Infrared HCN Lineshapes as a Test of Galatry and Speed-Dependent Voigt Profiles

Absorption lineshapes of the ν₂ infrared band of HCN in collision with He, Ne, Ar, Kr, Xe, N₂, HCN, and CH₃Br have been considered. Observed lineshapes differ significantly from the usual Voigt profile and are characteristic of line narrowing processes. The Galatry profile fairly reproduces lineshapes observed in the low-pressure regime, but leads to unexpected nonlinear behavior of optical diffusion rates in the high-pressure regime and strongly fails with the heaviest perturbers. On the other hand, fair results are obtained for all experimental conditions by using a speed-dependent Voigt profile that includes a pressure-dependent narrowing parameter. These observations are discussed by consideration of the polarization correlation functions related to considered line profiles and of the optical and kinetic radii involved in collision processes. It is shown that observed line narrowings primarily result from the dependence of relaxation rates on molecular speeds and that diffusion processes show up with the two lighter perturbers only, He and, to a small extent, Ne. Finally, it can be claimed that, for atmospheric applications, deviations from the Voigt profile must be taken into account by a speed-dependent Galatry profile that reduces to a speed-dependent Voigt profile in most cases.     

N2- and O2-broadening coefficients and profiles for millimeter lines of N2O

For the purpose of atmospheric applications, we have measured N₂- and O₂-induced broadenings and shapes of rotational lines of N₂O in the 235-350 K temperature range, precisely the J=8←7, J=22←21, and J=23←22 lines, located near 201, 552, and 577 GHz, respectively. The analysis of experimental lineshapes shows up significant deviations from the Voigt profile, which are characteristic of line narrowing processes. In a first step, the Voigt profile was considered for the determination of pressure broadening parameters and of their temperature dependencies. Results are in good agreement with the dependence from rotational quantum number previously observed for other rotational and rovibrational lines. They are well explained by calculations based on a semiclassical formalism that includes the atom-atom Lennard-Jones potential in addition to electrostatic interactions up to hexadecapolar contributions. In a second step, observed lineshapes were analyzed by using the Galatry profile and a speed-dependent Voigt profile. The nonlinear pressure behavior observed for the diffusion rate β involved in the Galatry profile leads to rule out the possible role of velocity/speed changing collisions, and to infer that discrepancies from the Voigt profile result from the dependence of relaxation rates on molecular speeds. This interpretation is supported by the comparison of optical and kinetic radii and confirmed by theoretical calculations of relaxation rates. Finally, it can be claimed that, for the N₂O-N₂ and N₂O-O₂ systems, deviations from the Voigt profile are explained by a speed-dependent Voigt profile.     

Temperature-dependent pressure broadened line shape measurements in the ν 1+ν 3 band of acetylene using a diode laser referenced to a frequency comb

Using an extended cavity diode laser referenced to a femtosecond frequency comb, the P(11) absorption line in the ?? ₁+?? ₃ combination band of the most abundant isotopologue of pure acetylene was studied at temperatures of 296, 240, 200, 175, 165, 160, 155, and 150?K to determine pressure-dependent line shape parameters at these temperatures. The laser emission profile, the instrumental resolution, is a Lorentz function characterized by a half width at half the maximum emission (HWHM) of 8.3×10^?6?cm^?1 (or 250?kHz) for these measurements. Six collision models were tested in fitting the experimental data: Voigt, speed-dependent Voigt, Rautian?CSobel??man, Galatry, and two Rautian?CGalatry hybrid models (with and without speed-dependence). Only the speed-dependent Voigt model was able to fit the data to the experimental noise level at all temperatures and for pressures between 3 and nearly 360?torr. The variations of the speed-dependent Voigt profile line shape parameters with temperature were also characterized, and this model accurately reproduces the observations over their entire range of temperature and pressure.     

An empirical study on the importance of a speed-dependent Voigt line shape model for tropospheric water vapor profile remote sensing

We use high quality ground-based solar absorption spectra measured in close coincidence with Vaisala RS92 radiosonde in situ water vapor profiles to demonstrate that a Voigt line shape model yields systematic errors in the remotely sensed tropospheric water vapor profiles. We analyse absorption signatures of 4 H₂¹⁶O and 2 HD¹⁶O bands situated between 790 and 4710 cm⁻¹. We find that applying a speed-dependent Voigt line shape model instead of a Voigt line shape model significantly improves the agreement between the water vapor profiles obtained by the radiosondes and by infrared remote-sensing in the different bands. An optimal agreement is obtained for a Γ₂ (relaxation rate for speed-dependence) of 6-21% of Γ₀ (Voigt relaxation rate), which is consistent to the values derived from laboratory experiments. Our study suggests that further extensive laboratory investigations of line shape models are a key for improving the quality of modern water vapor remote sensing products.     

