N2-broadening coefficients in the ν4 band of CH4 at room temperature

Using a diode laser spectrometer, we have studied with a great accuracy the N₂-broadening coefficients in the ν₄ band of methane. The experiments were performed at room temperature for lines in the P- and R-branches. We have measured 39 lines in the spectral range 1237–1373 cm⁻¹ with J values between 1 and 12. Each line under study was recorded at four different nitrogen pressures, ranging from 20 to 91 mbar. The collisional half-widths were obtained by fitting individually a theoretical profile on the experimental profile of each line at each N₂-pressure. We fitted the usual Voigt profile, but also the Rautian and Galatry lineshape models which take into account the collisional narrowing due to the molecular confinement (Dicke effect). The Rautian and Galatry fits are always better adjusted on the experimental profiles. For some lines, when the overlapping could not be disregarded, a fit of the blended profiles was performed using the same lineshape models. The collisional broadening coefficients obtained with Galatry and Rautian models are nearly equal and always higher than those derived from Voigt profile. Finally, we compare our results with previous determinations realized for several absorption bands.     

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 coefficients in the ν3 band of CH3D at low temperatures

Using a diode-laser spectrometer, we have measured H₂-broadening coefficients of CH₃D at low temperatures (153.5, 183.5, and 223.5 K) for four lines in the ν₃ band. The collisional widths are obtained by fitting each absorption line with three lineshape models: the Voigt, Rautian, and Galatry profiles. The broadening coefficients are also calculated on the basis of a semiclassical model of interacting linear molecules by considering an atom-atom Lennard-Jones potential in addition to electrostatic contributions. By comparing the broadening coefficients at room and low temperatures the temperature dependence of these broadenings has been determined both experimentally and theoretically.     

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.     

Self-broadening coefficients in the ν4 band of CH4 by diode-laser spectroscopy

With a diode-laser spectrometer, we have measured self-broadening coefficients of 42 lines of the P-, Q- and R-branches in the ν₄ fundamental band of CH₄ at room temperature, with J values ranging between 1 and 12. For the determination of self-broadening parameters, we have fitted to the experimental lineshape two theoretical line profiles: the Voigt profile taking into account Doppler and collisional broadenings, and the hard collision model developed by Rautian and Sobel’man incorporating Dicke narrowing.     

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.     

Absolute Line Intensities and Self-Broadening Coefficients in the nu(1) Band of (35)Cl(12)C(14)N

The self-broadening coefficients and the intensities of 29 lines in the nu(1) band of cyanogen chloride ((35)Cl(12)C(14)N) have been measured at high resolution in the range 699-736 cm(-1), using a tunable diode-laser spectrometer. The collisional widths and most of the intensities are obtained by fitting Voigt and Rautian profiles to the measured shapes of the lines. From the analysis of the line intensities we determine the absolute strength as well as the Herman-Wallis factors for the nu(1) band. A semiclassical calculation of the self-broadening coefficients, performed by considering the main electrostatic interactions only, has provided larger results than the experimental data. Copyright 2001 Academic Press.     

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.     

CO2-broadening coefficients in the ν4 + ν5 band of acetylene

The CO₂-broadening coefficients of 24 P- and R-branch transitions in the ν₄ + ν₅ band of acetylene were measured at room temperature using a diode-laser spectrometer. These lines with J values up to 26, were located in the spectral range 1270 to 1400 cm⁻¹. The collisional broadening coefficients were retrieved by fitting the experimental profiles to the Voigt, Rautian, and Galatry lineshape models. Two experimental values for the narrowing coefficient were determined from the spectra and compared with the theoretical narrowing coefficient. The calculations of these broadenings were also performed in the frame of a semiclassical formalism involving a simple intermolecular potential with an adjustable parameter. The theoretical results are in good agreement with the experimental results and reproduce well the J dependence of the broadening coefficients.     

Self-broadening coefficients in the ν2 and ν5 bands of CH3F at 183 and 298 K

The self-broadening coefficients of 33 rovibrational lines in the ν₂ and ν₅ bands of ¹²CH₃F were measured at a sample temperature of 183 K using a diode-laser spectrometer. We have also realized the measurement of these coefficients at room temperature for 10 of these lines in order to determine their temperature dependence. These results were obtained by fitting to the experimental profile the Voigt lineshape and the Rautian and Galatry models taking into account the collisional narrowing. Calculations of the self-broadening coefficients were also performed for the same temperatures from a semiclassical model involving only electrostatic interactions in the intermolecular potential. The calculated values are significantly larger than the experimental data for both temperatures but the J-dependences of the self-broadenings are well reproduced. Moreover, the theoretical temperature dependence of these coefficients is in good agreement with that derived from the measurements.     

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.     

N2-broadening coefficients in the ν3 band of CS2 at room and low temperatures

Using a tunable diode-laser spectrometer, N₂-broadening coefficients have been measured for 15 lines in the ν₃ band of C³²S₂ at room and low temperatures (298, 273.2, 248.2, 223.2, and 198.2 K). These lines with J values ranging from 2 to 62 are located in the spectral range 1519-1545 cm⁻¹. The collisional widths are obtained by fitting each measured spectral line with a Voigt and a Rautian lineshape model and for a few lines we also used a Galatry model. From these results, we have determined the n parameter of the temperature dependence of each broadening coefficient. A semiclassical calculation of these broadenings has been performed by considering in addition to the main electrostatic quadrupole-quadrupole interaction an anisotropic dispersion contribution leading to satisfactory results at all temperatures and providing the n temperature dependence parameter in good agreement with the experimental determination.     

