Line Shift Coefficients Research Articles

High-temperature line strength and line shape parameters measurements of Ar- and N2-perturbed CO2 lines near 4.18 µm in a shock tube

Line strengths and line shape parameters of Ar- and N2-perturbed CO2 R-branch transitions (82 ≤J″≤ 90) in the ν3 fundamental band were measured in a shock tube from 730 K to 2500 K and pressure below 1.13 atm using laser absorption spectroscopy (LAS). The retrieved absorption curves were fitted with the Voigt and the quadratic speed-dependent Voigt (qSDV) profiles to obtain the line strengths, broadening, and shift coefficients. Line strengths were compared to values in HITEMP, HITRAN2020, and Ames2021 databases, and the HITEMP shows the best agreement with the measured results. Ar- and N2-broadening and shift coefficients were regressed into the power law and the double power law form to study the temperature dependence of the targeted lines. The speed-dependence parameter aw was temperature-dependent. The J-dependence of the derived broadening and shift coefficients was discussed. The results of this work will aid the development of the absorption model in the far-wing region and the design of CO2 LAS sensors for high-temperature measurement.

Collisional broadening of molecular rovibronic lines

To meet burning needs of high-resolution pressure-induced line-shape parameters in the UV/visible regions for hot-temperature industrial and atmospheric applications as well as current and future space missions, phase-shift theory is examined in its historical context, tested and revisited using accurate numerical potentials and advanced trajectory models. First, a general analysis for arbitrary molecular systems is conducted in terms of the dimensionless parameter α determined by the differences of the Lennard-Jones parameters in the final and initial electronic absorber’s states. Temperature dependence, use of the power law and influence of Maxwell–Boltzmann averaging over relative velocities are addressed. Then, interaction-potential calculations are attempted for some representative molecular pairs (NO-Ar, NO-N2, OH-Ar and OH-N2) and the isotropic parts are fitted using the 12-6 Lennard-Jones form to get room and high-temperature line-broadening and line-shift coefficients which are compared to available measurements. It is shown that the phase-shift theory in its standard rectilinear-trajectory formulation provides linewidth and shift estimates accurate within 30%–40%. Attempted improvements using numerical potentials and curved trajectories lead to closer matches with measurements for some cases but also worsen the agreement for others. To ensure better theoretical predictions, introduction of correction terms to the usual phase-shift integral is suggested.

Broadening and Shift Coefficients of Water Absorption Lines Induced by Carbon Dioxide Pressure near 2.7 μm

Broadening and Shift Coefficients of Water Absorption Lines Induced by Carbon Dioxide Pressure near 2.7 μm

Nitrogen dioxide line shift coefficients induced by air pressure

Theoretical line shifts of nitrogen dioxide lines induced by air are reported at the room temperature (296 K). Calculations are performed for ∼31500 lines in the spectral range of 5700–7500 cm−1 for the bands including rotational quantum numbers up to = 87 and = 20. The data have been evaluated theoretically by a semi-empirical method which is based on the impact theory of broadening and includes the correction factors whose parameters can be determined by fitting the shift coefficients to the experimental data. Nitrogen dioxide plays an important role in the Earth’s tropospheric and stratospheric photochemistry, it is one of the most common anthropogenic substances emitted into the atmosphere. Nitrogen dioxide is involved in the production and destruction of ozone. The infra-red high resolution spectra of NO2 are the subject of intense interest during recent years. Obtained results are implemented in spectroscopic databases aimed at atmospheric applications such as HITRAN and GEISA. As to the line shift parameters, there are few papers. In this work, theoretical NO2-line shifts induced by air are reported for many lines.

Line intensity parameters, He-broadening and line shift coefficients in the 2v 2 0 and 3v 2 1 − v 2 1 bands of OCS

Using Fourier transform spectrometer, He-broadening coefficients in the and bands of carbonyl sulfide (16O12C32S) have been measured for the first time in the P- and R-branches. Measurements have been performed at room temperature (295 K) for 200 ro-vibrational lines with rotational quantum number ranging from 1 ≤ J ≤ 64, using a mono-spectrum non-linear least squares fitting of Voigt profiles. The measured values were discussed as a function of the rotational quantum number and compared to previous data. These broadening coefficients were also calculated on the basis of Robert and Bonamy's formalism using an ab-initio potential energy surface (PES). In addition, we have measured pressure shift coefficients for 92 transitions in both bands, these results were compared with those of the 2ν3 band. The line intensities in the and bands were also retrieved using the same spectra. The analysis of these intensities allows us to derive a consistent set of line intensity parameters such as vibrational transition moments, band intensities as well as Herman-Wallis (HW) coefficients.

