Self-broadening Coefficients Research Articles

H2O Collisional Broadening Coefficients at 1.37 µm and Their Temperature Dependence: A Metrology Approach

We report self- and air collisional broadening coefficients for the H2O line at 7299.43 cm−1 and corresponding temperature coefficients for a temperature range spanning 293–573 K. New laser spectroscopic setups specifically designed for this purpose have been developed and are described. The line parameters reported here are in good agreement with those values reported in the HITRAN 2020 database, but the uncertainties have been reduced by factors of about 4, 1.3 and 4.4 for the self-broadening coefficient, air broadening coefficient and the temperature exponent of air broadening, respectively. Further, we combined our measurement approach with metrological data quality objectives, addressing the traceability of the results to the international system of units (SI) and evaluated the uncertainties following the guide to the expression of uncertainty in measurement (GUM).

Calculation and Analysis of Self-Broadening Coefficients of Water Vapor Lines for the Spectrum Range of 0.7–14 000.0 cm–1

Calculation and Analysis of Self-Broadening Coefficients of Water Vapor Lines for the Spectrum Range of 0.7–14 000.0 cm–1

Ammonia line strengths and N2-, O2-, Ar-, He-, and self-broadening coefficients in the v2 band near 10.4 µm

Scanning-wavelength laser absorption measurements were carried out to determine the line strengths and broadening coefficients due to collisions of N2, O2, Ar, He, and NH3 for 12 ammonia transitions in the Q-branch of the v2 fundamental band near 10.4 µm. The measurements were conducted at 296 K using a high-resolution quantum cascade laser and span the frequency range of 957.5–963.0 cm−1. The absorption features were fitted with a Voigt profile to obtain the spectroscopic parameters. The temperature-dependence of the Ar-broadening coefficients for two transitions, suitable for high-temperature NH3 detection, were measured using a shock tube for the temperature range of 921–1767 K. The reported spectroscopic parameters are useful for developing NH3 detection sensors, especially for high-temperature applications involving chemical reactions.

Study on dual-optical paths for simultaneous measurement method of water vapor absorption spectrum in 1 μm band

Based on the gas multi-pass absorption cell with dual-optical paths (long optical path: 72.46 m; short optical path: 36.23 m), a measurement method of simultaneously detecting water vapor absorption spectra is advanced. Combining with a narrow line-width external cavity diode laser and a high-precision Fabry-Perot etalon, a high-resolution simultaneous measurement device with dual-optical paths for water vapor absorption spectra in 1 μm band is developed. Since the external cavity diode laser has excellent polarization characteristics which could be combined with a half-wave plate and a polarization beam splitter to implement the laser transmissions in dual-optical paths simultaneously. Both the multi-pass absorption cell and the Fabry-Perot etalon in the measurement device have pressure and temperature control units, which are utilized for achieving ambient stability. The free spectral range of Fabry-Perot etalon is accurately measured by the method of optical comb frequency. Corresponding free spectral range with a deviation of only 0.02 % from the theoretical value is obtained to be a value of 749.52 MHz, and the influence of temperature on the frequency shift of etalon is less than 1 % of the measured value. The stability of the pressure and the temperature in the dual-optical path gas multi-pass absorption cell in the system are evaluated in detail, and the calculated relative errors are not more than 0.03 % and 0.02 %, respectively. At a temperature of 300 K, the system is used to measure the absorption spectra of water vapor at 9152.53 cm<sup>–1</sup> from 400 Pa to 2000 Pa on dual-optical paths, then the integrated absorbance and Lorentzian line-width of water vapor for long optical path and short optical path are inverted by fitting absorption spectra with Voigt profile respectively. The absorption line intensities and self-broadening coefficients are acquired by performing linear fitting to the integrated absorbance and Lorentzian line-width under different pressures. And the relative deviations of the average values of the dual-optical path absorption line intensities (converted to the reference temperature of 296 K) and the self-broadening coefficients and the corresponding data of the HITRAN2016 database are 0.78 % and 3.8 %, respectively. Consequently, the feasibility of the dual-optical path simultaneous measurement method and the reliability of the measurement device are demonstrated by the results.

