Further studies of exponential branching rates in reflected-shock heated, nonstoichiometric H2COO2 systems

More thorough measurements are made of exponentially growing chemiluminescence, viewed end-on, during branched-chain ignition of H 2 CO O 2 Ar mixtures in reflected shock waves, to try to resolve residual questions from earlier studies by this and related techniques. Systematic variations of spectral bandpass, gas composition, and gas pressure have been made for particular H 2 :O 2 ratios and temperature spans. At H 2 :O 2 = 1/3, with CO present, exponential time constants, * , for the CO O chemiluminescence are independent of spectral bandpass over the 300–600 nm range; with CO absent, there is appreciable H 2 O 2 system ultraviolet chemiluminescence at λ > 340 nm, whose presence voids some earlier interpretations predicated on dominance of the OH A 2 Σ + → X 2 Π spectrum. At H 2 :O 2 = 0.1, * of CO O chemiluminescence exhioits a small and unaccountable variation with extent of dilution of H 2 CO O 2 mixtures in noble gas. This effect, diminished but perceptible also at H 2 :O 2 = 1/3, clouds kinetic interpretation of * in lean mixtures, but of itself does not reconcile disagreements with infrared and with incident shock CO-O exponential rates. The dilution effect is not found at H 2 :O 2 = 10, where new measurements up to T = 2400 K are made and pooled with previous rich * results to determine, for H + O 2 → k a O H + O , 1250 T 2500 K , the expression: k a = 1.22 X 10 17 T − 0.907 exp ⁡ ( − 8369 / T ) c m 3 mole − 1 sec ⁡ − 1 .