Measurements of air-broadening parameters of water vapour transitions in the 7520–8586 cm−1 spectral region

The water vapour line broadening (γ) and shift (δ) coefficients for 319 lines of 11 vibrational bands 2ν3, 2ν2 +ν3, 3ν2+ν3, 5ν2, 6ν2, ν1+ν3, ν1+ν2+ν3, ν1+2ν2, ν1+3ν2, 2ν1, and 2ν1+ν2 from the spectral region 7520–8586 cm–1 induced by air pressure were measured with a Bruker IFS 125 spectrometer. The measurements were performed at a spectral resolution of 0.01 cm–1 and over a wide air pressure range. The calculations of the line-shift coefficients δ were performed in the framework of a semi-classical method. The measured air-broadening coefficients γ were combined with literature data for air- and N2-broadening coefficients γ measured for the lines in the 380–22,593 cm–1 spectral region. Combined experimental data for N = 4110 measured coefficients γ of 76 vibrational bands of H2O molecules were fitted to the empirical functions. The computed coefficients γ derived from the fitted parameters were statistically compared with the measurements. The vibrational dependence of the measured γ values and their compatibility is discussed.

Simulation of ν2 Raman band of methane as a function of pressure

AbstractThe in situ analysis of natural gas is one of the most promising applications of Raman spectroscopy. It is necessary to take into account the pressure effect on the spectrum of methane to improve the accuracy of this technique. This study aimed to develop and verify two methods for simulating the ν2 Raman band of methane at any spectral resolution and pressure. The first method was based on the use of the spectroscopic parameters of each single line (position, intensity, broadening, and shift coefficient). The second one was based on the use of the spectral profiles, each of which replaces a group of lines. The data required for the implementation of each method are presented in this work. A comparison of the calculated and measured spectra with a resolution of ~0.5 and ~7 cm−1 was performed. It was shown that the differences do not exceed 5% for each method in the range of 1–60 atm.

Line-shape parameters for the first rotational lines of HD in He

We report theoretical and experimental line-shape parameters for He-perturbed pure rotational HD lines that are relevant for the studies of gas giants atmospheres. Besides the usual pressure broadening and shift parameters, we also report their speed dependencies and Dicke parameters. The theoretical values, obtained from quantum dynamical calculations, are for the R(j=0-3) lines and S(j=0-2) and temperatures from 10 to 500 K. The measurements, performed using stimulated Raman spectroscopy, were done for the S(j=0-2) rotational Raman lines at 77, 195 and 298 K. We also compare the results of our calculations with pressure broadening and line shift coefficients available in the literature at 77, 195 and 300 K for the studied R lines. We demonstrate that a simple Voigt profile is insufficient to accurately model the shapes of He-perturbed HD lines at conditions relevant to gas giants atmospheres, and one should incorporate also the speed-dependent effects and velocity-changing collisions.

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

N2-collisional shift coefficients of lines in the ν3 band of methane from low to high temperatures

This paper reports collisional N2-shift coefficients of 12 lines in the ν3 band of methane measured from low to high temperature (from 123 to 598 K). The measurements were done with an improved two beams tunable diode-laser spectrometer coupled with specific absorption cells that allow to make measurements at low and high temperatures. The collisional line shifts were determined by individual fits of the experimental line shapes using the Voigt profile, as well as the Rautian-Sobel’man and the Galatry models that take into account the Dicke narrowing. The measurement procedure records simultaneously an unperturbed line of pure CH4 and the same N2-shifted transition to determine the line shift coefficient for each temperature. The temperature dependence of the line shift coefficient were determined using the linear law, the power law and the new physics based model (Double Power Law - DPL) developed by Gamache and Vispoel [Gamache and Vispoel, JQSRT, 217, 440–452, 2018]. The DPL fit of the line shift coefficient evolution with the temperature were compared to the power law and the linear law. The results show a better agreement with the DPL model.

