Measurements of surface loss probabilities of oxygen atoms on Simax glass, PET, Teflon, and Mica at room temperature are presented. The surface loss probability was measured by using a stationary afterglow double pulse discharge technique. The main discharge pulse created oxygen atoms by dissociation of O-2 molecules. The second (probe) discharge pulse excited existing atoms in the afterglow. The decay of the density of the oxygen atoms in volume was monitored by discharge induced emission spectroscopy of O lines and Ar actinometric lines. The rate of decay of oxygen atoms was used to determine their surface loss probability. The determined surface loss probabilities are: Simax (3.9 +/- 0.65) x 10(-3), PET (9.3 +/- 1.3) x 10(-4), Teflon (6.6 +/- 1.3) x 10(-4), and Mica (1.2 +/- 0.3) x 10(-3). (C) 2011 Elsevier Ltd. All rights reserved.

Continuous wave cavity ring-down spectroscopy using an electronically switched telecom distributed feedback laser module is demonstrated. By adding a compensation waveform current to the step-function switched laser current the laser wavelength stabilisation time is reduced to about 4 ms corresponding to a 200 Hz utmost ring-down transient repetition rate.

The absorption spectrum of the (1–0) band of the b1Σg+←a1Δg Noxon system near 1505 nm has been recorded by cw-CRDS in afterglow of a microwave discharge. The details of this method are presented along with spectroscopic data of 29 recorded lines of which 21 have been observed for the first time. The measured line positions are compared with positions calculated from rotational constants available in the literature. The density and the temperature of the generated singlet molecular oxygen O2(a1Δg) are presented.

New theoretical and experimental results on the acetylene-Ar van der Waals complex are presented and the literature is reviewed. New ab initio calculations at the MP2 level were performed using large basis sets with diffuse functions and taking into account the basis set superposition error. It was found that the structure of acetylene is not significantly altered by the complexation and that its vibrational frequencies are only slightly lowered. Finally, it was observed that the calculated properties of the complex (structure, vibrational spectrum, bond dissociation energy) are not sensitive to the structure imposed on acetylene. Experimentally, acetylene-Ar was produced in a supersonic expansion under experimental conditions corresponding to 9 K rotational temperature. Thanks to the performances of CW-CRDS detection, the K(a) = 0 <-- 1, 1 <-- 0, and 2 <-- 1 sub-bands of the nu(1) + nu(3) band could be recorded and resolved and most of their lines assigned. Upper-state rotational constants were fitted, however not including the upper K(a) = 2 state, which shows K-doubling the opposite of the expected. The Lorentzian width of most line profiles sets the mean lifetime to some 7.5 ns. Local perturbations affecting line positions and/or line widths are demonstrated. Additional series of lines tentatively attributed to acetylene-Ar are discussed.

A slit nozzle supersonic expansion containing C2H2 (246sccm) and N2O (355sccm) seeded into Ar (1260sccm) is investigated using CW cavity ring-down spectroscopy, in the 1.5μm range. The C2H2−N2O van der Waals complex is observed around the 2CH acetylenic band. Despite strong perturbations, 117 b-type lines are assigned. Their combined fit with published microwave data leads to new upper state and improved lower state rotational constants. The Lorentzian width of the assigned line profiles sets the mean lifetime to 1.6ns. The rotational temperature is estimated to be 15K from the comparison between observed and simulated spectra.

A supersonic expansion containing acetylene seeded into Ar and produced from a circular nozzle is investigated using CW/cavity ring down spectroscopy, in the 1.5 mu m range. The results, also involving experiments with pure acetylene and acetylene-He expansions, as well as slit nozzles, demonstrate that the denser central section in the expansion is slightly heated by the formation of acetylene aggregates, resulting into a dip in the monomer absorption line profiles. Acetylene-Ar aggregates are also formed at the edge of the circular nozzle expansion cone. (C) 2008 Elsevier B. V. All rights reserved.

