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The kinetics of the C 2 H 5 + Cl 2 , n-C 3 H 7 + Cl 2 , and n-C 4 H 9 + Cl 2 reactions has been studied at temperatures between 190 and 360 K using laser photolysis/photoionization mass spectrometry. Decays of radical concentrations have been monitored in time-resolved measurements to obtain reaction rate coefficients under pseudo-first-order conditions. The bimolecular rate coefficients of all three reactions are independent of the helium bath gas pressure within the experimental range (0.5-5 Torr) and are found to depend on the temperature as follows (ranges are given in parenthesis): k(C 2 H 5 + Cl 2 ) = (1.45 ± 0.04) × 10 −11 (T /300 K) −1.73 ± 0.09 cm 3 molecule −1 s −1 (190-359 K), k(n-C 3 H 7 + Cl 2 ) = (1.88 ± 0.06) × 10 −11 (T /300 K) −1.57 ± 0.14 cm 3 molecule −1 s −1 (204-363 K), and k(n-C 4 H 9 + Cl 2 ) = (2.21 ± 0.07) × 10 −11 (T /300 K) −2.38 ± 0.14 cm 3 molecule −1 s −1 (202-359 K), with the uncertainties given as one-standard deviations. Estimated overall uncertainties in the measured bimolecular reaction rate coefficients are ±20%. Current results are generally in good agreement with previous experiments. However, one former measurement for the bimolecular rate coefficient of C 2 H 5 + Cl 2 reaction, derived at 298 K using the very low pressure reactor method, is significantly lower than obtained in this work

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Intracavity laser absorption spectroscopy was used to measure the absorption spectra of a premixed, flat methane/air flame at a total pressure of 30 Torr. The spectra were measured in the spectral range of 16 000–16 300 cm−1. A flat flame burner was placed inside the cavity of a broadband dye laser pumped by a cw argon-ion laser. The spectrum of the laser output was measured by a high resolution spectrograph (with a spectral resolution of 0.003 nm). The spectrum of HCO radicals (Ã 2A′′←X̃ 2A transition) was measured with a high signal-to-noise ratio at different positions above the burner, providing the first quantitative measurement of the absolute concentrations of the HCO radical in flames. The linewidths of the individual rotational lines in the spectrum can be closely fitted by the equation Γ=X+ZN2(N+1)2, where X=0.37±0.03 cm−1 and Z=(8±0.5)10−6. The rotational temperature of the HCO radicals was evaluated from the spectra, but the error and the data scatter are relatively high since the lines with a high rotational quantum number N are strongly superimposed with lines from different branches. The “hot band,” which can be assigned to the transition (0,0,1)–(0,9,1), was observed in spectra measured at high temperature. The value ν3″=1859 cm−1 is evaluated from the position of this “hot band.” The concentration profile of the HCO radical has a maximum value of about 1.2×1013 molecules/cm3 which is in reasonable agreement with computer simulation results, when the uncertainties of the absorption cross section and of the rate constants for HCO reactions are taken into account. The relatively strong lines of the CH2 radical spectrum (the b̃ 1B1←ã 1A1 transition) were also recorded in the studied wavelength range. The spectra of these two radicals can be measured simultaneously which is advantageous in combustion diagnostics.

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