Nitrogen and Oxygen Self-Broadening and Shift Coefficients of Rotational-Vibrational Raman Band in 1–50 ATM Range

Nitrogen and Oxygen Self-Broadening and Shift Coefficients of Rotational-Vibrational Raman Band in 1–50 ATM Range

Nonpolynomial representation of N2-, air-, and self-broadening coefficients of ozone lines

Nonpolynomial representation of N2-, air-, and self-broadening coefficients of ozone lines

Measurements of pressure broadening of N2 in the anisotropic tensor component of spontaneous Raman spectra

Spontaneous Raman scattering from nitrogen is well-suited for temperature measurements in combustion experiments, especially at high pressure which increases the Raman signal because of the higher density in the measurement volume. In this work we investigate high density effects on the anisotropic tensor component of ro-vibrational spontaneous Raman scattering, which must be understood to obtain accurate thermometry in high pressure gases using high-fidelity Raman simulations. We measure the collision broadening for the anisotropic component of spontaneous Raman scattering from room temperature nitrogen over the pressure range 10–70 atm for three gas compositions: pure nitrogen, air, and nitrogen in argon. Line broadening coefficients inferred from these measurements were found to be 14 ± 5% larger than the corresponding broadening coefficients of the isotropic Q branch. Air broadening coefficients were found to be very similar and about 2.5% smaller than nitrogen self-broadening coefficients. Argon broadening coefficients were 25% smaller at rotational quantum number 7 and about 50% smaller at rotational quantum number 21. Additionally, we found that our unmixed line model for the O and S branches gave good fits for all pressures, which indicates that line mixing effects are not significant in the O and S branches over this range of pressures. Using indirect experimental evidence we infer that line mixing effects in the anisotropic component of the Q branch were below the threshold set by our experimental spectral resolution at pressures up to 70 atm at room temperature. Assuming that the anisotropic Q branch lines mix like the isotropic lines results in a small systematic error in the inferred temperature at flame temperatures, with the error increasing slowly with pressure. The bias can be easily removed by modeling the anisotropic spectrum separately from the isotropic spectrum. Line mixing effects should be included in the model of the isotropic part of the Raman spectrum, but can probably be neglected in the anisotropic part of the spontaneous Raman spectrum of N 2 for pressures below 400 atm at flame temperatures.

Measurements of Line Intensities and Self-broadening Coefficients in the ν2 Band of CH3I

The line intensities and pressure broadening coefficients for transitions in the three branches of the ν2 parallel band of CH3I are measured for the first time for about 1317 lines with rotational quantum numbers 2 ≤ J ≤ 70 and 0 ≤ K ≤ 13 using a mono-spectrum fitting technique utilizing a Voigt profile. Five spectra have been recorded at room temperature (T = 297.6 K) with a high resolution Fourier transform spectrometer at pressures between 1.15 and 9.98 mbar. The measured intensities were used to derive the transition dipole moment squared for each line, the band intensity as well as the Herman–Wallis coefficients. These parameters were used to predict the values of line intensities. The band intensity was compared with previous works performed at medium resolution. The rotational dependencies of the self-broadening coefficients have been clearly observed and modeled using an empirical model. The average accuracies were estimated to be around 5 % for line intensities and self-broadening coefficients.The whole set of results is given as supplementary material for a possible use in atmospheric and industrial applications.

Influence of Uncertainty of Probabilities of Spontaneous Emission on the Temperature Behavior of the Collisional Self-Broadening Coefficients of Spectral Lines of CO2 Molecules

The influence of deviation of the values of spontaneous emission probability A on the temperature behavior of collisional self-broadening coefficients γ(T) of spectral lines of CO2 molecules has been analyzed for solution of the inverse problem of simultaneous determination of A and γ from an array of absorption coefficients. Investigations have been carried out for two cases: (i) the calculations are performed using A = 0.2022 s–1 (HITRAN2012); (ii) the A values are obtained via minimization of the sum of weighted squared deviations of the absorption coefficients. It is established for the two calculation versions that, when measuring the absorption coefficients with an error of no more than 0.05αmin, the deviation of the functions γ(T) does not exceed 5% in the temperature range of 300–700 K. No causal relationship is observed between parameters γ and A. The least-squares method makes it possible to correctly calculate the temperature dependences of the collisional self-broadening coefficients of CO2 lines at simultaneous determination of parameters γ(T) and A.

