水汽分子对CO_2谱线加宽的影响

报道了以高分辨力连续可调谐中红外差频激光为探测光源,结合可调长光程怀特池,利用直接吸收的方法探测了CO2的10011←10002带R支以及部分P支在室温下的水汽加宽吸收光谱。在2422cm-1到2457cm-1范围内共有26条吸收谱线被探测到,采用Voigt线型对吸收谱线进行拟合,得到了CO2光谱的水汽加宽系数,结果显示CO2的水汽加宽系数平均比干燥空气的加宽系数大52%。利用实验测得的CO2的水汽加宽系数与HITRAN04数据库中CO2谱线的线位置、线强和干燥的空气加宽系数进行比较,分析了在实际大气中(海平面,10km光程)不存在水汽和存在水汽(含有2.0kPa水汽)时该波段CO2的大气透过率,结果表明潮湿空气与干燥空气之间的最大透过率差约为0.5‰。     

Self-, N2- and O2-broadening coefficients for the CO2 transitions near-IR measured by a diode laser photoacoustic spectrometer

Using a high-resolution tunable diode laser photoacoustic spectrometer, self-, N₂ and O₂ pressure broadening coefficients for the first 11 transitions of ¹²C¹⁶O₂ in the R branch of the (30012) ← (00001) overtone band at the 6348 cm⁻¹ have been revisited at room temperature (∼298 K). Air-broadening parameters have also been calculated from the N₂ and O₂ measurements. The dependence of the broadening on rotational quantum number m is discussed. The recorded lineshapes are fitted with standard Voigt line profiles in order to determine the collisional broadening coefficients of carbon dioxide transitions. The results are compared to our previous measurements and to the values reported in the HITRAN04 database and by other research group with a different spectroscopic technique.     

Pressure-induced line broadening for the (30012)←(00001) band of CO2 measured with tunable diode laser photoacoustic spectroscopy

Pressure-induced foreign-broadening lineshape parameters of the carbon dioxide rovibrational transitions belonging to the (30012)←(00001) overtone band near the 1.573 μm wavelength region are measured by using a tunable diode laser photoacoustic spectrometer. The spectroscopic analysis has concerned the first 11 lines of the R branch. For these lines, the air- and Ar-broadening coefficients are measured at room temperature (∼298 K). The measured broadening coefficients of all the transitions of ¹²C¹⁶O₂ are compared with those given in the HITRAN04 database and former measurements with a different spectroscopic method. Agreements and discrepancies are underlined and briefly discussed. The recorded lineshapes are fitted with standard Voigt line profiles in order to determine the collisional broadening coefficient of carbon dioxide transitions.     

Diode laser spectroscopy of He,N2 and air broadened water vapour transitions belonging to the (2ν1 + ν2 + ν3) overtone band

The line shape parameters of rovibrational transitions of water vapour belonging to the (2ν₁ + ν₂ + ν₃) overtone band due to collisions between absorber molecules and noble gas helium have been measured in the spectral range between 11988.494 cm^?1 and 12218.829 cm^?1 using NIR diode laser spectrometer. In addition nitrogen and air broadening effects on some water vapour transitions belonging to the same band have also been studied. Wavelength modulation spectroscopy along with phase sensitive detection technique are used to record first derivative (1f) signal of buffer gas broadened water vapour transitions. Observed line shapes are fitted to standard Voigt profiles by non-linear least squares fitting program to extract the line shape parameters, like line strength and pressure broadening coefficients. The broadening effects induced by different types of buffer gases on water vapour line shapes are compared. Rotational quantum number (J) dependence of broadening coefficients of water vapour transitions is also examined.     

Measurements and calculations of H2-broadening and shift parameters of water vapour transitions of the ν1 + ν2 + ν3 band

The water vapour line broadening and shifting for 97 lines in the ν₁ + ν₂ + ν₃ band induced by hydrogen pressure are measured with Bruker IFS 125 HR FTIR spectrometer. The measurements were performed at room temperature, at the spectral resolution of 0.01 cm^?1 and in a wide pressure range of H₂. The calculations of the broadening γ and shift δ coefficients were performed in the semi-classical method framework with use of an effective vibrationally depended interaction potential. Two potential parameters were optimised to improve the quality of calculations. Good agreements with measured broadening coefficients were achieved. The comparison of calculated broadening coefficients γ with the previous measurements is discussed. The analytical expressions that reproduce these coefficients for rotational, ν₂, ν₁, and ν₃ vibrational bands are presented.     

