Effect of Spectral Line Shape on Apparent Rotational Temperatures of OH

The effect of spectral line shape on apparent rotational temperatures of OH has been investigated for the P_1 branch, ^2Σ-->^2π transitions, (0, 0) band, by treating the ratio of collision half-width to Doppler half-width as a variable parameter. The results of calculations for emission experiments, using conventional plots, show a large effect of line shape on apparent temperature. In general, the greater the ratio of collision half-width to Doppler half-width, the smaller the distortion of experimental data. The analysis predicts higher apparent rotational temperatures for isothermal systems at reduced pressures than at atmospheric pressures. Although this result is in agreement with experimental observations on flames, it cannot be used as an explanation for the observed data without auxiliary studies proving that distortion of data is of importance in any given case. The two-path method for determining temperatures and emissivities (concentrations) in flames has been extended to spectral lines with combined Doppler- and collision-broadening

Oscillator strengths of the ultraviolet γ bands of NO

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Spectroscopy methods of temperature measurements

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On the Validity of Anomalous Population Temperatures in Flames

It should be obvious to anyone reading our recent papers objectively that our "principle thesis" was (a) to examine the origin of the basic relations involved in the customary procedure for the determination of population temperatures in flames, with emphasis on the effect of spectral line shape on the final equations, and (b) to present experimental data on low pressure combustion flames which support the earlier experimental findings of Gaydon and Wolfhard

Determination of Absolute ƒ Values from Relative Intensity Measurements for Spectral Lines with Doppler Contour

The experimental determination of absolute intensities for isolated spectral lines or for entire vibration-rotation bands involves formidable experimental difficulties. For this reason it is highly desirable to consider the use of techniques which permit the determination of absolute f values from relative intensity measurements performed by the use of a low resolution spectrograph. It is the purpose of this note to call attention to a useful experimental procedure for spectral lines with Doppler contour and for optical densities which are sufficiently large to assure a nonlinear dependence of intensity on optical density. The method is a generalization of a two-path experiment proposed for emission studies on flames

Quantitative Studies of Apparent Rotational Temperatures of OH in Emission and Absorption (Spectral Lines with Doppler Contour)

Even if a Boltzmann distribution exists for the population of molecules in various energy levels, it is not possible to obtain a satisfactory interpretation of experimental data by the use of conventional procedures unless the product of maximum spectral absorption coefficient P_(max) and optical density χ is sufficiently small. Detailed calculations are presented which show that the experimental results, which suggest an anomalous rotational temperature for the ^2Σ state of OH in low pressure combustion flames, can be accounted for by using sufficiently large values for P_(max)χ (Sec. II). Whether or not experimental data should be interpreted in this manner must be determined by auxiliary studies. Representative absorption studies for the determination of rotational temperatures in isothermal systems have been analyzed for the P_1 branch, (0,0) band, ^2π-->^2Σ transitions of OH at 3000°K. The calculations show that erroneous interpretation of experimental results occurs if the product P_(max)χ is not small compared to unity. Sample calculations for a blackbody light source show that the customary procedure for treating experimental results will permit adequate correlation of the data by straight lines up to relatively large values for P_(max)χ. It is remarkable that the preceding statement remains true even under conditions in which emission data clearly indicate that P_(max)χ is no longer small compared to unity (Sec. III). Representative calculations to determine observable peak and total intensity ratios in emission for spectral lines with Doppler contour have been carried out for ^2Σ-->^2π transitions, (0,0) band, P_1 branch of OH at 3000°K. The calculations show that the ratios of peak and total intensities are functions of the products of maximum absorption coefficients (P_(max)) and optical density (χ) for the lines under study (Sec. IV). Quantitative calculations have been carried out of apparent rotational temperatures in systems containing nonequilibrium distributions of OH at 3000°K and at 6000°K. The calculations on the P_1 branch, ^2Σ-->^2π transitions, indicate that, in the absence of self-absorption, conventional plots showing discontinuities necessarily overestimate one and underestimate the other of the known temperatures of 3000°K and 6000°K (Sec. V). Quantitative calculations on the nature of distortions produced when an isothermal region at 3000°K is viewed through an isothermal region at 1500°K show that the presence of a non-isothermal field of view magnifies the distortion produced by self-absorption alone (Sec. VI). On the basis of the noncontroversial quantitative calculations described in Secs. II to VI for idealized systems, some speculations regarding the significance of reported flame temperature anomalies for OH are presented in Sec. VII

Spectroscopic studies of premixed laminar flames

A critical review is presented of the results obtained by spectroscopic observations on flames. The objective of the survey is to examine the status, promise, and deficiencies of combustion spectroscopy in its relation to (a) elucidation of the mechanism of combustion and (b) the solution of technical combustion problems. Since important spectroscopic studies have been carried out on low-pressure flames, a discussion of the probable effects of pressure on laminar flame propagation is also included

Approximate Emissivity Calculations for Polyatomic Molecules. I. CO_2

Approximate emissivity calculations for CO_2 have been carried out, as a function of optical density, at 300 and at 600°K. The calculations involve the assumption that the rotational lines overlap extensively. This condition appears to be satisfied at total pressures above about 1 atmos. Comparison of the values calculated from spectroscopic data with the emissivities tabulated by Hottel and his collaborators shows satisfactory agreement. The analysis presented in this manuscript emphasizes the fact that it is possible to obtain reasonable estimates for the engineering emissivity without performing extensive analytical work, provided the physical principles are understood and the needed spectroscopic data are available

Radiant energy emission from excited harmonic oscillators

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Note on the application of near-frozen flow criteria for one-dimensional nonviscous expansion through a Laval nozzle

A general criterion for near-frozen adiabatic expansion in one-dimensional nonviscous flow through a Laval nozzle has been described in a recent publication [1]. Unfortunately it appears that the discussion was so condensed that it is hardly possible to apply the results, Eq. (28a), without a few explanatory remarks