Jean Vander Auwera

Overtone spectroscopy in nitrous oxide

The near infrared and visible absorption spectrum of nitrous oxide 14N216O has been recorded by Fourier transform absorption spectroscopy, between 6500 and 11 000 cm−1, and by Intracavity Laser Absorption Spectroscopy, between 11 700 and 15 000 cm−1. Nineteen new bands are observed and, altogether, 34 cold and 10 hot bands are rotationally analyzed. The related upper term values, vibrational assignments, and principal rotational constants, as well as the relative band intensities are quantitatively discussed in terms of the formation of vibrational clusters, on the basis of the effective Hamiltonian developed by J. L. Teffo, V. I. Perevalov and O. M. Lyulin [J. Mol. Spectrosc. 168, 390 (1994)].

Predictive Abilities of Scaled Quantum Mechanical Molecular Force Fields: Application to 1,3-Butadiene

The positions of some IR bands of the s-trans-1,3-butadiene-h6 and -1,1,2-d3 isotopomers in the gas phase have been measured using a Brucker IFS 120 HR spectrometer with a resolution of 2 cm−1. The structural parameters of the s-trans- and s-gauche-1,3-butadiene conformers were optimized completely at the MP2/6-31G* theoretical level and their MP2/6-31G*//MP2/6-31G* quantum mechanical force fields (QMFFs) were calculated. Using only the experimental vibrational frequencies of s-trans-1,3-butadiene-h6 the QMFF of the s-trans conformer was corrected by Pulays scaling method (eight scale factors were involved). The scaled QMFF was used to calculate the mean vibrational amplitudes and the Coriolis coupling constants of s-trans-1,3-butadiene-h6 and the vibrational frequencies of 12 of its deuterated isotopomers. The set of scale factors obtained for correction of the s-trans QMFF was transferred to the QMFF of the s-gauche conformer. Its theoretical vibrational spectrum and those of some deuterated and C13 isotopomers were calculated. The ability of this scaling approach (transferring of scale factors) to predict the vibrational frequencies of rotational conformers and their isotopomers, as well as other molecular characteristics, and to permit detection of perturbations of the experimental bands are discussed.

Global analysis of the high temperature infrared emission spectrum of 12CH4 in the dyad (ν2/ν4) region

We report new assignments of vibration-rotation line positions of methane ((12)CH4) in the so-called dyad (ν2/ν4) region (1100-1500 cm(-1)), and the resulting update of the vibration-rotation effective model of methane, previously reported by Nikitin et al. [Phys. Chem. Chem. Phys. 15, 10071 (2013)], up to and including the tetradecad. High resolution (0.01 cm(-1)) emission spectra of methane have been recorded up to about 1400 K using the high-enthalpy source developed at Institut de Physique de Rennes associated with the Fourier transform spectrometer of the SOLEIL synchrotron facility (AILES beamline). Analysis of these spectra allowed extending rotational assignments in the well-known cold band (dyad-ground state (GS)) and related hot bands in the pentad-dyad system (3000 cm(-1)) up to Jmax = 30 and 29, respectively. In addition, 8512 new transitions belonging to the octad-pentad (up to J = 28) and tetradecad-octad (up to J = 21) hot band systems were successfully identified. As a result, the MeCaSDa database of methane was significantly improved. The line positions assigned in this work, together with the information available in the literature, were fitted using 1096 effective parameters with a dimensionless standard deviation σ = 2.09. The root mean square deviations dRMS are 3.60 × 10(-3) cm(-1) for dyad-GS cold band, 4.47 ×10(-3) cm(-1) for the pentad-dyad, 5.43 × 10(-3) cm(-1) for the octad-pentad, and 4.70 × 10(-3) cm(-1) for the tetradecad-octad hot bands. The resulting new line list will contribute to improve opacity and radiative transfer models for hot atmospheres, such as those of hot-Jupiter type exoplanets.