Temperature effects on the width,shift and asymmetry of 748.8 nm self-broadened neon line

The influence of temperature on the shape of the self-broadened 748.8 nm Ne line emitted from the low pressure glow discharge of neon was investigated with a Fabry-Perot interferometer. Detailed analysis showed departures of the registered line shapes from the ordinary Voigt profile. These departures were consistent with fits of the speed-dependent asymmetric Voigt profile to experimental profiles. The values of the pressure broadening, shifting and collision-time asymmetry were determined and compared with those calculated in the adiabatic approximation for the van der Waals and Lennard-Jones potentials.     

Relaxation and Lineshape of the 500.4-GHz Line of Ozone Perturbed by N(2) and O(2)

N(2)- and O(2)-broadened linewidths of the J = 34(2,32) <-- 34(1,33) transition of ozone located at 500.4 GHz have been measured at three temperatures in the 247-295 K range by using a video-type spectrometer. Besides the Voigt profile commonly used as theoretical model for millimeter-wave investigations, different other theoretical lineshapes, the speed-dependent Voigt profile, the Galatry profile, and the speed-dependent Galatry profile, have been considered to analyze the experimental spectra, to retrieve the pressure-broadening parameters, and to give an account of the pointed out line-narrowing effect. The results for O(3) perturbed by N(2) and O(2) are finally compared to calculations based on the complex semiclassical theory of Robert and Bonamy, and with previous reported values involving the same kind of transitions. Finally, it is shown that observed line narrowings result nearly exclusively from the dependence of relaxation on molecular speeds. Copyright 2000 Academic Press.     

Absolute molecular density determinations by direct referencing of a quantum cascade laser to an optical frequency comb

We propose a new approach to chemical gas analysis in the gas phase by direct referencing of a quantum cascade laser (QCL) to a near-infrared optical frequency comb. The concept was demonstrated through measurements of CO₂ molecular densities, reaching a precision of 0.2 %. Thanks to the robust phase lock of the QCL to the comb, absorption profiles could be recorded with high accuracy and repeatability by tuning the repetition rate of the comb. Such a scheme gave us the opportunity to test a variety of semiclassical line-shape models, accounting for both Dicke narrowing and speed-dependent effects. The success of the speed-dependent Nelkin–Ghatak model, with a hypergeometric dependence of the pressure broadening coefficient on the absorber speed, was demonstrated. Finally, the dependence of molecular density determinations on the choice of the line-shape model was investigated, thus demonstrating the inadequacy of the Voigt profile.     

Argon-broadening coefficients in the ν5 band of acetylene at room and low temperatures

Ar-broadening coefficients have been measured in the P- and R-branches of the ν₅ fundamental band of C₂H₂ for 30 lines at room temperature and 8 lines at −100 °C, using a tunable diode-laser spectrometer. These lines with J values ranging from 2 to 27 are located in the spectral range 665-795 cm⁻¹. The collisional widths are obtained by fitting each absorption line with three lineshape models: the Voigt profile, the Rautian profile accounting for the Dicke narrowing effect, and a general Rautian profile including the absorber speed-dependent collisional broadening. The latter model provides significantly larger broadening coefficients than the Voigt model. These coefficients are also calculated from a semiclassical theory performed by using a simple intermolecular potential with two adjustable parameters. Finally, the temperature dependence of the broadening coefficients has been determined both experimentally and theoretically.     

Measurement and computations for temperature dependences of self-broadened carbon dioxide transitions in the 30012←00001 and 30013←00001 bands

Using a Fourier transform spectrometer setup we have measured the self-broadened half width, pressure shift, and line asymmetry coefficients for transitions in the 30012←00001 and 30013←00001 vibrational bands of carbon dioxide for four different temperatures. A total of 46 pure CO₂ spectra were recorded at 0.008 and 0.009 cm⁻¹ resolution and at pressures varying from a few Torr to nearly an atmosphere. The individual spectral line profiles have been fitted by a Voigt profile and a speed-dependent Voigt profile, to which we have added dispersion profiles to account for weak line mixing. A comparison of the sets of results obtained for each band showed no vibrational dependence of the broadening coefficients. The self-broadening and self-shift coefficients are compared to semiclassical calculations based on the Robert-Bonamy formalism and were found to be in good agreement. The line asymmetry results are compared to line mixing calculations based on the Energy Corrected Sudden (ECS) and Exponential Power Gap models.     

