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9 pags., 5 figs., In this work several lines of the v3 fundamental band of the CH3 radical have been detected in a refrigerated hollow cathode discharge multipass cell filled with CH4, by using a discharge and laser amplitude double modulation technique, with a difference frequency laser spectrometer and a double phase sensitive detection. Bands of the precursor CH4 and of C2H4 and C2H6 produced in the discharge have been observed too. By Doppler broadening and absorption variations, the increase of temperature with the establishment of the discharge has been tested. It is only ∼15°C. Nevertheless, a very high sensitivity in transmittance variations with temperature is achieved for transitions from highly excited levels of stable species. The method proposed can be very useful for the assignment of very weak bands. © 1994 American Institute of Physics., This work was made with the financial support of the Spanish CICYT (Projects Nos. PB89-0041 and PB91-0128).

4 p.: gráf., We report the first experimental observation of homonuclear propensity in collisional relaxation of a polyatomic molecule. A pump-probe stimulated Raman setup is used to pump population to a single rotational level of the v2 = 1 vibrationally excited state in 13C12CD2 and then monitor the redistribution of the rotational population that has taken place after a fixed delay. The Q-branch of the 2ν2–ν2 band shows a pattern of intensity alternation between the even and the odd rotational components, with the greater intensities always corresponding to the rotational levels with the same parity as the one where all the population was initially deposited. The effect can be explained by the existence of a propensity rule that favors collisional relaxation between rovibrational levels of the same parity. © 2011 American Institute of Physics., Funding received from the Spanish Ministry of Science and Innovation through research Grant No. FIS2009-08069; support from CONSOLIDER-INGENIO 2010 Program CSD2009-00038

Infrared and Raman spectra of dideuterated acetylene containing one 13C atom, 13C12CD2, have been recorded and analysed to obtain detailed information on the fundamental 2 band and associated combination and hot bands. Infrared spectra were recorded at 4103cm1 resolution in the region 11502900cm1, which contains combination and hot bands from the ground and the bending v4¼1 and v5¼1 states. The Q-branches of the 2 fundamental and associated hot bands (2þ44, 2þ55, 2þ2424, 2þ2525 and 2þ4þ5(4þ5)) were recorded using inverse Raman spectroscopy, with an instrumental resolution of about 3103cm1. In addition, the observation of the 222 Raman band was carried out populating the v2¼1 state by stimulated Raman pumping. In total, 11 Raman and 9 infrared bands were analysed, involving all the l-vibrational components of the excited stretchingbending manifolds up to vt¼v4þv5¼2. A simultaneous analysis of all infrared and Raman assigned transitions has been performed on the basis of a theoretical model which takes into account the rotation and vibration l-type resonances within each vibrational manifold and the DarlingDennison anharmonic resonance between the 2þ24 and 2þ25 states. The parameters obtained reproduce the assigned transition wavenumbers with a standard deviation of the same order of magnitude as the experimental uncertainty.

Wavenumbers and relative peak heights of 62 peaks observed in the high-resolution “quasi-continuous wave Stimulated Raman Scattering” (q-cw SRS) spectrum of the 12CH4 molecule are reported for the first time. These peaks are assigned mainly to transitions with J values between 10 and 17 of the Q branch of ν1 and ν2 + ν4 bands. A comparison with the predictions of some theoretical models and some available IR data is made.

We report a stimulated Raman spectrum of the Q branch of the ν3 band of ethane recorded with a resolution of about 0.0055 cm−1 and an absolute wave‐number accuracy of the order of 0.001 cm−1. This spectrum is analyzed in terms of a vibrational–torsional coupling Hamiltonian that allows for the calculation of the observed wave numbers within the experimental uncertainty. The following spectroscopic parameters (in cm−1) have been obtained: ν30=994.1108(10), B3A1s−B0=−0.006 165(3), B3E3d−B0=−0.006 170(2), B3E3s−B0 =−0.006 184(2), B3A3d−B0=−0.006 257(2), A3A1s−A0=−0.003 037(15), A3E3d−A0 =−0.003 040(12), A3E3s−A0=−0.003 054(12), and A3A3d−A0=−0.003 065(12). A strong dependence of the threefold torsional potential barrier with respect to the q3 normal mode, ∂V3/∂q3=−275.9±1.4 cm−1, is deduced from the present analysis.