Continuous wave (cw) distributed feedback (DFB) telecom diode lasers are increasingly being used as light sources in the near-IR regions of the spectrum for cavity ring-down spectroscopy (CRDS). They are compact, operate economically at room temperature, are able to generate suitable narrowband tunable coherent radiation on a single longitudinal mode and are compatible with a variety of optical components, including fibre-optic devices. The very high sensitivities enabling to measure weak absorption with cw CRDS plus the quantitative nature of the absorption measurements are enabling an expanding range of applications of cw CRDS in molecular spectroscopy, atmospheric chemistry, plasma and medical diagnosis.

The design of a new apparatus, named FANTASIO, for studying jet-cooled molecules is described. It includes, around the same supersonic expansion cell, a high resolution Fourier transform spectrometer with single or multipass optics, a tunable diode laser spectrometer with optional cavity ring-down facilities, and a quadrupole mass spectrometer. Performance and operational procedures are illustrated.

In spectra of jet-cooled C2H2 recorded with an FTIR spectrometer, the ν5, ν4+ν5, ν3 and ν2+ν4+ν5 bands all exhibit an intensity distribution corresponding to ∼6K for rotation, with no evidence of nuclear spin conversion. Spectra of C2H2 isolated in solid p-H2 show no evidence of rotation of C2H2. The strong interaction between ν3 and ν2+ν4+ν5 in the gas phase is diminished in solid p-H2. Lines associated with dimer, trimer and tetramer of C2H2 are identified. Spectral features characteristic of solid state acetylene are observed under jet-cooled conditions.

We have used CW cavity-ring-down-spectroscopy around 1.5 mu m to probe a free supersonic expansion of mixed acetylene and Argon. The high resolution spectrum of the 2CH band in the (C2H2)-C-12-Ar van der Waals complex was recorded, at a rotational temperature of about 15 K. Upper state spectroscopic constants are provided from the fit of the 44 assigned vibration-rotation lines in the K-a = 0 <- 1 and 1 <- 0 sub-bands to a conventional Watsonian. (C) 2007 Elsevier B.V. All rights reserved.

We have used a Fourier transform intracavity laser absorption spectrometer to measure the absolute intensity of lines in the ν1+3ν3 band of 12C2H2 at 12675cm−1. Under optimal conditions the agreement is found to be within 5% of reference values measured by conventional Fourier transform spectroscopy [F. Herregodts et al., Mol. Phys., 101 (2003) 3427]. The absolute intensity of 21 weaker lines not experimentally investigated in the latter work, is listed. Various tests of the instrumental method are presented, also demonstrating its ability to determine pressure self-broadening coefficients.

The recombination of H+3 ions with electrons has been studied in afterglow plasma in three different experiments. In two experiments, using the Variable Temperature Stationary Afterglow (VT-AISA) and the Variable Temperature Flowing Afterglow (VT-FALP) techniques, a decay of the electron number density was measured by an electrostatic Langmuir probe to determine the recombination rate coefficient. In the third experiment a near infrared Cavity Ring-Down Absorption Spectrometer (CRDS) was used to monitor the decay of the H+3 (v = 0) ion density during the afterglow. Measurements were carried out in helium buffer gas with small admixtures of argon and hydrogen at total pressures ranging from 150 up to 1200 Pa and at buffer gas temperatures ranging from 100 up to 330 K. In the experiments the partial number density of hydrogen was varied from 5 × 1010 up to 1 × 1016 cm−3 and for this broad range of hydrogen number densities effective recombination rate coefficients were obtained, which varied over three orders of magnitude from 2 × 10−9 cm3s−1 at [H2] = 5 × 1010 cm−3 up to 3 × 10−6 cm3s−1 at [H2] = 1 × 1016 cm−3. Using our experimental results we discuss possible mechanisms of recombination in hydrogen plasma in a very broad range of several parameters: buffer gas pressure, temperature, electron number density, hydrogen number density and internal excitation of recombining ions.

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.

