Muriel Lepère

The bending vibrations in 12C2H2: global vibration–rotation analysis

A total of 3155 vibration–rotation line positions providing accurate information on all known vibration–rotation states up to 3000 cm−1 in 12C2H2 were gathered from the literature. An additional 966 lines were assigned on new spectra. The full data set was simultaneously fitted using an appropriate Hamiltonian, with 85 refined parameters. A dimensionless standard deviation equal to 0.86, accounting for 92% of the lines, was achieved. The vibrational transition dipole moment of the υ5 = 1 ← υ4 = 1 band observed in the far-infrared was estimated to be |μ5←4| = 0.55 D with 20% accuracy, from absolute intensity measurements for a few Q-branch lines.

Diode-laser measurements of H2-broadening coefficients in the ν5 band of C2H2

Abstract H 2 -broadening coefficients have been measured for 34 absorption lines of hydrogen cyanide (H 12 C 14 N) in the P , Q , and R branches of the ν 2 band, using a tunable diode-laser spectrometer. These lines with J values 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 the P and R branches as well as in the Q branch.

H2-broadening in the ν7 band of ethylene by diode-laser spectroscopy

Abstract Using a tunable diode-laser spectrometer, we have measured H 2 -broadening coefficients for 34 lines of C 2 H 4 in the ν 7 fundamental band. The studied transitions J ′ , K a ′ , K c ′ ← J ″ , K a ″ , K c ″ with J ″ ranging from 2 to 23, K a ″ from 0 to 4, and K c ″ from 2 to 22 in the P , Q , and R branches are located in the spectral range 919– 1023 cm - 1 . The collisional 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 K a ″ and these coefficients decrease slightly on the whole with increasing J ″ . These behaviors can be roughly predicted by an approximate semiclassical calculation performed by using in addition to the weak electrostatic contributions a simple formalism for the contribution of the intermolecular potential.

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.

Measurements and calculations of ethylene line-broadening by argon in the ν7 band at room temperature

Argon broadening coefficients are measured for 32 vibrotational lines in the ν7 band of ethylene at room temperature using a tunable diode-laser spectrometer. These lines with 3 ≤ J ≤ 19, 0 ≤ Ka ≤ 4, 2 ≤ Kc ≤ 19 in the P, Q and R branches are located in the spectral range 919–1023 cm−1. The fitting of experimental line shapes with Rautian profile provides collisional widths slightly larger than those derived from the Voigt profile. The independent theoretical estimation of these line widths is performed by the semiclassical approach of Robert-and-Bonamy type with exact isotropic trajectories generalized to asymmetric tops. Even with a rough atom–atom intermolecular potential model the calculated values show good agreement with experimental results.

Absolute intensity measurements in the ν3 band of carbon disulphide

The aim of this paper is to determine with accuracy the band strength of the strong ν3 fundamental band of carbon disulphide CS2. By diode-laser spectroscopy, we have measured line by line the intensities for the 12C32S2 form by the equivalent width method and by the line profile fitting method. To confirm our results, we have also measured 30 lines for the 13C32S2 isotopic species using a sample of CS2 in natural abundance. We have obtained for the band strength S0 v = 1417 cm−2 atm−1 at 296 K and this value is in good agreement with the values from the literature.

Molecular dynamic simulations of N2-broadened methane line shapes and comparison with experiments

Absorption spectra of methane transitions broadened by nitrogen have been calculated for the first time using classical molecular dynamic simulations. For that, the time evolution of the auto-correlation function of the dipole moment vector, assumed along a C–H axis, was computed using an accurate site-site intermolecular potential for CH4–N2. Quaternion coordinates were used to treat the rotation of the molecules. A requantization procedure was applied to the classical rotation and spectra were then derived as the Fourier-Laplace transform of the auto-correlation function. These computed spectra were compared with experimental ones recorded with a tunable diode laser and a difference-frequency laser spectrometer. Specifically, nine isolated methane lines broadened by nitrogen, belonging to various vibrational bands and having rotational quantum numbers J from 0 to 9, were measured at room temperature and at several pressures from 20 to 945 mbar. Comparisons between measured and calculated spectra were ma...

Erratum/ The bending vibrations in 12C2H2: Global vibration-rotation analysis (Molecular Physics (2007) 105:5 (559-568))

The author of this paper would like to change the following: The vibrational transition dipole moment of the 5– 4 FIR band determined to be 5 4 j j 1⁄4 0.55 D is incorrect. Indeed, it was found that the wavenumber ~ of the lines was overlooked in its determination from the measured line intensities. The correct value is 5 4 j j 1⁄4 0.051 D. It is comparable to that measured for C2D2, i.e. 0.0358 (20) D [1].

Absolute line intensities in the v3 band of 12CH3F at 9.6 μm

Abstract Infrared absolute line intensities of the v 3 band of 12 CH 3 F have been measured around 9.5 μm using a diode-laser spectrometer. We have deduced the vibrational band-strength to be S 0 v = 377.9 ± 5.9 cm −2 atm −1 at 296 K and the first Herman-Wallis factor.

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

ABSTRACT 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.