Rautian Profile Research Articles

Hydrogen-Broadening Coefficients in the ν 5 Band of Acetylene at Low Temperature

H 2-broadening coefficients have been measured for 29 lines of C 2H 2 at 173.2 K in the P and R branches of the ν 5 fundamental band near 13.7 μ m, using a tunable diode-laser spectrometer. These lines were individually fitted with a Voigt and a Rautian profile in order to determine the collisional widths. The resulting broadening coefficients are compared with values calculated from a semiclassical theory performed by considering, in addition to electrostatic interactions, the atom–atom Lennard–Jones model. A satisfactory agreement is obtained but only for low and medium J values. 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.

O2 broadening of carbon disulphide 12C32S2 in the v 3 and v 3—v 1 bands

Using a tunable diode laser spectrometer, we have measured O2 broadening coefficients of 12C32S2 for 31 lines in the v 3 fundamental band near 6.5 μm and 12 lines in the v 3—v 1 band near 11.4 μm. The collisional halfwidths are obtained by fitting the spectral lines with a Voigt and a Rautian profile. The broadening coefficients of 12C32S2-O2 are also calculated from semiclassical theory involving, in addition to electrostatic interactions, successively the atom-atom Lennard-Jones model and a simple formulation for the anisotropic dispersion forces, leading to more satisfactory results.

N2-Broadening Coefficients in the ν1 Band of 35Cl12C14N

N2-broadening coefficients have been measured for 30 lines of cyanogen chloride (35Cl12C14N) at room temperature in the P and R branches of the ν1 band, using a tunable diode–laser spectrometer. These lines, with J values ranging from 0 to 55, are located in the spectral range 694–736 cm−1. The collisional widths are obtained by fitting the spectral lines with a Voigt and a Rautian profile. The broadenings coefficients of 35ClCN–N2 have also been calculated from a semiclassical theory involving the atom–atom Lennard–Jones model for the intermolecular potential in addition to electrostatic interaction.

Diode–Laser Measurements of N2-Broadening Coefficients in the ν7 Band of C2H4

N2-broadening coefficients have been measured for 35 lines of C2H4 in the ν7 fundamental transition, using a tunable diode–laser spectrometer. These lines with 3 ≤ J" ≤ 23, 0 ≤ Ka″ ≤ 4, and 1 ≤ Kc″ ≤ 22 are located in the spectral range 880–1024 cm−1. The collisional half-widths are obtained by modeling each spectral line with a Voigt and a Rautian profile. The measured broadening coefficients belonging to transitions with the same J" generally increase with increasing Ka″ and the coefficients decrease on the whole with increasing J". These behaviors can be predicted by an approximate semiclassical calculation performed by approximating ethylene to a prolate symmetric-top molecule.

N2 Broadening of Carbon Disulfide 12C32S2 in the ν3 and ν3–ν1 Bands

N2 broadening coefficients have been measured for 33 lines in the ν3 fundamental band and 21 lines in the ν3–ν1 band of C32S2, using a tunable diode–laser spectrometer. These lines with J values ranging from 0 to 78 in the ν3 band and from 4 to 70 in the ν3–ν1 band are located in the spectral ranges 1514–1548 and 853–887 cm−1, respectively. The collisional widths are obtained by fitting the spectral lines with a Voigt and a Rautian profile. Semiclassical calculations of these broadening coefficients have been performed by considering, in addition to electrostatic interactions, successively the atom–atom Lennard–Jones model and a simple formulation for the anisotropic dispersion forces leading to more satisfactory results.

Asymmetries and correlations in speed-dependent Dicke-narrowed line shapes of argon-broadened HF

Asymmetric line shapes observed for infrared transitions of Ar-broadened HF [A.S. Pine, J. Chem. Phys. 101, 3444 (1994)] were fit to Dicke-narrowed profiles with an empirical partial correlation between velocity- and phase-changing collisions. That analysis yielded measured broadening and shifting coefficients in excellent agreement with the thermally averaged values calculated by Green and Hutson [J. Chem. Phys. 100, 891 (1994)] from quantum close-coupled scattering cross-sections based on a realistic van der Waals potential. However, some anomalies in the sense of the asymmetries at low J and the magnitude and J dependence of the velocity-changing rates were noted, and are reexamined here by incorporating speed dependence into the collision parameters of the correlated Rautian profile. The speed dependence of the parameters is calculated from the reliable energy-dependent cross-sections of Green and Hutson. For HF/Ar below one atmosphere, we find that deviations from the conventional Voigt profile are dominated by correlated Dicke narrowing rather than speed-dependent effects, but the latter explain the anomalous asymmetries at low J.