We report a study of the recombination of H3+ (v = 0) ions with thermal electrons at 330 and 100 K. A near infrared cavity ring-down absorption spectrometer (CRDS) working on the v2 = 3 ← 0 transition of H3+ (λ = 1382 nm) has been used to monitor the H3+ (v = 0) ion number density in decaying afterglow plasma. The plasma was created in helium gas with small admixtures of argon and hydrogen by pulses of microwaves. The measurements were carried out for hydrogen number densities ranging from 1013 up to 1016 cm−3. The total pressure in the discharge tube was 4–10 mbar. The temperature of the recombining ions was determined from the Doppler broadening of absorption lines. The obtained effective recombination rate coefficients are α (H3+ (v = 0)) = (0.8 ± 0.3) × 10−7 cm3s−1 and α(H3+ (v = 0)) = (2.3 ± 1.1) × 10−7 cm3s−1 at 330 and 100 K, respectively. The influence of the formation of H5+ at higher pressures and lower temperature is also discussed.

The absorption spectrum of 13CO2 has been recorded by cw-cavity ringdown spectroscopy with a new set up based on fibered DFB lasers. By using a series of 31 DFB lasers, the spectrum of carbon dioxide could be recorded in the 6130–6750cm−1 region with a typical sensitivity of 5×10−10cm−1. The spectrum has also been recorded between 4400 and 8500cm−1 with a Fourier transform spectrometer associated with a multi-pass cell (maximum path length of 105m). The new observations obtained both by FTS and CRDS represent a significant extension of the available data. For instance, more than 4000 line positions were measured and assigned in the CRDS spectrum while only 232 line positions are listed in the HITRAN database. Altogether, the band by band analysis has led to the determination of the rovibrational parameters of 65, 7, and 24 bands for the 13C16O2, 16O13C17O, and 16O13C18O isotopomers, respectively. As some observed line positions show significant deviations from the predictions of the effective Hamiltonian model, the new observed line positions were gathered with the data available in the literature to refine the set of effective Hamiltonian parameters of the 13C16O2 isotopic species. The refined set of 96 effective Hamiltonian parameters reproduces more than 14650 line positions of 13C16O2 with an RMS=0.002cm−1. A detailed comparison with the line positions retrieved from Venus spectra and the line list provided by HITRAN is also presented and discussed.

The dissociation efficiency of a pulsed RF discharge (with duty cycle 1:1 and discharge duration 0.2, 1, 5, and 20 ms) in oxygen at pressures from 1 to 5 torr and effective discharge currents from 50 to 210 mA has been studied. For monitoring of the atomic oxygen density the method of actinometry has been used. In order to evaluate the absolute dissociation degree, a numerical model has been developed and actinometric coefficients were calculated. Maximal degree of the dissociation reached value of 0.05. A saturation of the dissociation degree at higher pressures was observed and discussed.

The absorption spectrum of carbon dioxide in natural isotopic abundance has been recorded by CW-cavity ringdown spectroscopy with a setup based on fibered DFB lasers. By using a series of 31 DFB lasers, the CO2 spectrum could be recorded in the 6132–6747cm−1 region with a typical sensitivity of 5×10−10cm−1. More than 3300 line positions were measured and assigned to the 12C16O2 species while only 1159 (generally calculated) line positions are provided by the HITRAN database. Altogether, the band-by-band analysis has led to the determination of the rovibrational parameters of 53, 5, and 9 bands for the 12C16O2, 16O12C17O, and 16O12C18O isotopologues, respectively. For the three studied isotopologues, the majority of the observed line positions show an agreement close to the experimental uncertainty (3×10−3cm−1) with the predictions of their respective effective Hamiltonian models. Maximum deviations of the order of 0.03, 0.05, and 0.04cm−1 were, however, evidenced for 12C16O2, 16O12C17O, and 16O12C18O, respectively. As some observed line positions show significant deviations from the predictions of the effective Hamiltonian model and as the observed data set has been recently enlarged by newly reported measurements, the observed line positions were gathered with all the data available in the literature in order to refine the set of effective Hamiltonian parameters of the 12C16O2 isotopic species. The refined set of 130 effective Hamiltonian parameters reproduces more than 29000 observed line positions of 12C16O2 with an RMS=0.002cm−1. The comparison of our line positions values with those published earlier and with the line list provided by HITRAN is discussed.