13CH4分子v3振动带空气和氮气加宽系数温度依赖性研究

采用中红外波段连续可调谐二极管激光器和自行研制的低温吸收池, 测量了温度为296 K, 252 K, 213 K, 173 K时, 3.38 μm附近¹³CH₄分子的四条跃迁谱线的氮气和空气加宽光谱; 首次通过实验获得空气和氮气对¹³CH₄分子的碰撞加宽系数, 以及谱线加宽系数的温度依赖系数. 实验过程中, 利用Voigt线型对所测量的光谱进行拟合. 实验结果表明, 氮气和空气对¹³CH₄分子的碰撞诱导加宽系数随温度的降低而增大; 相同温度下, 氮气对¹³CH₄分子的碰撞加宽系数普遍大于空气加宽系数. 实验数据为地球和外星体大气遥感探测提供了依据.     

Diode laser measurements of temperature-dependent collisional-narrowing and broadening parameters of Ar-perturbed H2O transitions at 1391.7 and 1397.8 nm

High-resolution absorption lineshapes of two H₂O transitions near 7185.60 and 7154.35 cm⁻¹ have been recorded in a heated static cell as a function of temperature (296-1100 K) and pressure (6-830 Torr) using two distributed-feedback diode lasers. The measured absorption spectra are least squares fit to both Voigt and Galatry profiles. Strong collisional-narrowing effects are observed in the Ar-broadened H₂O spectra at near-atmospheric pressure due to the relatively weak collisional broadening induced by Ar-H₂O collisions, while collisional narrowing is not significant for pure H₂O absorption lineshapes. Line strengths and self-broadening coefficients are inferred from the pure H₂O absorption spectra and compared with published data. Temperature dependences of the Ar-induced broadening, narrowing, and shift coefficients are determined using Galatry fits to the absorption data. The measured collisional-narrowing parameters have similar temperature dependence to the collisional-broadening coefficients.     

H2-broadening,shifting and mixing coefficients of the doublets in the ν2 and ν4 bands of PH3 at room temperature

The broadening, shifting and mixing coefficients of the doublet spectral lines in the ν₂ and ν₄ bands of PH₃ perturbed by H₂ have been determined at room temperature. Indeed, the collisional spectroscopic parameters: intensities, line widths, line shifts and line mixing parameters, are all grouped together in the collisional relaxation matrix. To analyse the collisional process and physical effects on spectra of phosphine (PH₃), we have used the measurements carried out using a tunable diode-laser spectrometer in the ν₂ and ν₄ bands of PH₃ perturbed by hydrogen (H₂) at room temperature. The recorded spectra are fitted by the Voigt profile and the speed-dependent uncorrelated hard collision model of Rautian and Sobelman. These profiles are developed in the studies of isolated lines and are modified to account for the line mixing effects in the overlapping lines. The line widths, line shifts and line mixing parameters are given for six A₁ and A₂ doublet lines with quantum numbers K = 3n,?(n = 1,?2, …) and overlapped by collisional broadening at pressures of less than 50 mbar.     

Low-pressure line shape study of acetylene transitions in the ν 1 + ν 2 + ν 4 + ν 5 band over a range of temperatures

In this study we have retrieved the self-broadened widths, self-pressure-induced shifts, and Dicke narrowing coefficients for 20 R-branch transitions in the ν₁?+?ν₂?+?ν₄?+?ν₅ band of acetylene. The spectra were recorded using a three-channel diode laser spectrometer, a temperature-controlled cell of fixed length and a second, room temperature cell. The soft collision (Galatry) and hard collision (Rautian) profiles with inclusion of line mixing effects were used to retrieve the line parameters. We determined the temperature dependencies for line broadening, shift, and Dicke narrowing coefficients. We performed comparisons between our retrieved line parameters and published line parameters for acetylene transitions.     