Asymmetry and speed-dependent effects on the 748.8 nm self-broadened neon line

Using an interferometric method, detailed analysis of the self-broadened 748.8 nm Ne line shapes emitted from the glow discharge of neon was performed, where departures from the ordinary Voigt profile were observed. These departures are shown to be consistent with fits of the speed-dependent asymmetric Voigt profile to experimental profiles. It was shown that neglecting the correlation between Doppler and collisional broadening may cause errors in determined line shape parameter values. Coefficients of the pressure broadening, shift and collision-time asymmetry are determined and compared with those calculated in the adiabatic approximation for the van der Waals and Lennard-Jones potentials.     

Diode laser measurements of the first overtone HF lineshape broadened by Ar,Xe, Kr and N2

A high-resolution spectroscopy study of the HF first overtone vibrational–rotational 0–2 R(0) line profile was carried out in Ar, Xe, Kr and N₂ gas mixtures using near-IR tunable diode laser. The HF 0–2 R(0) analytical line is known as the most appropriate for laser detection of HF molecules in the atmosphere. Highly accurate collisional broadening, shift and “narrowing” coefficients were determined from the direct spectroscopic fit employing traditional Voigt, Rautian and Galatry symmetric profiles and using an asymmetric speed-dependent Voigt profile. These data make the information of modern spectroscopic databases, e.g., HITRAN2012, much more exact. A noticeable line shape asymmetry was investigated in detail. In this paper, the validity of the use of model profiles in spectroscopic fitting is severely discussed. For the first time, we draw attention to the need for physically realistic line shape models to avoid systematic errors in retrieved gas concentrations. We stress that in the case of HF, all considered model profiles serve only as ad hoc models; they may conceal the true physics of spectral line formation.     

Principle of temperature,velocity and pressure of upper atmospheric wind measurement for the Voigt profile

Using the accurate expression of the Fourier transform of the pure Voigt spectral line profile, we present the principle of the passive optical method to measure temperature, velocity, and pressure of atmospheric wind for the Voigt profile. Through discussion, from the Gaussian, Lorentzian and Voigt profiles, we find that velocity will not be affected, pressure can be derived for Lorentzian and Voigt profiles, and temperature will be affected greatly. By simulation and comparison, we find that temperature derived from the Voigt profile is greater than that from the Gaussian profile, and it is less than that from the Lorentzian profile. This discussion will be significant in accurate upper atmospheric wind measurement.     

Helium- and argon-broadening coefficients of phosphine lines in the ν2 and ν4 bands

Pressure broadening of phosphine lines by helium and argon at room temperature has been experimentally investigated by high-resolution diode-laser spectroscopy. The broadening coefficients are measured for 38 transitions of PH₃ in the ^QR branch of the ν₂ band and in the ^PP and ^RP branches of the ν₄ band. The recorded lines with J values ranging from 3 to 14 and K from 0 to 10 are located between 1062 and 1094 cm⁻¹. The retrieval of the collisional widths is carried out by fitting each spectral line with a Voigt profile, a Rautian profile and a speed-dependent Rautian profile. The latter model provides larger broadening coefficients than the Voigt model. They are also calculated on the basis of a semiclassical model involving the atom-atom Lennard-Jones potential. The theoretical results are in reasonable agreement with the experimental data and reproduce the J and K dependencies of the broadenings.     

Self- and foreign-gas-broadened lineshapes in the ν1 band of NH3

Precise N₂, O₂, H₂, Ar, He, and self-broadenings and shifts have been obtained for Q- and R-branch transitions in the ν₁ fundamental band of ammonia from simultaneous fits of low-noise, high-resolution difference-frequency laser spectra at pressures from 0.07 to 27 kPa (0.5-200 Torr). Observed lineshapes exhibit significant deviations from the conventional Voigt profile, which may be attributed to Dicke narrowing and/or speed-dependent broadening. At the higher pressures, line mixing is evident and must be included in the fits. For self-broadening, line mixing is dominated by collisional tunneling transitions, whereas for the non-polar buffers, rotational relaxation among selected K states is the primary mixing mechanism.     

N2-broadening coefficients in the ν2 and ν4 bands of PH3 at low temperature

N₂-broadening coefficients have been measured for 41 transitions of PH₃ at −100 °C in the ^QR branch of the ν₂ band and the ^PP, ^RP, and ^SP branches of the ν₄ band, using a tunable diode-laser spectrometer. The recorded lines with J values ranging from 1 to 13 and K from 0 to 10 are located between 1026 and 1093 cm⁻¹. The collisional widths are determined by fitting each spectral line with a Voigt profile, a Rautian profile, and a speed-dependent Rautian profile. The latter models provide larger broadening coefficients than the Voigt model. These coefficients have also been calculated on the basis of a semiclassical model of interacting linear molecules by considering an atom-atom Lennard-Jones potential in addition to the electrostatic contributions. By comparing broadening coefficients at room and low temperatures, the temperature dependence of these broadenings has been determined both experimentally and theoretically.     

