Line parameter measurements and calculations of CO broadened by nitrogen at elevated temperatures

Measurements of the line strengths and collisional broadening widths of CO in a N₂ atmosphere were made from 300 to 600 K. The lines studied were the P(2), P(3), P(7), P(12), P(18), and P(22) lines of the fundamental band at 2100 cm^?1. The absorption spectra were parametrically fit to a Voigt lineshape model. The band strength was determined to be 250±8 cm^?2atm^?1. The broadening results are compared to Anderson-Tsao-Curnutte calculations and to other experimental studies. The possibility of using an equation of the form $\text{γ(T)=γ(T}{}_0\text{(}\text{T}{}_0\text{T}\text{)}{}^{\mathrm{n}}$ to extrapolate the temperature dependence of the half-widths to flame temperatures is discussed.     

Line parameter measurements and calculations of CO broadened by H2O and CO2 at elevated temperatures

Measurements of collisional broadening of four fundamental CO lines in atmospheres of CO₂ and H₂O at 300–600 K were made. The Voigt line-shape model was fitted parametrically to the absorption spectra line-shapes. The results are compared with other experimental studies and with theoretical calculations for CO₂ broadening. Absorption spectra of the exhaust gases of a flat flame were recorded and analyzed to yield CO concentration, temperature, and line half-widths. The flame spectra half-widths were compared with extrapolations of lower temperature data using the simple power law approximation $\text{γ(T)=γ(T}{}_0\text{) (}\text{T}{}_0\text{T}\text{)}{}^{\mathrm{n}}$. The utility of this approximation in the development of combustion diagnostic techniques is discussed.     

Thermal infrared lines of methane broadened by nitrogen at low temperatures

Measurements of spectral transmittance in the v₄-fundamental band of ¹²CH₄ have been performed at low temperatures using a Fourier transform spectrometer with apodized spectral resolution of 0.06 cm^-1. With applications to lines formed in the atmospheres of Titan and Earth in mind, N₂ has been used as the broadening gas. Comparisons of observed and computed spectral transmittances on a line-by-line basis have yielded line strengths, N₂-broadened half-widths and their variation with temperature. Best agreement between measured and computed spectra was obtained when the absolute intensity of the band was taken as 128 cm^-2-atm^-1 at 296 K. Line widths were found to vary as Tⁿ with n = -1.0 for lines of the F-species and 0.63 for the A-species. Our measured line widths are considerably larger than those used in the AFGL compilation.     

Diode laser measurements of CO line widths at planetary atmospheric temperatures

Hydrogen-broadened half-widths and nitrogen-broadened half-widths of eight lines between P(1) and P(15) in the CO fundamental have been measured at several temperatures between 94 and 298 K using a tunable diode laser spectrometer and the sweep integration technique.     

Measurement of line widths of CO of planetary interest at low temperatures

Self-broadened, air-broadened and CO₂-broadened half-widths of lines R(0) through R(0) in the CO fundamental have been measured at 100°K (self-broadening only), 200°K, 250°K and 300°K using the Ladenburg-Reiche curve-of-growth. The relation $\text{γ}{}^{\mathrm{°}}{}_{\mathrm{m}}\text{(T)}\text{γ}{}^{\mathrm{°}}{}_{\mathrm{m}}\text{(300°K)}\text{=(}\text{300}\text{T}\text{)}{}^{0.75}$, which we found previously for the nitrogen-broadened half-widths of R(0), R(8) and R(16), is shown to be valid for all of the line widths measured in the present study.     

Simplified models for the temperature dependence of linewidths at elevated temperatures and applications to CO broadened by Ar and N2

The broadening coefficients for i.r. lines of CO perturbed by Ar are calculated in the temperature range 300–3500 K using the formalism previously developed by two of us (D.R. and J.B.). The results are compared with high-resolution spectroscopic measurements of shock-heated CO-Ar gas mixtures. A simplified model is proposed to describe the temperature dependence of the linewidths. The resulting model is applied to CO broadened by N₂ and the results are critically discussed.     

Measurements of the CO first overtone bandstrength at elevated temperatures

The spectrally resolved emission from the CO first overtone vibration-rotation band has been studied over the temperature range of 1100-2600 K in a shock-tube experiment. First overtone bandstrengths have been deduced from the data. These compare favorably with theoretical expectations.     

Half-width calculations for CO lines broadened by CO2

Half-widths of CO lines, in the fundamental and first overtone bands, broadened by CO₂ have been computed using the Anderson-Tsao-Curnutte theory. Comparison with the high-resolution measurements of Varanasi at 295°K shows excellent prediction of line widths by the theory. Comparison is also made between calculations including dipole-quadrupole and quadrupole-quadrupole interactions with those taking only the dominant quadrupole-quadrupole forces into account. Line widthd at 295°K range from 0.126417 cm^-1 atm^-1 fom m = 1 to 0.04397 cm^-1atm^-1 for m = 32, which corresponds to the asymptonic kinetic-theory value. Half-width computations are also presented at 200°K and 250°K appropriate for Martian and Venusian atmospheres, respectively.     

Air-broadened line widths of methane at atmospheric temperatures

Air-broadened half-widths of lines R(0), R(1) and R(2) in the ν₃-fundamental of ¹²CH₄ have been measured at 200°K, 250°K and 300°K.     