Broadening and Shift Coefficients of H2O Absorption Lines in the 8650–9020 cm–1 Spectral Region

The broadening and shift coefficients of H2O absorption lines are compared for Ar, He, H2, and N2 buffer gases. The broadening and shift coefficients were derived from the analysis of the absorption spectra recorded with an FTIR spectrometer in the spectral region 8650–9020 cm−1 with a spectral resolution of 0.01 cm–1. Using two model line profiles (Voigt and speed-dependent Voigt profiles) the parameters of the H2O absorption lines were calculated. It is shown that the speed-dependent Voigt profile provides better agreement with experimental data.

Vibrational Dependences of Broadening and Shift Coefficients of H2O Absorption Lines Perturbed by Ne, Kr, and Xe

The dependence of the intermolecular interaction potentials on the vibrational quantum numbers of the H2O molecule is derived for the H2O–Ne, H2O–Kr, and H2O–Xe systems. The broadening γ and shift δ coefficients are calculated for seven vibrational bands ν1, ν2, ν3, 2ν2, ν1 + ν2, ν2 + ν3, and ν1 + ν2 + ν3 of the H2O molecule from the absorption region 640–9550 cm−1. An analytical formula is suggested for calculation of the broadening coefficients γ at T = 296 K. It is shown that the excitation of stretching modes of the vibrations in the H2O molecule increases the broadening coefficients. The influence of the bending vibrations on γ is insignificant.

Laser-based measurements of pressure broadening and pressure shift coefficients of combustion-relevant absorption lines in the near-infrared region

A set of high-resolution absorption spectrometers based on TDLAS was used to determine the impact of combustion-relevant gases on the pressure shift and broadening of H2O, CO2, C2H2 and CH4 absorption lines in the near-infrared spectral region. In particular, self- and foreign-broadening coefficients induced by CO2, N2, O2, air, C2H2 and CH4 were measured. The absorption lines under investigation are suitable to measure the respective species in typical combustion environments via laser absorption spectroscopy. Additionally, species-dependent self- and foreign-induced pressure shift coefficients were measured and compared to the literature. The experiments were performed in two specifically designed absorption cells over a wide pressure range from 5 to 180 kPa. Different sources of uncertainty were identified and quantified to achieve relative measurement uncertainties of 0.7–1.5% for broadening coefficients and 0.6–1.6% for pressure shift coefficients.

A new fully quantum-mechanical method used to calculate the collisional broadening coefficients and shift coefficients of Rb D1 lines perturbed by noble gases He and Ar**Project supported by the National Natural Science Foundation of China (Grants Nos. 11405077 and 11575073).

In this work, a new full quantum method is proposed to calculate the broadening and shift coefficients of the D1 line in neutral collision. Based on the variable phase approach and Baranger theory, this method calculates the scattering phase shift instead of scattering matrix elements in order to simplify the calculation. As an illustration, this method is used to calculate the broadening and shift coefficients of the absorption lines of alkali metal atom Rb, as it collides with buffer gas He and Ar, in a temperature range from 150 K to 800 K. With a comparison with other calculations and experiment measurements, the reasonable agreements in all cases demonstrate the validity and simplicity of this method.

Effective potentials for H2O-He and H2O-Ar systems. Isotropic induction-dispersion potentials

The vibrational and rotational dependence of the effective isotropic interaction potential of H2O–He and H2O–Ar systems, taken in the form of Lennard-Jones 6–12 potential has been analyzed. The analysis is based on the experimental line broadening (γ) and line shift (δ) coefficients obtained for different vibrational bands of H2O molecule perturbed by He and Ar. The first and second derivatives of the function C (1)(q) for the long-range part of the induction-dispersion potential with respect to the dimensionless normal coordinates q were calculated using literature information for the dipole moment and mean polarizability functions μ(q) and α(q), respectively. These derivatives have been used in the calculations of the quantities which determine the vibrational and rotational dependence of the long-range part of the effective isotropic potential. The optimal set of the derivatives for the function C (1)(q) is proposed. The comparison with the experimental data has been performed.