大气廓线参数反演中基于大气可反演指数的正 则化参数选择方法

以大气可反演指数为指标, 采用Nelder-Mead单纯形法求解方法, 提出了一种卫星遥感资料反演大气廓线算法中动态的正则化参数选择方案. 同时针对四条典型区域廓线, 进行了选择试验. 从选择结果看, 不同廓线所对应的最优正则化参数变化幅度非常小, 因此在实际反演过程中, 为提高计算效率, 可近似取正则化参数为固定值. 这为利用卫星遥感资料进行大气廓线反演问题中正则化参数的选择提供了一种可借鉴的方法.     

Self-broadened CO line shapes in the v=2←0 band

Precise intensities, self-broadenings and shifts have been obtained for the ¹²C¹⁶O v=2←0 band from simultaneous fits of low-noise, high-resolution Fourier-transform spectra at pressures from 27 to 80 kPa (200-600 Torr). Observed line shapes exhibit deviations on the order of 1% from the conventional Voigt profile, primarily due to speed-dependent broadening and secondarily to line mixing. Dicke narrowing is reduced by over an order-of-magnitude from the diffusion value, presumably because of correlations between velocity- and phase-changing collisions.     

Spectroscopic lineshape study of the self-perturbed oxygen A-band

This paper reports accurate line positions, intensities, self-broadening, -shift and -line mixing coefficients for 56 rotational transitions from multispectrum fits of low noise, high-resolution Fourier-transform spectra. The measured line intensities are within the statistical spread of the previous measurements available in the literature—thus contributing to the efforts to measure the oxygen A-band intensities with an accuracy better than 1%. We determined the integrated band strength and Einstein A coefficient. Using our spectrum calibration method we could clearly show for the first time that there is a meaningful statistical discrepancy in the frequency standards used in spectroscopic studies for the oxygen A-band. We were able to explain how this discrepancy leads to two different sets of shifts reported in the literature and demonstrate the need for precise frequency-type transition wavenumber measurements of the oxygen A-band transitions. We observed deviations from the conventional Voigt profile due to speed-dependent broadening and line mixing effects. Dicke narrowing was observed on a selected group of spectra recorded at pressures between 98 and 337 Torr. The Dicke narrowed lineshapes were best modeled using a Galatry profile implemented using a fixed value for the velocity-changing collision rate. The weak line mixing coefficients were determined from fits using the speed-dependent models. Exponential Power Gap (EPG) and Energy Corrected Sudden (ECS) scaling laws were used to calculate the self-broadening and self-line mixing coefficients.     

H2-broadening coefficients in the ν2 and ν4 bands of PH3

H₂-broadening coefficients are measured for 41 transitions of PH₃ in the QR branch of the ν₂ band and the PP, RP, and PQ branches of the ν₄ band, using a tunable diode-laser spectrometer. The recorded lines with J values ranging from 2 to 16 and K from 0 to 11 are located between 995 and . The collisional widths are determined by fitting each spectral line with a Voigt profile, a Rautian profile, and a speed-dependent Rautian profile. The latter model provides larger broadening coefficients than the Voigt model. These coefficients γ₀(J,K) are found to decrease slightly on the whole as J increases and they decrease significantly for K values approaching or equal to J(J?4). The H₂-broadenings are also calculated on the basis of a semiclassical model of interacting linear molecules, using an atom-atom Lennard-Jones potential in addition to the weak electrostatic contributions. The theoretical results are in satisfactory agreement with the experimental data and reproduce the J and K dependencies of the broadenings, but the decrease observed for the QR(J,K) transitions with K=J is notably overestimated.     

星基大气探测资料信息容量研究

通过引入信息容量的概念,并借助Bayesian估计理论,给出了星载探测资料中所包含的如温度,湿度,O₃,SO₂,CH₄等大气参数的信息容量的计算方案,该方法充分考虑了仪器各通道对反演参数的敏感性、各通道的观测误差特性以及背景场的误差特性;然后利用该方法对HIRS,AMSU,AIRS,IAIS四种仪器以及三种组合所包含的大气温度、湿度的信息容量进行了计算,得到十分有价值的结果,该方法预期在星载大气探测仪器的设计、各仪器的评估与比较、探测资料的 关键词： 大气探测资料 信息容量 权函数矩阵