Strengths and widths of the pure rotational lines of CO

The strengths and widths of several lines in the pure rotational band of CO have been measured by asymmetric Fourier techniques. The strengths give a permanent dipole moment of 0.112 D, in good agreement with the micro-wave value, and show conclusively that the sign of the Herman-Wallis parameter, θ, is negative. The widths are in good agreement with the theoretical values of Benedict and Herman and do not show the anomalous J dependence recently reported by Dowling.     

R-branch head of the ν3 band of CO2 at elevated temperatures

The R-branch head of the 00⁰1 ← 00⁰0 band of ¹²C¹⁶O₂ has been recorded with Doppler-limited resolution using a tunable laser difference-frequency spectrometer. J values to 140 were measured at temperatures to 985 K. The data have been combined with extremely precise transition frequencies for 0 ≤ J ≤ 76 measured with a Fourier transform interferometer to obtain an improved set of spectral constants for this ν₃ band of CO₂.     

Measurements of nitrogen-broadened line widths of acetylene at low temperatures

Spectral transmittance measurements have been performed on N₂-broadened lines of C₂H₂ in the 7.53 μm region at 153 and 200 K with a spectral resolution of 0.06 cm^-1. The line widths have been determined as functions of temperature and rotational quantum number using line-by-line comparison of theoretical and experimental values of spectral transmittance.     

Pressure broadened line widths of BrCN in the microwave region

The line widths of cyanogen bromide (BrCN) have been measured at room temperature (305 K) by using a double modulation microwave spectrograph. The self-broadening of two quadrupole hyperfine lines of the transition J = 3 → 4 has been measured. The foreign gas broadening by OCS, CO₂, N₂, CH₃CN, CH₃I, HCHO and CH₃CHO molecules has been measured only for the intense line at 32·957 GHz. These measured line widths have been compared with the calculated line widths using Anderson [6] as well as Murphy and Boggs [8] theories of pressure broadening.     

Intensities and pressure-broadened widths of CO2 R-branch lines at 15 μm from tunable laser measurements

Intensities and half-widths of individual lines, over the temperature range 200–325°K in the 15 μm bands of ¹²C¹⁶O₂, have been determined with a tunable diode laser spectrometer. Measurements were made on pure CO₂ and on dilute CO₂-in-N₂ mixtures on the R-branches of the 01¹0-00⁰0 and 02²0-01¹0 transitions. Intensities are approximately equal to those listed in the AFGL compilation. The pressure-broadened half-widths follow the general relationship $\text{b}{}_{\mathrm{L}}{}^0\text{(T) = b}{}_{\mathrm{L}}{}^0\text{(T}{}_0\text{) [}\text{T}{}_0\text{T}\text{]}{}^{\mathrm{n}}$ where n varies considerably from line to line but is always greater than $\text{1}\text{2}$.     

Infrared-optical characteristics of ceramics at elevated temperatures

In this work the infrared-optical properties of ceramic samples at ambient and elevated temperatures are presented. The aim of this work is the determination and interpretation of the spectral transmittance, reflectance and emittance of three oxide ceramic samples (MgO, Al₂O₃/ZrO₂, TiO₂/Y₂O₃) and one carbide ceramic sample (SiC) as a function of the temperature from 300 K up to 1100 K. The semi-transparency of the ceramics in the near infrared region has to be considered when performing the measurements and evaluating the data.The experimentally derived spectra are compared with the values derived from theoretical calculations. The complex dielectric function of a ceramic can be deduced from the Lorentz oscillator model. The complex refractive index is correlated with the complex dielectric function by the Maxwell relation. Scattering effects can be described by radiative transfer models. Finally the infrared-optical properties transmittance, reflectance and emittance depend on the complex refractive index and the morphology of the ceramic sample.Of special interest is the Christiansen wavelength as well as the location of the free running frequencies of the longitudinal and transversal optical oscillations. Usually the ceramic is highly reflecting between the free running frequencies of the longitudinal and transversal optical oscillations whereas at the Christiansen wavelength the reflectance vanishes which leads to an emittance of one for an optically thick sample at the Christiansen wavelength. Due to the known emittance it is possible to use the Christiansen wavelength for determining the temperature of the investigated sample.Finally the obtained infrared-optical spectra are presented and their temperature dependencies are discussed which are mainly due to phonon excitations. Additionally it has been shown that for example the location of the Christiansen wavelength can be influenced by varying the composition of the ceramic.     

Simultaneous detection of CO and CO2 at elevated temperatures using tunable diode laser absorption spectroscopy near 1570 nm

Simultaneous measurements of CO and CO₂ at elevated temperatures are demonstrated using a single semiconductor distributed-feedback (DFB) laser near 1570 nm. Wavelength modulation spectroscopy with second-harmonic detection is used to improve the detection sensitivity and accuracy. A proper line pair near 6368.086 and 6368.330 cm^?1 is selected using some line-selection criterions for the target temperature range of 300–1000 K. Normalization of the 2f signal with the 1f signal magnitude is used to remove the need for calibration and correct for transmission variation due to beam steering, mechanical misalignments, soot, and windows fouling. The CO and CO₂ concentrations measurements are within 2.21% and 2.55% of the expected values over the tested temperature range of 300–1000 K. The minimum detectable concentrations of CO and CO₂ at 1000 K are 80 ppm m and 153 ppm m, respectively.