R. Farrenq

Dunham coefficients for seven isotopic species of CO

An extensive work on vibration-rotation spectra in the fundamental 1Σ+ electronic state of CO is reported. More than 30 000 Doppler-limited measurements corresponding to about 8500 transitions of 255 bands of 12C16O, 12C18O, 13C16O, and 13C18O, most of them observed for the first time, have been obtained with a high information Fourier transform interferometer on the sequences Δv = 1, 2, and 3. The highest v and J values are 41 and 93, respectively. Experimental vibrational levels are then well observed up to three fourths of the dissociation energy limit. These accurate infrared wavenumbers, with an additional selected set of all previous measurements, have been simultaneously fitted to the Dunham expression in a weighted nonlinear least-squares calculation covering seven different isotopic species. It significantly improves both the number of parameters (U and Δ) obtained by the best previous work (35 instead of 23) and their corresponding standard deviations. The rms of the fit is equal to 13 × 10−6 cm−1 (390 KHz). Calculated wavenumbers from the 35 reduced Dunham and mass-scaling coefficients can then be used as secondary standards, even for transitions involving high v and J values of the various isotopic species. These new parameters should be a convenient and useful tool for several purposes, such as assignment of infrared laser lines and identification of microwave and infrared transitions in astronomical spectra. The Dunham coefficients Y are also reported for 12C16O, 12C17O, 12C18O, 13C16O, 13C17O, 13C18O, and 14C16O. These experimentally determined accurate Y should also be useful for further examination of the potential energy and dipole moment formulations.

12C16O2 analysis of emission Fourier spectra in the 4.5-μm region: Rovibrational transitions 0v2lv3-0v2l(v3 − 1), v2 = l

Abstract Emission spectra of CO2, vibrationally excited by a dc electric discharge, were recorded under Doppler-limited resolution, using a high-information Fourier transform interferometer, in the spectral range of 4–5 μm. Results concerning 49 vibrational transitions with Δv3 = 1 of 12C16O2 are reported. About 2000 wavenumbers, achieving at least a 10-fold improvement in accuracy over previous measurements for all the “hot” transitions, are given with an absolute uncertainty of the order of 10−4 cm−1 for the best of them. The band centers and the spectroscopic constants for all the vibrational levels involved are reported. They reproduce the experimental wavenumbers with a rms of the order of 2 × 10−5 cm−1 for the best vibrational transitions and 3 × 10−4 cm−1 for most of the others. From weighted simultaneous fits of all the experimental wavenumbers, sets of molecular parameters were computed. Fourty-four parameters allow us to reproduce the 2000 experimental wavenumbers with a rms lower than 9 × 10−5 cm−1.

Experimental rovibrational populations of CO up to ν = 40 from doppler-limited fourier spectra of the sequences Δν = 1, 2 and 3 emitted by a laser type source

Abstract High-resolution emission Fourier spectra have been recorded from a CON 2 HeO 2 mixture excited by dc discharge and cooled by liquid nitrogen. Intensities of all the observed rovibrational lines belonging to sequences Δν = 1, 2 and 3 of 12 C 16 O and 13 C 16 O, and Δν = 1 of 12 C 16 O, have been measured. The data treatment is described. Accurate determination of the rotational distribution and of the vibrational populations of the three isotopic species is performed. The Δν = 2 and 3 vibrational radiative transition probabilities, versus the Δν = 1 ones, are also given, up to ν = 40.

HNSi; ν1 emission band by high resolution Fourier transform spectroscopy

The emission spectrum of the fundamental vibration–rotation ν1 band (NH stretch) of iminosilicon HNSi has been observed near 2.7 μm by high resolution Fourier transform spectroscopy from a mixture of N2+SiH4 excited in a radio frequency discharge. This is the first spectroscopic observation of this molecule in the gas phase. Molecular constants σ, B, D, H are reported. Calculated microwave transitions which should be helpful for the investigation and the possible identification of HNSi in astrophysical sources are also given.

Analysis of the high-resolution spectrum of acetylene in the 2.4 μm region

Abstract The high-resolution Fourier transform spectrum of acetylene in the 2.4 μm region has been obtained at an apodized resolution of 0.0054 cm −1 . In the analysis of the ( ν 1 + ν 4 + ν 5 ) 2.0 ← ν 4 1 and ( ν 1 + 2 ν 5 ) 2.0 ← ν 5 1 hot bands occurring in this region, the vibrational and rotational l -type resonances have been explicitly taken into consideration. The spectral data have been fitted with residuals approaching the experimental accuracy and molecular parameters have been obtained for the bands investigated. The present studies have also shown that the assignments of the ( ν 1 + ν 4 + ν 5 )(Σ u − ) ← ν 4 (Π g ) and ( ν 1 + ν 4 + ν 5 )(Δ u ) ← ν 4 (Π g ) subbands reported by previous workers must be interchanged.

Vibrational luminescence of N2O excited by dc discharge: Rotation-vibration constants

Abstract High resolution measurements have been performed on 19 emission and absorption bands of the nitrous oxide molecule at 4.7 μm and 2.9 μm. Accurate values of the vibrational and rotational constants of 23 vibration levels were obtained.

Vibrational luminescence of CO2 excited by dc discharge: Rotational and vibrational molecular constants

Abstract High-resolution measurements have been performed on 33 emission bands of the carbon dioxide molecule from 4.2 to 4.7 μm. Accurate values of the vibrational and rotational constants of 39 vibration levels were obtained. Molecular constants were calculated from observed wavenumbers.

“Anomalous” rovibrational intensities in the Δv = 1 bands of SH (X2Π)

Abstract Reported here are the first intensity measurements of rovibrational transitions for Δv = 1 vibrational bands of the 2Π ground electronic state of SH. The observed relative intensities are strongly perturbed but are consistent with ab initio calculations of the electric dipole moment function, made by J. Senekowitsch, H.-J. Werner, P. Rosmus, and E.-A. Reinsch [J. Chem. Phys. 83, 4661–4667 (1985)] which, in relation to other diatomic hydrides, predict a very large value for the ratio of the permanent electric moment to its first derivative and, therefore, a large Herman-Wallis intensity perturbation. Also consistent with the ab initio calculations is our observation of analogous transitions of SH−, observed on the same spectrum, which display a “normal” intensity distribution.

Vibrational luminescence of N2O excited by dc discharge: Emission lines intensities and populations of rotational-vibrational levels

Abstract A SISAM spectrometer was used for studying the spontaneous emission of a gaseous mixture N 2 ON 2 excited by dc discharge in the 4.7 μm range. Populations of the rotation-vibration levels have been obtained from measurements of line intensities.

High Resolution Fourier Transform Spectroscopy Of N2O Discharge By Selective Polarization Modulation

A new method for the selective detection of paramagnetic molecules in high resolution Fourier spectroscopy is described. Essentially, it is founded on the circular polarization property of the Zeeman transitions in a longitudinal magnetic field. It is applied to the selective detection of the NO radical created in a N20 electrical discharge.