Self-broadening coefficients in the ν2 +2ν3 band of 13CH4 at temperatures from 296 K to 200 K

The 13CH4 absorption spectra in the range between 7400 and 7600 cm−1 have been recorded at 4 temperatures from 296 K to 200 K using a Fourier transform spectrometer at pressures from 1 to 300 hPa, and at a 0.01 and 0.03 cm−1 spectral resolution. A 60 cm multipath cell with a path length of 1920 cm and a 220 long cm low temperature cell were used, which provided a threshold sensitivity to absorption of the order of 10−6 cm−1. The parameters of the Hartmann-Tran and Voigt lineshapes (line positions, intensities, self-broadening coefficients, self-shift coefficients and temperature dependences of the half width coefficients) were determined for the strongest transitions of the 13CH4 ν2 +2ν3 band.

Optical feedback laser absorption spectroscopy of N2O at 2 µm

We present high-accuracy measurements of the spectroscopic parameters of eight nitrous oxide transitions, mainly belonging to the P branch of the 3ν1+2ν2 vibrational band, in the spectral region around 4982 cm−1. We acquired absorption spectra in pure N2O samples, at room-temperature, by means of a diode laser based spectrometer in which the laser emission width was effectively narrowed by exploiting the optical feedback from a V-shaped high-finesse cavity. The spectrometer was assisted by a self-referenced optical frequency comb synthesizer for frequency calibration purposes. Light absorption from N2O molecules occurred inside a multiple reflections cell, which was placed on the transmission from the cavity. The successful application of a global fitting approach to a manifold of spectra, involving the symmetric uncorrelated version of quadratic speed-dependent hard collision profile, allowed us to determine line intensities with an overall relative uncertainty of 0.38%. We found a satisfactory agreement with data provided by the HITRAN and NOSD-1000 databases. Self-broadening coefficients, speed dependence components of the collisional line broadening, and Dicke narrowing parameters were also determined.

Fourier transform CO spectra near 1.6 μm

The absorption spectra of carbon monoxide have been recorded in the 6000–6450 cm−1 wavenumber regions using the Bruker IFS 125 HR Fourier transform spectrometer and a 30 m multipass cell with the White-type optical system. The spectra were recorded at spectral resolution of 0.008–0.012 cm−1, path length up to 1058 m, and at pressure range from 30 to 320 mbar. The temperature was about 301 K. The lines of the 3-0 bands of six isotopologues 12C16O, 13C16O, 12C18O, 12C17O, 13C18O, 13C17O and the lines of the hot 4-1 band of 12C16O were assigned in the spectra. The line intensities and the self-broadening coefficients were measured. In the case of the principal isotopologue the line intensities were determined for the lines with the angular momentum quantum number J up to 41. The effective dipole moment parameters describing the line intensities of the observed bands were fitted to the observed values of the line intensities. The uncertainty of the line intensity measurements for the strong unsaturated and unblended lines of the principal isotopologue varies between 2% and 2.5%. The comparison of our measured line intensities to those of other authors and of the HITRAN2016 database is given.

Коэффициенты самоуширения и сдвига колебательно-вращательных линий КР азота и кислорода в диапазоне давлений 1-50 атм

Коэффициенты самоуширения и сдвига колебательно-вращательных линий КР азота и кислорода в диапазоне давлений 1-50 атм

Влияние неопределенности значений вероятностей спонтанного излучения на температурное поведение коэффициентов ударного самоуширения спектральных линий молекул CO-=SUB=-2-=/SUB=-

The influence of the deviation of the spontaneous radiation probability of the spectral lines of CO2 A on the temperature dependence of the collisional self-broadened coefficients γ in solving the inverse problem of joint determination of A and γ from the array of absorption coefficients is studied. The study was carried out for two cases: 1) A=0.2022 s-1 (HITRAN2012); 2) the values of A were obtained by minimizing the sum of weighted squares of the absorption coefficients differences. It was found that in the temperature range of 300-700 K, when the absorption coefficients are measured with accuracy 0.05∙αmin, the deviation of the functions γ(T) does not exceed 5%. There is no causal relationship between the parameters γ and A. The method of least squares allows us to correctly calculate the temperature dependences of the collisional self-broadened coefficients of the CO2 lines γ(T).

Temperature dependence of CH3I self-broadening coefficients in the ν6 fundamental

Temperature dependence of methyl iodide self-broadening coefficients in the fundamental ν6 band is evaluated theoretically by the use of a semi-classical and a semi-empirical approaches in the range 200–400 K recommended for HITRAN. In the absence of not-room-temperature measurements, comparisons are performed solely between line-width sets computed by the two methods at some fixed temperatures. Traditional temperature exponents as well as parameters of the recently suggested double power law [JQSRT 2018;217:440-52] (going beyond the considered temperature range) are determined for (J, K)-lines with 0 ≤ J ≤ 70, K ≤ 20 requested by spectroscopic databases. Because of the negligible vibrational dependence, these data can be safely used for other perpendicular and parallel bands studied in atmospheric applications.

