The Cl-atomand HO-radical-initiated oxidation of CH2(OH)CHO was studied by the FTIR spectroscopic method in the steady-state photolyses ( > 300 nm) of mixtures containing ppm concentrations of CH2(OH)CHO and Cl2, and CH2(OH)CHO and C2H5ONO, respectively, in 700 Torr of N2-02. HCHO and CHO-CHO were observed as major initial products in both the Cl and HO reactions. In the presence of added N02, the former product was partially replaced by a transient species identified as CH2(0H)C(=0)00N02, while the CHO-CHO yield remained unchanged. The results are consistent with the occurrence of reactions la and lb followed by the subsequent oxidation of the ensuing radicals CH2(0H)C(=0) and CH(OH)CHO, i.e., CH2(OH)CHO + Cl (or HO) -CH2(0H)C(=0) + HCI [or H20] (la), CH2(OH)CHO + Cl (or HO) -* CH(ÓH)CHO + HCI [or H2Oj (lb). Values for fclb/[A:la + klb] were determined to be 0.35 and 0.22 for the Cl and HO reactions, respectively. Relative rate constants of ¿[Cl+CH3CHO]/fc[Cl+CH2(OH)CHO] = 0.9 and fc[HO+ CH3CHO]/fc[HO+CH2(OH)CHO] = 1.6 were also obtained. Some measurements are reported on the dependence of the dynamics of the oscillatory combustion of acetaldehyde in a CSTR upon reactant input rates. We map a kinetic phase diagram for the different types of behavior, stationary states and oscillations, found with nonequimolar input fluxes of acetaldehyde and oxygen. Hysteresis is observed in the transition from steady dark oxidation to oscillatory cool flames as the oxygen input flux is varied. We measure the dependence of the period and amplitude of the oscillatory cool flame light emission on both input fluxes. Under our conditions, the period of the oscillation is found to be more strongly dependent upon the acetaldehyde input rate than the oxygen input rate. These results compare favorably with calculations made with a five-variable, twelve-step model.

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Reactions of the Nitrate Radical with Olefins 1629 eter for an 0NC1-Ar collision is taken to be 4,09 Á then eq 5 becomes eq 6. The values of 2&lp and &2nd order are shown kLp = 1.76856 X 1017T-1/2 eXp(-38,000/RT) cc/mol sec (6)in Table II. The correspondence between the calculated and the experimental values especially at the higher temperatures is quite satisfying considering the simplicity of the approach. This correspondence is strong indication that under the present conditions in the shock tube the decomposition is proceeding essentially by the unimolecular (free radical) pathway. A further check on this conclusion is provided by a comparison of the values of the half-lives for reaction by the unimolecular (free radical) and bimolecular (molecular) pathways. A calculation using the rate constant expression of Ashmore and Burnett30 establishes that under present conditions the half-life of the molecular pathway is three orders of magnitude longer than the halflife of the free-radical pathway. This evidence then shows that ONC1 is decomposing by means of a unimolecular mechanism and that under present conditions (i.e., high dilution in argon) it is at or near low pressure conditions.

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