Line positions, pressure broadening and shift coefficients for the second overtone transitions of carbon monoxide in argon

Absolute positions and spectral line-shape parameters of carbon monoxide 0→3 band, P branch transitions are reported. The speed-dependent effects and the influence of velocity-changing collisions were taken into account in the fitted line-shape models. For the first time the values of pressure shift coefficients of CO in argon for this band were determined. The measurements were made with the Pound–Drever–Hall-locked frequency-stabilized cavity ring-down spectrometer, with the frequency axis linked through an optical frequency comb to the UTC(AOS) frequency reference based on a hydrogen maser. Achieved uncertainties of line positions are between 70kHz and 420kHz.

Fourier Transform Spectroscopy of two trace gases namely Methane and Carbon monoxide for planetary and atmospheric research application

Two atmospheric trace gases, namely methane and carbon monoxide have been considered in this study. Fourier transform absorption spectra of the 2–0 band of 12C16O mixed with CO2 have been recorded at total pressures from 156 to 1212 hPa and at 4 different temperatures between 240 K and 283 K. CO2 pressure-induced line broadening and line shift coefficients, and the associated temperature dependence have been measured in an multi-spectrum non-linear least squares analysis using Voigt profiles with an asymmetric profile due to line mixing. The measured CO2-broadening and CO2-shift parameters were compared with theoretical values, calculated by collaborators. In addition, the CO2-broadening and shift coefficients have been calculated for individual temperatures using the Exponential Power Gap (EPG) semi-empirical method. We also discuss the retrieved line shape parameters for Methane transitions in the spectral range known as the Methane Octad. We used high resolution spectra of pure methane and of dilute mixtures of methane in dry air, recorded with high signal to noise ratio at temperatures between 148 K and room temperature using the Bruker IFS 125 HR Fourier transform spectrometer (FTS) at the Jet Propulsion Laboratory, Pasadena, California. Theoretical calculations for line parameters have been performed and the results are compared with the previously published values and with the line parameters available in the GEISA2015 [1] and HITRAN2012 [2] databases.

CO2 pressure broadening and shift coefficients for the 2–0 band of 12C16O

Fourier transform absorption spectra of the 2–0 band of 12C16O mixed with CO2 have been recorded at total pressures from 156 to 1212hPa and at 4 different temperatures between 240K and 283K. CO2 pressure-induced line broadening and line shift coefficients, and the temperature dependence of the former have been measured including line mixing using a multi-spectrum non-linear least squares fitting technique. Different line shape models have been considered to take into account the Dicke narrowing or speed dependence effects. Measured line-shape parameters were compared with theoretical values, calculated for individual temperatures using a semi-empirical method and the Exponential Power Gap (EPG) law.

A new approach to spectral line shapes of the weak oxygen transitions for atmospheric applications

We propose to construct a new database of O2 molecular spectral lines for atmospheric application, consistent with recent IUPAC recommendation [Tennyson et al. Pure Appl Chem 2014;86:1931] going beyond Voigt profile by incorporation of the speed dependence of collisional broadening and shifting. For this purpose we collected the laboratory data for the self-perturbed oxygen B-band transitions. Line shapes were measured at low pressures by the Pound–Drever–Hall-locked frequency-stabilized cavity ring-down spectrometer linked to the optical frequency comb. Data were analyzed by means of the quadratic speed-dependent Voigt profile. The absolute transition frequencies are determined with accuracy even as good as 150kHz. Line intensities, pressure width and shift coefficients and the speed-dependent parameters are determined with subpercent accuracy.

Measurements of N2-broadening and pressure-shift coefficients in the ν3-band of 12CH4 using a cw-OPO

We have measured the nitrogen-collision-induced line broadening and line shift coefficients of three singlet lines – P(1), R(0) and R(1) – belonging to the ν3 band of methane (12CH4) at 3.29–3.32μm using direct laser absorption spectroscopy by means of a continuous-wave mid-IR optical parametric oscillator. Owing to the well-isolated features of the singlet lines, the lineshapes were modeled with a simple Voigt profile in order to retrieve the line parameter coefficients. The values of the N2-broadening and pressure-shift coefficients agree fairly well with the previously published ones that use either Fourier-transform or mid-infrared difference-frequency spectrometers along with more complex analytic spectroscopic models.