Quantitative HNO detection behind shock waves

Knowledge about the high temperature kinetics of HNO, which represents a key species in NOx flame chemistry, is scarce. Using the very sensitive absorption based frequency modulation (FM) spectroscopy, HNO has been measured behind shock waves for the first time. The UV photolysis of glyoxal/NO mixtures at λ=193 nm served as an HNO source with stable HNO concentration plateaus generated via the fast initial formation of HCO radicals followed by the reaction HCO + NO → CO + HNO. FM line shapes of three selected transitions of the A˜1A′′(100)−X˜1A′(000) band of HNO have been recorded and their pressure broadening coefficient has been determined. By analyzing HNO and HCO concentration-time profiles measured under very similar reaction conditions it was possible to confirm an HCO/HNO formation mechanism and to determine the HNO absorption cross section. The expression log[σc(HNO,p=0bar,295K