The high-resolution stimulated Raman spectrum of F2 has been recorded with a quasi cw technique. Q branches of the fundamental and first hot band have been fully resolved. Forty-one transitions of the Q branch of the fundamental up to J = 43 have been measured, in addition to 21 transitions of the O and S branches of this band. Twenty-one transitions of the Q branch of the first hot band up to J = 27 have also been measured. From the analysis of these data a more accurate set of molecular parameters for the v = 0, v = 1, and v = 2 states of this molecule has been derived. From our data and some previous fluorescence data a new set of equilibrium parameters is also proposed.

Wavenumbers and relative peak heights of 62 peaks observed in the high-resolution “quasi-continuous wave Stimulated Raman Scattering” (q-cw SRS) spectrum of the 12CH4 molecule are reported for the first time. These peaks are assigned mainly to transitions with J values between 10 and 17 of the Q branch of ν1 and ν2 + ν4 bands. A comparison with the predictions of some theoretical models and some available IR data is made.

A new set of wavenumbers for the Stimulated Raman Spectrum (SRS) of the ν1 band of 12CH4 is presented using the Infrared (IR) absorption spectrum of the P10 component of ν3 of the same molecule as a wavenumbers standard. An estimation of the Stark shift due to the pump laser field is experimentally deduced what allows to extrapolate the measured wavenumbers to zero field amplitude. A careful discussion about the main possible error sources and how to cope with them is also included.The absolute accuracy of the wavenumbers set presented here is believed to be at least one order of magnitude better as compared with previous measurement.

9 pages, 7 figures.-- Printed version published Sep 2009., An anomalous lineshape of stimulated Raman spectra obtained from the region very close to the nozzle of supersonic pulsed expansions of nitrogen is presented. High-resolution Raman spectra of the Q branch of the fundamental vibration mode of N2 have been recorded from two different nitrogen expansions at T0 = 295 K and P0 = 1.5-3.5 bar, the lasers crossing the jet axis in the range z/D = 0.25-1.25, where D is the effective nozzle diameter. The combination of Doppler shifts and strong gradients of density and temperature in the near-nozzle region yield an inhomogeneous broadening and a double peak structure of the recorded Raman line profiles. The comparison of the experimental results with the simulation of the Raman spectrum from this region provides valuable information about the near-nozzle flow field. The lineshape described here is different from another reported previously in the literature, which is based on a depletion of the density of free molecules on the axis due to condensation., A. Ramos acknowledges CSIC for an I3P grant. This work has been funded by the DGI (MEC) of Spain under grants ENE 2006-14577-C04-03/FTN, FIS 2004-02558, FIS 2005-02029, and FIS 2007-61686.

An intracavity laser absorption installation in which the emission of the dye is analyzed with a commercial FT spectrometer is described. The pumping of the dye laser is modulated synchronously with the sampling of the interferogram in order to control the generation time of the laser. A total of 318 line positions belonging to some very weak bands of the B - X transition of natural chlorine and 37 Cl 2 in the region 16 000–16 470 cm −1 are reported for the first time.

The Energy-Corrected Sudden (ECS) model has been widely developed to calculate rovibrational Raman linewidths as well as the overlap between lines through the off-diagonal elements of the relaxation matrix. The accuracy of the results depends on the precision of the input data on which the ECS parameters are fitted. Starting from recent experimental and theoretical data for nitrogen (N2) Q-branch perturbed by hydrogen from 77 to 580 K, we have determined the ECS parameters for this molecular system and calculated systematically the N2H2 line broadening coefficients for J = 0 to 20 up to 2000 K, which will be useful for combustion diagnostics purposes. Copyright © 2008 John Wiley & Sons, Ltd.

In this work we present a theoretical and experimental study of the acetylene‐hydrogen system. An ab initio potential surface has been obtained by ab initio quantum chemistry methods. This 4‐dimensional potential is further used to compute pressure broadening coefficients of C2H2 isotropic Raman Q lines on a large scale of temperatures within both the close‐clouping approach and the coupled‐states approximation. Experimental data for the acetylene V2 Raman lines broadened by molecular hydrogen are obtained using stimulated Raman spectroscopy. Comparisons of theoretical values with experimental data measured at 143 K are promising. In addition, we discerned means of improving computational efficiency.

In this work we present new experimental and theoretical values for the line broadening coefficients of the Q‐branch Raman lines of autoperturbed N2. For the experimental determination of the coefficients, high resolution stimulated Raman loss spectra of the Q‐branch of N2 at different pressures were obtained at 77, 194 and 298 K. Simultaneously, we carried out Close‐Coupling calculations at 77, 113, 194 K, and Coupled‐states calculations at 298 K rendering a set of theoretical line broadening coefficients that could be directly compared to those obtained from our measurements and from available data in the literature. We observe a good agreement between theoretical and experimental values.

