S. Kassi

Acetylene, 12C2H2: new CRDS data and global vibration-rotation analysis up to 8600 cm-1

The absorption spectrum of 12C2H2 has been recorded using cavity ringdown spectroscopy and analyzed in the ranges 6000 − 6356 cm−1 and 6667−7015 cm−1. Fourteen new bands have been identified and additional J-lines were assigned in 10 already known bands. These new data, together with the published vibration–rotation absorption lines of 12C2H2 accessing vibrational states up to 8600 cm−1 have been gathered in a database. The resulting set includes 12137 transitions involving 186 different k = l 4 + l 5 sub-states, with l i the angular momentum quantum number associated to the i degenerate bending vibration. These lines have been fitted simultaneously to spectroscopic parameters through J-dependent Hamiltonian matrices exploiting the vibrational polyad or cluster block-diagonalization, in terms of the pseudo-quantum numbers Nr = 5v 1 + 3v 2 + 5v 3 +v 4 +v 5 and Ns = v 1 + v 2 + v 3, also accounting for k and e/f parities and u/g symmetry. Modes 1 and 2 correspond to the symmetric CH and CC stretchings, mode 3 to the antisymmetric CH stretch, and modes 4 and 5 to the trans- and cis-degenerate bendings, respectively. The fit was successfully achieved, with a dimensionless standard deviation of 0.92, leading to the determination of 266 effective vibration-rotation parameters.

The absorption spectrum of water near 750 nm by CW-CRDS: contribution to the search of water dimer absorption

The absorption spectrum of natural water vapour around 750 nm has been recorded with a typical sensitivity of 3 x 10(-10) cm(-1) using a cw cavity ring down spectroscopy set up based on a Ti:sapphire laser. The 13 312.4-13 377.7 cm(-1) spectral interval was chosen as it corresponds to the region where water dimer absorption was recently measured (K. Pfeisticker et al., Science, 2003, 300, 2078-2080). The line parameters (wavenumber and intensity) of a total of 286 lines of water vapor were measured by a one by one fit of the lines to a Voigt profile. For the main water isotopologue, 276 lines were measured with line intensities as weak as 5 x 10(-29) cm molecule(-1)i.e. about 50 times smaller than the weakest H(2)16O line intensities included in the 2004 edition of the HITRAN database. On the basis of the predictions of Schwenke and Partridge, all but 16 lines could be assigned to different isotopologues of water (H(2)16O, H(2)18O, and HD16O) present in natural abundance in the sample. A total of 272 energy levels of H(2)16O were determined and rovibrationally assigned to 18 upper vibrational states. Half of them had not been reported previously. The importance of the additional absorbance resulting from the observation of many new weak lines is discussed in relation to the detection of water dimer absorption and compared to the absorbance predicted by Schwenke and Partridge. The quality of the line parameters of water monomer is shown to be of crucial importance to identify the absorbance of the water dimer in the considered region.

ROVIBRATIONAL LINE LISTS FOR NINE ISOTOPOLOGUES OF THE CO MOLECULE IN THE X 1Σ+ GROUND ELECTRONIC STATE

Extensive rovibrational line lists were computed for nine isotopologues of the CO molecule, namely, {sup 12}C{sup 16}O, {sup 12}C{sup 17}O, {sup 12}C{sup 18}O, {sup 13}C{sup 16}O, {sup 13}C{sup 17}O, {sup 13}C{sup 18}O, {sup 14}C{sup 16}O, {sup 14}C{sup 17}O, and {sup 14}C{sup 18}O in the ground electronic state with v ≤ 41, Δv ≤ 11, and J ≤ 150. The line intensity and position calculations were carried out using a newly determined piece-wise dipole moment function (DMF) in conjunction with the wavefunctions calculated from an experimentally determined potential energy function from Coxon and Hajigeorgiou. A direct-fit method that simultaneously fits all the reliable experimental rovibrational matrix elements has been used to construct the dipole moment function near equilibrium internuclear distance. In order to extend the amount and quality of input experimental parameters, new Cavity Ring Down Spectroscopy experiments were carried out to enable measurements of the lines in the 4-0 band with low uncertainty as well as the first measurements of lines in the 6-0 band. A new high-level ab initio DMF, derived from a finite field approach has been calculated to cover internuclear distances far from equilibrium. Accurate partition sums have been derived for temperatures up to 9000 K. In additionmorexa0» to air- and self-induced broadening and shift parameters, those induced by CO{sub 2} and H{sub 2} are now provided for planetary applications. A complete set of broadening and shift parameters was calculated based on sophisticated extrapolation of high-quality measured data. The line lists, which follow HITRAN formalism, are provided as supplementary material.«xa0less

Demonstration of cavity enhanced FTIR spectroscopy using a femtosecond laser absorption source

A proof of principle experiment was performed by recording the cavity enhanced absorption spectrum of the weak b-X transition of molecular oxygen in the atmosphere using a Ti:Sa femtosecond laser as an absorption source and a high resolution continuous scan Fourier transform interferometer. The cavity was mode matched and either continuously scanned or stabilized at the so-called magic point. An optimal rms noise equivalent absorption of 3x10(-7) cm(-1) Hz(-1/2) was reached in the latter case, corresponding to alpha(min)=3x10(-7) cm(-1).

