (2) HN CO + OH --> Products (2a) HNCO + OH --> CO2 + NH2 were determined usin g mixtures of HNO3/CO/Ar and HNO3/HNCO/Ar in incident shock wave exper iments. Simultaneous OH and CO2 absorption time-histories were obtaine d via cw uv narrow-linewidth absorption at 32606.56 cm(-1) (lambda = 3 06.687 nm) and cw infrared narrow-linewidth absorption at 2380.72 cm(- 1) (lambda = 4.2004 mu m), respectively. The measurements of k(1) dete rmined from measured CO2 time-histories are in good agreement with tho se determined from previous measurements of OH time-histories at this laboratory. The rate coefficient for the overall reaction of HNCO + OH --> Products was determined from analysis of OH data traces. The unce rtainty in k(2) was found to be +22%, -16%. By incorporating data from a previous low-temperature study, the following empirical expression was determined for the bimolecular reaction: k(2) = 3.63 x 10(7) T-1.5 exp(-1809/T)[cm(3) mol(-1) s(-1)] over the temperature range 620-1860 K. From analysis of CO2 data traces, an upper limit on the branching fraction (alpha = k(2a)/k(2)) for reaction (2a) of 10% was found, inde pendent of temperature over the range 1250-1860 K. (C) 1996 John Wiley & Sons, Inc.