International audience; In this work we present a theoretical and experimental study of the acetylene–hydrogen system. A potential surface considering rigid monomers has been obtained by ab initio quantum chemistry methods. This 4-dimensional potential is further employed to compute, using the close-coupling approach and the coupled-states approximation, pressure broadening coefficients of C2H2 isotropic Raman Q lines over a temperature range of 77 to 2000 K. Experimental data for the acetyleneν2 Raman lines broadened by molecular hydrogen are obtained using stimulated Raman spectroscopy. The comparison of theoretical values with experimental data at 143 K is promising. Approximations to increase the computational efficiency are proposed.

Laser evaporation of solid Ge targets is used to grow Ge films onto glass and carbon-coated substrates. Rotation of the target yields the formation of good-quality amorphous films at 0.3-0.6 nm s-1 rates. Comparison of their Raman spectra to those of films grown by sputtering shows no significant differences. The spatial distribution of the deposited material is studied by means of optical microdensitometry. It is found to depend on the experimental geometry and different cosnθ laws (θ is the angle from the target normal) are found to fit the experimental results. © 1990., This work is partially supported by CICYT MAT88-0437 (Spain).

The high-resolution stimulated Raman spectrum of the ν1 band of GeD4 with natural isotopic abundance germanium has been recorded. It has been analyzed as part of the ν1/ν3 stretching dyad. The ν1 and ν3 band centers have been deduced for all the isotopologues. Copyright © 2006 John Wiley & Sons, Ltd.

International audience; In this work the authors present an experimental and theoretical study about the Q-branch lines' broadening coefficients of N2 perturbed by H2. Experimental values for these parameters have been obtained at 440 and 580 K, and quantum calculations have been performed using a new ab initio potential energy surface, obtained by quantum chemistry methods. The results of these calculations are compared to experimental data obtained previously at 77 and 298 K [L. Gomez et al., Mol. Phys. 104, 1869 (2006)] and to the present measurements. A satisfactory agreement is obtained for the whole range of temperatures used in the experiments.

11 pags.; 4 figs.; 9 tabs., © 2015 AIP Publishing LLC. Infrared and Raman spectra of mono 13C fully deuterated acetylene, 13C12CD2, have been recorded and analysed to obtain detailed information on the C—D stretching fundamentals and associated combination, overtone, and hot bands. Infrared spectra were recorded at an instrumental resolution ranging between 0.006 and 0.01 cm−1 in the region 1800–7800 cm−1. Sixty new bands involving the ν 1 and ν 3 C—D stretching modes also associated with the ν 4 and ν 5 bending vibrations have been observed and analysed. In total, 5881 transitions have been assigned in the investigated spectral region. In addition, the Q branch of the ν 1 fundamental was recorded using inverse Raman spectroscopy, with an instrumental resolution of about 0.003 cm−1. The transitions relative to each stretching mode, i.e., the fundamental band, its first overtone, and associated hot and combination bands involving bending states with υ 4 + υ 5 up to 2 were fitted simultaneously. The usual Hamiltonian appropriate to a linear molecule, including vibration and rotation l-type and the Darling–Dennison interaction between υ 4 = 2 and υ 5 = 2 levels associated with the stretching states, was adopted for the analysis. The standard deviation for each global fit is ≤0.0004 cm−1, of the same order of magnitude of the measurement precision. Slightly improved parameters for the bending and the ν 2 manifold have been also determined. Precise values of spectroscopic parameters deperturbed from the resonance interactions have been obtained. They provide quantitative information on the anharmonic character of the potential energy surface, which can be useful, in addition to those reported in the literature, for the determination of a general anharmonic force field for the molecule. Finally, the obtained values of the Darling–Dennison constants can be valuable for understanding energy flows between independent vibrations., The Bologna authors acknowledge the Università di Bologna and the financial support of the Ministero dell’ Istruzione dell’Università e della Ricerca (PRIN 2012 “Spettroscopia e Tecniche computazionali per la ricerca Astrofisica, atmosferica e Radioastronomica”). D.B. and R.Z.M. acknowledge the financial support of the Ministry of Economy and Competitiveness through Research Grant No. FIS2012-38175.

9 p.Special Issue: Nineteenth Colloquium on High Resolution Molecular Spectroscopy, Salamanca 11–16 September 2005, The v2, v5 and 2v 6 regions of 34SF6 have been studied by stimulated Raman spectroscopy. We used an isotopically pure sample of 34SF6. A detailed analysis of the v2 and v5 fundamentals has been performed with the HTDS program suite (http://www.u-bourgogne.fr/LPUB/hTDS.html) dedicated to octahedral XY6 molecules. We also present a preliminary analysis of the 2v 6 band for both 32SF6 and 34SF6. Finally, we give the 32S-34S isotopic shifts for all the SF6 fundamentals.