A Microdrop Generator for the Calibration of a Water Vapor Isotope Ratio Spectrometer

Abstract A microdrop generator is described that produces water vapor with a known isotopic composition and volume mixing ratio for the calibration of a near-infrared diode laser water isotope ratio spectrometer. The spectrometer is designed to measure in situ the water vapor deuterium and oxygen (17O and 18O) isotope ratios from the low troposphere up to the lower stratosphere with a high temporal resolution, and is based on ultrasensitive optical-feedback cavity-enhanced absorption spectroscopy. To calibrate the spectrometer, a commercial microdrop generator (Microdrop GmbH) is used to inject water droplets of known size at a preset repetition frequency into a stream of dry nitrogen or synthetic air. Complete evaporation of the small droplets ensures that there is no isotopic fractionation between the liquid phase and the generated moist “air.” The water mixing ratio of the synthetic air is controlled by the repetition rate and gas flow. The current system spans a water mixing ratio range from about 10 ...

Cavity enhanced FTIR spectroscopy using a femto OPO absorption source

The ν1u2009+u2009ν3 band of 12C2H2 was recorded using a high resolution continuous scan Fourier transform interferometer fitted with a femto OPO absorption source. Various experimental schemes were successfully implemented, including multipass absorption in a cell and also in a supersonic expansion, and cavity enhanced absorption. An optimal rms noise equivalent absorption of 2.2u2009×u200910−9u2009cm−1u2009Hz−1/2 per spectral element was reached in the latter case, corresponding to αminu2009=u20091.5u2009×u200910−7u2009cm−1. Performances are illustrated and discussed.

Incoherent broad-band cavity-enhanced absorption spectroscopy for simultaneous trace measurements of NO2 and NO3 with a LED source

In the past decade, due to a growing awareness of the importance of air quality and air pollution control, many diagnostic tools and techniques have been developed to detect and quantify the concentration of pollutants such as NOx, SOx, CO, and CO2. We present here an Incoherent Broad-Band Cavity-Enhanced Spectroscopy (IBB-CEAS) set-up which uses a LED emitting around 625u2009nm for the simultaneous detection of NO2 and NO3. The LED light transmitted through a high-finesse optical cavity filled with a gas sample is detected by a low resolution spectrometer. After calibration of the spectrometer with a NO2 reference sample, a linear multicomponent fit analysis of the absorption spectra allows for simultaneous measurements of NO2 and NO3 concentrations in a flow of ambient air. The optimal averaging time is found to be on the order of 400u2009s and appears to be limited by the drift of the spectrometer. At this averaging time the smallest detectable absorption is 2×10−10xa0cm−1, which corresponds to detection limits of 600u2009pptv for NO2 and 2u2009pptv for NO3. This compact and low cost instrument is a promising diagnostic tool for air quality control in urban environments.

Optical feedback stabilized laser tuned by single-sideband modulation.

We report a subkilohertz-linewidth distributed-feedback diode laser that is optical-feedback locked to a highly stable V-shaped cavity with drift rates below 20 Hz/s. This source is continuously tunable over 1 THz around 1590 nm by selecting a cavity mode and using an innovative single-sideband modulation scheme, which allows for frequency shifting over up to 40 GHz with millihertz accuracy. This robust setup achieves high performance without advanced vibration isolation and will be a powerful tool for metrological applications, in particular a redetermination of the Boltzmann constant by molecular spectroscopy.

17O12C17O and 18O12C17O spectroscopy in the 1.6 μm region

Near infrared spectra of a carbon dioxide sample enriched with oxygen-17 have been recorded using a high-resolution continuous scan Fourier transform interferometer fitted with a femto OPO/Idler laser source. Cavity enhanced absorption has been achieved in a static gas cell allowing an optimal rms noise equivalent absorption of 1.2u2009×u200910−10u2009cm−1u2009Hz−1/2 per spectral element to be reached, corresponding to αminu2009=u200910−8u2009cm−1. Spectra were calibrated against acetylene reference line positions. Three bands in the 3ν1u2009+u2009ν3 tetrad in both 12C17O2 and 12C17O18O have been identified and rotationally analyzed, as well as some related hot bands, eight of which are newly reported and three with their analysis updated compared with a preliminary report (X. de Ghellinck d’Elseghem Vaernewijck et al., Chem. Phys. Lett. 514, 29 (2011)).