Two techniques allowing us to measure the probability for the non-relaxation of metastable atoms impinging on glass surfaces are presented. In the first one, the radial distribution of Ar*(P-3(2)) metastable atoms in the proximity of the glass wall is determined by a resonant absorption technique in the afterglow of a low pressure (8.5 Pa) argon discharge. The comparison of the experimental density profile with model profiles predicted by a simple model, permits the determination of an upper limit, R less than or equal to, 0.45, for the non-relaxation probability. In the second experiment, the Doppler-shifted laser-induced fluorescence technique is used to deduce the velocity distribution function of Ar*(P-3(2)) metastable atoms in the vicinity of a Pyrex wall in very low pressure (0.09-0.5 Pa) argon plasmas. The non-relaxation probability is deduced from the ratio of the flux of metastable atoms having their radial velocity oriented towards the cell axis to the flux of those with their radial velocity oriented towards the wall. This latter technique is much more precise and gives a value of R = 0.28 +/- 0.05 for the non-relaxation probability. It is also shown that metastable atoms moving away from the surface have somehow been accommodated to the surface and acquired a velocity distribution corresponding to the wall temperature.

The surface recombination probability of oxygen atoms as a function of wall temperature is studied by using a double pulse discharge technique. The main discharge pulse dissociates molecular oxygen and the second pulse, shorter than the main one, excites atoms during the stationary afterglow. The recombination probability is determined from the atomic oxygen density decay during the stationary afterglow of the main pulse (MP). The oxygen atoms are detected by time-resolved optical emission spectroscopy. In order to correlate the oxygen emission lines with the oxygen atom density, argon is used as an actinometer. To scan the whole afterglow of the main discharge pulse, the delay of the probe pulse is uniformly increased in every period following the MP. The evolution of the relative 0 atom density is deduced from the 0 emission lines at 777 and 844 nm and from the Ar actinometry line at 750 nm. The wall recombination probability gamma on a Pyrex surface ranges from 4.0 x 10(-4) to 1.6 x 10(-2) for wall temperatures from 77 to 460 K.

The absorption spectrum of natural water vapour around 1.5μm has been recorded with a typical sensitivity of 5×10−10cm−1 by using a CW-cavity ring down spectroscopy set up based on fibred DFB lasers. A series of 31 DFB lasers has allowed a full coverage of the 6130.8–6748.5cm−1 (1.63–1.48μm) region corresponding to the H transparency band of the atmosphere. The line parameters (wavenumber and intensity) of a total of 5190 lines, including 4247 lines of water vapor, were derived by a one by one fit of the lines to a Voigt profile. Different isotopologues of water (H216O, H218O, H217O, and HD16O) present in natural abundance in the sample contribute to the spectrum. For the main isotopologue, H216O, 2130 lines were measured with line intensities as weak as 10−29cm/molecule while only 926 lines (including a proportion of 30% inaccurate calculated lines) with a minimum intensity of 3×10−27cm/molecule are provided by the HITRAN and GEISA databases. Our comparison in the whole 5750–7965cm−1 region, has also evidenced that an error in the process of conversion of the intensity units from cm−2/atm to cm−1/(molecule×cm−2) at 296K, has led to H216O line intensities values listed in the HITRAN-2000 database, systematically 8 % below the original FTS values. The rovibrational assignment was performed on the basis of the ab initio calculations by Schwenke and Partridge with a subsequent refinement and validation using the Ritz combination principle together with all previously measured water transitions relevant to this study. This procedure allowed determining 172, 139, 71, and 115 new energy levels for the H216O, H218O, H217O, and HD16O isotopologues, respectively. The results are compared with the available databases and discussed in regard of previous investigations by Fourier transform spectroscopy. The spectrum analysis has showed that most of the transitions which cannot be assigned to water are very weak and are due to impurities such as carbon dioxide and ammonia, leaving only about 3% of the observed transitions unassigned. The interest of a detailed knowledge of water absorption for trace detectors developed in the 1.5μm range is underlined: for instance HDO contributes significantly to the considered spectrum while no HDO line parameters are provided by the HITRAN database.