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Issue 23, 2002
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Quantitative detection of HCO behind shock waves: The thermal decomposition of HCO

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Using FM spectroscopy formyl radicals were detected for the first time behind shock waves. HCO radicals have been generated by 308 nm photolysis of mixtures of formaldehyde in argon. The HCO spectrum of the (Ã2A″ ← [X with combining tilde]2A′) (0900 ← 0010) transition was measured at room temperature with high resolution and the predissociative linewidths Γ of the individual rotational lines were fitted to Γ = X + ZN2(N′ + 1)2, where X = 0.22 cm−1 and Z = 1.0 × 10−5 cm−1. Since FM spectroscopy is very sensitive to small line shape variations the spin splitting in the Q-branch could be resolved.

Time resolved measurements of HCO profiles at temperatures below 820 K provided the temperature independent rates of reaction (4), H + HCO → H2 + CO, and reaction (5), HCO + HCO → CH2O + CO, k4 = 1.1 × 1014 cm3 mol−1 s−1k5 = 2.7 × 1013 cm3 mol−1 s−1and the low pressure room temperature absorption cross section of the Q(9)P(2) line at 614.872 nm, αc = (1.5 ± 0.4) × 106 cm2 mol−1 (base e).

Measurements of the unimolecular decomposition of HCO, reaction (3) HCO + M → H + CO + M, were performed at temperatures from 835 to 1230 K and at total densities from 3.3 × 10−6 to 2.5 × 10−5 mol cm−3. They can be represented by the following Arrhenius expression. k3 = 4.0 × 1013·exp(−65 kJ mol−1/RT) cm3 mol−1 s−1 (Δ log k3 = ±0.23)The corresponding RRKM fit, 4.8 × 1017·(T/K)−1.2·exp(−74.2 kJ mol−1/RT) cm3 mol−1 s−1 (600 < T/K < 2500), supports the lower range of previously reported high temperature rate expressions.

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Publication details

The article was received on 12 Jun 2002 and first published on 22 Oct 2002

Article type: Paper
DOI: 10.1039/B205692E
Citation: Phys. Chem. Chem. Phys., 2002,4, 5778-5788
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    Quantitative detection of HCO behind shock waves: The thermal decomposition of HCO

    G. Friedrichs, J. T. Herbon, D. F. Davidson and R. K. Hanson, Phys. Chem. Chem. Phys., 2002, 4, 5778
    DOI: 10.1039/B205692E

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