Line intensities and self-broadening coefficients of methyl chloride in the 10 µm region

We performed the first systematic measurements of line intensities and pressure broadening coefficients of ro-vibrational absorption transitions of the ν6 perpendicular band of CH335Cl and CH337Cl isotopologues. The spectra were recorded in the spectral region between 920 and 1130 cm−1 with a high-resolution Fourier transform spectrometer. A multi-pressure fitting technique was used to fit a series of seven spectra at pressures of CH3Cl ranging from 1.02 to 10.24 mbar to derive these parameters for about 2132 transitions with 1 ≤ J ≤ 55 and 0 ≤ K ≤ 12. The line intensities were discussed as a function of the rotational quantum numbers, and were used to derive the transition dipole moments squared for each line. The analysis of these moments allows us to derive a consistent set of line intensity parameters such as vibrational transition moments, band intensity as well as Herman-Wallis coefficients. The results were found to be in satisfactory agreement with databases and with low resolution measurements of band intensity.The rotational dependencies of the self-broadening coefficients have been clearly observed and modeled using an empirical polynomial law. The average accuracies have been estimated to be around 4 and 5% for line intensities and self-broadening coefficients respectively.

Absorption spectroscopy of ethylene near 1.62 µm at high temperatures

We report the measured line positions, line intensities, self-broadening coefficients and its temperature exponent n of C2H4 for more than 50 lines in the frequency range 6167.39 to 6177.71 cm−1. These spectroscopic parameters were determined by multi-line fitting using the Voigt profile of absorption spectra measured with a distributed-feedback (DFB) tunable diode laser in a well-controlled heated static absorption cell in a temperature range of 296–600 K. The key factors influencing the uncertainties in the determination of the line intensities and self-broadening coefficients were analyzed respectively. To the best of our knowledge, this is the first study that measures the spectrum of C2H4 near 1.62 µm and the line parameters at elevated temperature.

Absorption lines measurements of carbon disulfide at 4.6 μm with quantum cascade laser absorption spectroscopy

We report measured line intensities and air- and self-broadening coefficients for fifty-one carbon disulfide transitions in the ν1 + ν3 band near 4.6 μm. This spectral region was chosen due to the strong carbon disulfide absorption strength and in the range of the mid-infrared atmospheric window for laser-based sensing applications. Spectroscopic parameters were determined by spectra measuring with quantum cascade laser direct absorption spectroscopy and multi-line fitting with Voigt lineshape. These measured results would facilitate the development of calibrated-free mid-infrared carbon disulfide sensors.

Room temperature line parameters of the self- and air-broadened fundamental vibrational transition of carbon monoxide: experimental results and calculations

We have analyzed 10 room temperature spectra of the fundamental band of CO and CO-air using the Voigt, speed-dependent Voigt, speed-dependent Rautian line shape models. Line positions, intensities, air- and self-broadening coefficients, pressure induced air- and self-shift coefficients, and line-mixing parameters have been retrieved. The CO- and N2-broadened carbon monoxide half width coefficients have been calculated using a potential energy surface based on Tipping-Herman intermolecular interaction potential and taking the electrostatic interactions into account.

Extended analysis of the ν12 band of 12C2H4 for astrophysical applications: Line strengths, widths, and shifts

The high-resolution infrared spectra of 12C2H4 were analyzed in the region of 1360 – 1530 cm−1, where the strong ν12 band is located. 998 line strengths (1491 transitions) were determined from the fit of their line shapes with a Hartmann–Tran profile (Jmax=48 and Kamax=17) which is about two times more than in the preceding studies. These data were used in the fit of the effective dipole moment parameters and six such parameters were obtained which reproduce the strengths of the 998 initial lines (1491 transitions) with the drms=2.31%. Self–broadening and self-shift coefficients were determined from the multi–spectrum analysis for sets of lines (JKa=Ka′Kc)←(J′Ka′Kc′),Ka′=0,1,2,3,4,5 (in general, 253 lines for determination of self-broadening coefficients and 225 lines for determination of self-shift coefficients). The line list of 19186 transitions is documented.