THE GROUND ELECTRONIC STATE OF 1,2-DICHLOROETHANE . II. EXPERIMENTAL INVESTIGATION OF THE FUNDAMENTAL AND OVERTONE VIBRATIONS

The absorption spectrum of 1,2-dichloroethane has been recorded under various experimental conditions, between 50cm-1 and 10 000cm-1 using Fourier transform spectroscopy, and between 10 800cm-1 and 17 400cm-1 using optoacoustic laser spectroscopy. The assignment of the fundamental bands of the trans and gauche isomers was confirmed using in particular the results of recent ab initio calculations (El Youssoufi et al., 1998, Molec. Phys., 94, 461). The first overtone and combination bands were assigned for the first time using a variety of criteria including the band type and, in some cases, the spacing between clumps of rotational lines. Emphasis is placed on the CH progression of bands. Most of the results concern bands from the more abundant trans isomer, up to the near infrared range. Bands are tentatively assigned to the gauche species in the mid and near infrared regions and to the trans rotamer in the visible range. Vibrational frequencies and anharmonic parameters are obtained.

New investigation of the ν3 C–H stretching region of 12CH4 through the analysis of high temperature infrared emission spectra

The ν3 C-H stretching region of methane was reinvestigated in this work using high temperature (620-1715 K) emission spectra recorded in Rennes at Doppler limited resolution. This work follows our recent global analysis of the Dyad system Δn = ±1 (1000-1500 cm-1), with n being the polyad number [B. Amyay et al., J. Chem. Phys. 144, 24312 (2016)]. Thanks to the high temperature, new assignments of vibration-rotation methane line positions have been achieved successfully in the Pentad system and some associated hot bands (Δn = ±2) observed in the spectral region 2600-3300 cm-1. In particular, rotational assignments in the cold band [Pentad-ground state (GS)] and in the first related hot band (Octad-Dyad) were extended up to J = 30 and 27, respectively. In addition, 1525 new transitions belonging to the Tetradecad-Pentad hot band system were assigned for the first time, up to J = 20. The effective global model used to deal with the new assignments was developed to the 6th order for the first three polyads (Monad, Dyad, and Pentad), and to the 5th order for both the Octad and the Tetradecad. 1306 effective parameters were fitted with a dimensionless standard deviation σ = 2.64. The root mean square deviations dRMS obtained are 4.18 × 10-3 cm-1 for the Pentad-GS cold band, 2.48 × 10-3 cm-1 for the Octad-Dyad, and 1.43 × 10-3 cm-1 for the Tetradecad-Pentad hot bands.

Spectroscopic investigation of the response of the NO2-N2O4 chemical system to optical laser pumping

Abstract An argon laser beam was used to perturb the NO2-N2O4 chemical system. The perturbation was monitored, in different experiments, with the laser-induced fluorescence and the IR optical double-resonance (IODR) techniques. The expected quantum perturbations which involve specific rotational levels in NO2, X 2A1 were observed. Unexpected chemical effects which involve the ground state concentration of both species and which are attributed to the response of the chemical equilibrium to the optical perturbation were also observed. The IODR results are discussed with the help of a model based on the Beer-Lambert law, which allows the role of the chemical response to be demonstrated.

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].

Quantitative Laboratory Spectroscopy of Atmospheric Trace Gases

The analysis of spectra of the terrestrial atmosphere recorded using remote sensing techniques requires reference spectroscopic information, measured in the laboratory. This article describes laboratory measurements of reference absolute absorption intensities for atmospheric trace species using Fourier transform spectroscopy in the infrared spectral range. Emphasis is put on measurements of quantitative information for chemically unstable species.

Infrared absolute line intensities for minor atmospheric constituents

We present recent laboratory measurements of absolute line intensities for carbonyl sulfide and nitrous oxide in the infrared and near infrared spectral ranges respectively, using high-resolution Fourier transform spectroscopy.