High-resolution cavity ring-down spectroscopy measurements of blended H<Subscript>2</Subscript>O transitions

We probed four closely spaced rovibrational water vapor absorption transitions near =7100 cm^-1 using frequency-stabilized cavity ring-down spectroscopy. Room-temperature spectra were acquired for pure water vapor in the Doppler limit and for mixtures containing ≈6.6 μmol mol^-1 of water vapor in N₂ at total gas pressures ranging from 6.5 kPa to 53 kPa. By measuring Lamb dips for each transition, we demonstrated a resolution of 50 kHz and determined relative transition frequencies with an uncertainty <0.4 MHz over a 10 GHz range. Pressure-induced broadening, collisional narrowing coefficients of the component transitions and line areas were retrieved by fits of model line shapes to the measured spectra. Standard and advanced models were considered including those which incorporated the combined effects of collisional narrowing and speed-dependent line broadening and line shifting. By measuring water vapor concentration with a transfer standard hygrometer, we determined line intensities in terms of measured line areas with a combined relative uncertainty of 0.6%. PACS 33.20.-t; 33.70.Jg; 33.70.Fd; 42.62.Fi     

Computations of temperature dependences for line shape parameters in the 30012 ← 00001 and 30013 ← 00001 bands of pure CO2

In this study, we have calculated the broadening and first order line mixing parameters for over 100 transitions in the 30012 ← 00001 and 30013 ← 00001 bands of carbon dioxide. The calculations were performed over the 193–323 K temperature range for pure CO₂ and lean mixtures of CO₂ and air. The elements of the relaxation matrices were calculated at the appropriate physical conditions using the Exponential Power Gap (EPG) and Energy Corrected Sudden (ECS) scaling laws. We have compared our calculated low pressure line mixing parameters and the broadening coefficients with experimental results from two previous studies in our group available at 217, 234, 258 and 296 K. At all temperatures, the calculated broadening coefficients were also compared with those available in the HITRAN database.     

Diode laser absorption spectroscopy measurement of linestrengths and pressure broadening coefficients of the methane 2ν3 band at elevated temperatures

A diode laser sensor based on absorption spectroscopy has been developed for the measurement of spectroscopic parameters in the R (3) and R (4) manifolds of 2ν₃ band of CH₄. Individual linestrengths of each transition are determined for a range of temperatures. In addition, collision-broadened half-widths for CO₂, N₂, H₂O, CH₄, and CO collision partners are measured as a function of temperature and pressure for these strongly overlapped transitions. From this, temperature dependence of the collision half-width for each collision partner is determined. Using a new method for calculation of collisional broadening at high temperatures for strongly overlapped transitions makes these transitions accessible for spectroscopy.     

Spectral Intensity and Lineshape Measurements in the First Overtone Band of HF Using Tunable Diode Lasers

High-resolution absorption lineshapes for the P(3) and P(6) transitions of the first overtone (v = 2-0) band of HF at 296 K have been measured using a pair of distributed feedback diode lasers operating near 1.31 and 1.34 μm, respectively. Spectral line intensities and self-broadening parameters were determined by fitting the measured spectra with Voigt, Galatry, and Rautian lineshape models. Voigt profiles fit the low-pressure (<10 Torr) spectra of the P(3) transition reasonably well due to the relatively strong collisional broadening effect. Lineshape measurements of the P(6) transition (for pressures ranging from 5 to 60 Torr) show significant variation from the Voigt lineshape model due to velocity-changing collisions that effectively reduce the Doppler component of the spectral line. Lineshape models that include motional (Dicke) narrowing effects, Galatry (soft collision) and Rautian (hard collision) profiles yield significant improvements in the spectral lineshape fits compared with Voigt profiles. The collisional broadening coefficient (gamma) of the P(6) transition obtained from a Voigt fit is approximately 4% lower than those found with either Galatry or Rautian profile fits. The measured intensities and self-broadening coefficients are compared with values in the HITRAN database and previous measurements. Copyright 1999 Academic Press.     

N2-, H2-, and He-induced collisional broadening of the J = 24 ← 23 transition of HC3N located near 218.3 GHz at different temperatures

We report on experimental collisional relaxation of the J = 24 ← 23 line of HC₃¹⁴N, located near 218.3 GHz, induced by nitrogen, hydrogen, and helium. The measurements were carried out at selected temperatures in the 235-350 K range using a video-type spectrometer. The foreign gas broadening parameters and their temperature dependences were determined assuming Voigt lineshape profiles and the usual T⁻ⁿ temperature law. The experimental broadening parameters are compared with results derived using the ATC collisional formalism.     