High-Resolution Measurements of HBr Transitions in the First Overtone Band Using Tunable Diode Lasers

High-resolution absorption lineshapes of the R(7) and P(2) transitions in the first overtone (v = 0-2) band of H(79)Br have been recorded at room temperature using a pair of distributed feedback diode lasers operating near 1.95 and 2.00 μm, respectively. Spectral line intensities and self-broadening coefficients were determined by fitting the measured spectra (for various pressures P = 10-100 Torr) with Voigt profiles and compared with values in the literature. Measured line intensities for the P(2) and R(7) transitions are approximately 11 and 16% higher than those listed in the HITRAN database, respectively. The measured self-broadening coefficient of the P(2) transition is approximately 14% lower than the value listed in HITRAN. Measurements of the P(2) lineshapes at low pressure (100 mTorr) were modeled with eight-line Gaussian profiles based on ground state (v = 0) hyperfine constants to include the effects of nuclear electric quadrupole interactions. Copyright 2000 Academic Press.     

Oxygen Broadening of Acetylene Lines in the nu5 Band at Low Temperature

O2-broadening coefficients have been measured for 29 lines of C2H2 at 173.2 K in the P and R branches of the nu5 band near 14 μm, using a tunable diode-laser spectrometer. The collisional widths obtained by Rautian profiles closely fitting the measured spectral shape of the lines are slightly larger than those derived from Voigt profiles. The broadening coefficients are compared with results calculated from a semiclassical theory, performed by considering, in addition to electrostatic interactions involving the hexadecapole moments of C2H2 and O2, the atom-atom Lennard-Jones model. By comparing broadening coefficients at 297 and 173.2 K from a simple power law, the temperature dependence of these broadenings has been determined both experimentally and theoretically. Copyright 1999 Academic Press.     

Evidence for collisional narrowing in the infrared laser Stark spectrum of CH3CN

The infrared laser Stark lineshape of the Jkm = 211 ← 111 transition in the ν₄ band of CH₃CN was recorded under computer control at several pressures. Analysis of the lineshapes by means of the usual Voigt profile gives a plot of collision broadening vs pressure that shows marked curvature in the low-pressure region. In addition, extrapolation to zero pressure of the best straight line through the high-pressure points gives a negative intercept. By choosing an appropriate narrowing parameter in either of the limiting soft-collision or hard-collision models of collisional narrowing, it is possible to obtain plots of collision broadening vs pressure that are linear and have acceptable intercepts. The pressure broadening and collisional narrowing parameters derived are 69.4 ± 0.7 and 17.2 ± 1.7 MHz/Torr, respectively, for the soft-collision model and 68.6 ± 0.7 and 11.5 ± 1.2 MHz/Torr, respectively, for the hard-collision model.     

Self-broadening coefficients in the ν7 band of ethylene at room and low temperatures

Using a tunable diode-laser spectrometer, we have measured self-broadening coefficients for a few transitions in the ν₇ fundamental band of C₂H₄ at 298 and 174 K. The studied transitions J^′, K_a^′, K_c^′←J, K_a, K_c with 3?J?17, 1?K_a?4, and 1?K_c?14 are located in the spectral range 919-982 cm⁻¹. The collisional widths are measured by fitting each spectral line with Voigt, Rautian, and speed-dependent Rautian profiles. The latter model provides larger broadening coefficients than the Rautian profile and still larger coefficients than the Voigt profile. An approximate semiclassical calculation performed by considering only electrostatic interactions leads to reasonable agreement with the experimental data. By comparing the results obtained at room and low temperatures, the temperature dependence of the self-broadening has been determined both experimentally and theoretically.     

N2- and O2-broadening coefficients in the ν2 and ν5 bands of CH3F at 183 and 298 K

The N₂- and O₂-broadening coefficients of 33 rovibrational lines in the ν₂ and ν₅ bands of ¹²CH₃F were measured at 183 K using a diode-laser spectrometer. The measurement of these coefficients was also realized at room temperature for 10 of these lines to determine their temperature dependence. The line parameters were obtained by fitting to the experimental profile the Voigt lineshape, and the Rautian and Galatry models taking into account the collisional narrowing. Calculations of the pressure-broadening coefficients were also performed for the same temperatures from a semiclassical model involving electrostatic, induction and dispersion interactions in the intermolecular potential. The calculated values reproduce well the experimental data for both temperatures and both perturbers and the theoretical temperature dependence of the broadening coefficients is in satisfactory agreement with that derived from the measurements.     

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.     

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.     

Diode-Laser Measurements of N(2)-Broadening Coefficients in the nu(7) Band of C(2)H(4)

N(2)-broadening coefficients have been measured for 35 lines of C(2)H(4) in the nu(7) fundamental transition, using a tunable diode-laser spectrometer. These lines with 3 相似文献