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

High-resolution absorption lineshapes for theP(3) andP(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 theP(3) transition reasonably well due to the relatively strong collisional broadening effect. Lineshape measurements of theP(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 (γ) of theP(6) transition obtained from a Voigt fit is ∼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.

Analysis of O2-Broadening of12CH3F Lines in the 6.8-μm Spectral Region

Using a tunable diode-laser spectrometer, we have measured the O2-broadening coefficients for 45 lines of methyl fluoride in theQPandQRbranches of the ν2parallel band, and in thePP,PQ,PR,RP,RQ, andRRbranches of the ν5perpendicular band. These lines withJvalues ranging from 1 to 23 andKfrom 0 to 9 (K ≤ J) are located in the spectral range 1416–1573 cm−1. The collisional halfwidths are obtained by modeling each spectral line with a Voigt and a Rautian profile. The noncorrelated Rautian model leads to larger values of broadening coefficients than the Voigt model. These coefficients have also been calculated from a semiclassical model in which the intermolecular potential includes electrostatic, induction, and dispersion energy contributions. The results in theP,Q, andRbranches of the ν2and ν5bands are in overall agreement with the experimental data.

On the Speed-Dependent Hard Collision Lineshape Models: Application to C2H2Perturbed by Xe

Three infrared absorption lines of the ν5band of C2H2diluted by Xe at pressures ranging from 40 to 300 mbar have been recorded at high resolution near 750 cm−1, using a tunable diode-laser spectrometer. Their lineshapes have been first analyzed by means of models using either the Dicke narrowing effect or the absorber speed-dependent collisional broadening and shifting. None of these models have given satisfactory results over the full pressure range of the perturber. It is shown that a correct treatment must include both line narrowing effects. We have investigated two possibilities of doing so: a convolution between two profiles corresponding to each effect and a noncorrelated and speed-dependent Rautian profile that we have developed here. The latter lineshape model appears to be the most appropriate.

Diode-Laser Measurements of H2-Broadening Coefficients in the ν2Band of HCN

H2-broadening coefficients have been measured for 34 absorption lines of hydrogen cyanide (H12C14N) in theP,Q, andRbranches of the ν2band, using a tunable diode-laser spectrometer. These lines withJvalues ranging from 2 to 26 are located in the spectral range 658–780 cm−1. The collisional widths are obtained by modeling each spectral line with a Voigt and a Rautian profile. A semiclassical calculation of these collisional broadening provides results in satisfactory overall agreement with the experimental data in thePandRbranches as well as in theQbranch.

Line Intensities in the ν6Band of CH3F at 8.5 μm

Infrared absolute line intensities of the ν6band of CH3F have been measured around 8.5 μm using a diode-laser spectrometer. These line strengths were obtained by the equivalent width method and, for 13 lines, by fitting a Rautian profile to the measured shape of the lines. From these results, we have deduced the vibrational band strength to beS0v= 9.66 ± 0.13 cm−2atm−1at 296 K and the first Herman–Wallis factors.

Absolute Line Intensities in the ν3Band of12CH3F by Diode-Laser Spectroscopy

Infrared absolute line intensities of the ν3band of12CH3F have been measured around 9.5 μm using a diode-laser spectrometer. These line strengths were obtained from the equivalent width method and, for a few lines, by fitting a Rautian profile to the measured shape of the lines. From these results, we have deduced the vibrational bandstrength (Sv0= 379.2 ± 5.9 cm−2·atm−1at 296 K) and the first Herman–Wallis factor (α = 0.35 × 10−3± 0.10 × 10−3).