Diode laser spectroscopic measurement and impact theoretical analysis of collision broadening of acetylene band transitions

A near infrared diode laser spectrometer has been used for measurement of line shapes of the rotational transitions of the () overtone-combination band of acetylene perturbed by oxygen and air. Pressure-broadening coefficients and line strength parameters are extracted from least squares fitting of the spectra with Voigt profiles. A detailed calculation of pressure-broadening coefficients for the self, nitrogen and oxygen broadening cases has been performed by using semi-classical impact theory based on quadrupolar and dispersion interactions. The relative importance of the intermolecular interactions has been investigated and it is found that for these weak interaction cases dispersive terms have a dominant role in line broadening. This is more pronounced for the O₂-broadening case. We have included all the non-resonant terms till convergence is achieved. The cutoff parameter b₀ of the Anderson procedure has been determined separately for each non-resonant process. In order to include the orientation effect of the molecules at the moment of collision we have considered an average kinetic collision diameter which sets the lower limit of b₀. This improves the result considerably and the calculated values are close to the observed results. The J-dependence of the half width is also reported and shows decrease for large J-values. Received 24 November 1999     

Water vapor line width and shift calculations with accurate vibration-rotation wave functions

Calculations of H₂¹⁶O rotation-vibration line broadening and shifting due to N₂ pressure effects are performed using a semi-empirical approach. The calculations are based on impact theory modified by introducing additional parameters to extend the use of empirical data. These model parameters are determined by fitting the broadening and shifting coefficients to experimental data. The method is further developed by using anharmonic wavefunctions in the estimates of the line profiles. The main feature of the present calculation is the use of a complete set of high-accuracy vibration-rotation dipole transition moments calculated for all possible transitions using wavefunctions determined from variational nuclear motion calculations and an ab initio dipole moment surface. This approach explicitly takes into account all scattering channels induced by collisions. Results of these calculations clearly demonstrate improved agreement between observed and calculated parameters for both the line widths and the line shifts.     

Study of the HF overtone line profile broadened by Ar,Xe, Kr,N2 using near-IR region diode laser spectroscopy

The profile of the 0-2 R(0) overtone vibrational-rotational absorption line of HF molecules in mixtures with Ar, Xe, Kr, N₂ is experimentally studied using near-IR-range diode laser spectroscopy. The coefficients of collisional broadening, shift, and collisional narrowing of the HF line in these buffer gases are determined using the Voigt, Rautian, and Galatry profiles.     

Xe-broadening coefficients of 12CH3D: a test of theoretical line shapes

We present the Xe-broadening coefficients for six lines belonging to the ν₃ band of ¹²CH₃D measured at room temperature with a diode-laser spectrometer. The collisional widths are obtained from least-squares fitting of each absorption line with theoretical line shapes. We used the well-known Voigt profile, the soft and hard collision models considering the collisional narrowing and also line shapes taking into account the speed dependence of the collisional cross-section. The results derived by these different models are compared with each other and with theoretical broadening coefficients. The calculations are based on a semiclassical impact formalism that includes the atom–atom Lennard–Jones potential for CH₃D–Xe interactions in which CH₃D is considered as a linear molecule.     

Experimental and theoretical study of line shift and mixing in the ν4 band of NH3 perturbed by N2

The shift coefficients and line-mixing parameters of rovibrational-inversion transitions in the ν₄ band of ammonia (NH₃) perturbed by nitrogen (N₂) have been measured at room temperature with a high-resolution Fourier transform spectrometer. The collisional shift and line mixing are obtained from the non-linear least-square multi-pressure fitting techniques. Comparison is made with the results of theoretical calculation based on semi-classical model extended to the case of symmetric top molecule with inversion motion. The shifts and the line-mixing parameters are calculated using, respectively the approach developed by Robert and Bonamy and the state-to-state cross-section. The agreement is satisfactory on the average. Good agreement is also obtained for line mixing with previous measurements.     

Study of the parameters of the collisionally broadened R22 absorption line of the 1000-0001 transition in CO2 molecules: I. Experiment

Unsaturated absorption coefficients in pure carbon dioxide at pressures of 1 and 100 Torr and in CO₂-N₂ and CO₂-He binary mixtures at a pressure of 100 Torr have been measured in the temperature range of 296?C700 K using a frequency-stabilized tunable CO₂ laser. The collisional self-broadening coefficient, the relative coefficients of collisional broadening caused by N₂ and He buffer gases, and their temperature dependences have been determined for the R22 absorption line of the 10⁰0?C00⁰1 transition in CO₂ molecules.