The ν1 region of 32SF6 and 34SF6 has been studied by stimulated Raman spectroscopy. For both isotopomers, a detailed analysis has been performed. Several hot bands (ν1+ν6-ν6, ν1+2ν 6-2ν6, ν1+ν5-ν 5) have been taken into account to calculate synthetic spectra that satisfactorily reproduce the experimental data. These results, together with the previous studies of the other fundamental bands have allowed us to determine the equilibrium bond length of sulfur hexafluoride as r e=1.5560(1) Å, in very good agreement with recent ab initio calculations. The 2ν1-ν1 band has also been studied for both isotopomers by Raman-Raman double resonance spectroscopy and the resulting spectra have been analyzed. In this case, a striking difference is observed between the two isotopomers, since the 2ν1-ν 1 band of 34SF6 appears to have a very narrow structure that could not be rotationally resolved under the present experimental conditions. All analyses have been performed thanks to the HTDS program suite (http://www.u-bourgogne.fr/LPUB/hTDS.html) dedicated to octahedral XY6 molecules. © 2004 Elsevier Inc. All rights reserved., Financial support of the Ministry of Science and Technology under the project REN2002-01618.

The Q branch of the 2ν2 → ν2 band of 13C2D2 has been recorded with an instrumental resolution of about 0.003cm-1 using inverse Raman spectroscopy combined with stimulated Raman pumping in order to populate the ν 2=1 state. A weak local perturbation evident in the spectrum has been attributed to the effect of an anharmonic resonance between the ν 2=2 and ν3=ν4=ν5=1 Σg + states. To study this interaction, the components of the latter vibrational manifold (Σg +, Σg - and Δg), together with all the bending states up to (ν4 +ν5)=2 associated with ν3=1, have been characterized through the analysis of their infrared spectra. Both cold and hot bands from states thermally populated at room temperature, ν4, ν5, 2ν4, 2ν5 and ν4 + ν5, have been recorded in the region between 2300 and 3000cm-1 at an effective resolution of about 0.009cm-1. A simultaneous analysis of all the assigned transitions has been performed on the basis of a theoretical model which takes into account the rotational and vibrational ℓ-type resonances within each vibrational manifold, the Darling-Dennison anharmonic resonance between the ν3 + 2ν4 and ν3 + 2ν5 states, and the anharmonic interaction between the 2ν2 and ν3 + ν4 + ν5 states.

The sections in this article are Introduction Experimental Quasi-CW SRS Spectrometer Probe Laser Pump Laser Data Acquisition and Calibration Applications Diatomic Molecules Nitrogen Oxygen Hydrogen and Deuterium Fluorine and Chlorine Carbon and Nitrogen Monoxides Linear Molecules Carbon Dioxide Acetylene Other Linear Molecules Spherical Top Molecules Methane Other Spherical Top Molecules Symmetric Top Molecules Asymmetric Top Molecules Photoacoustic SRS Acknowledgements

An analysis of the ν17-ν4 difference bands near 800 cm-1 of two isotopic species, 10B2H6 and 11B2H6, of diborane has been carried out using infrared spectra recorded with a resolution of ca. 0.003 cm-1. In addition, the ν17 band of 10B2H6 has been recorded and assigned. Since this band in 11B2H6 had already been studied, it was possible to derive precise energy levels and Hamiltonian constants for the 41 vibrational states of both isotopic species. © 2000 Academic Press. All rights reserved., Spanish DGESIC Project PB97-1196.Alexander von Humboldt Foundation for a Humboldt Gay-Lussac award

The infrared bands line-mixing effects of methane perturbed by nitrogen were discussed at different pressures. The spectral shapes of the ν2, ν4 and ν3 bands were compared at room temperature while the ν3 region was employed for the investigation of thermal effects. The effects of collisions in the ν4 region's spectra were calculated at the room temperature. The Coriolis coupling between ν2 and ν4 vibrational states resulted in the failure of evolution modeling with increasing pressure of absorption.© 2000 American Institute of Physics

The Raman spectrum of cyanogen 13 C 2 14 N 2 has been investigated at nearly Doppler resolution by means of a stimulated Raman technique. The regions around the bandheads of the ν 1 (2260 cm −1 ) and ν 2 (835 cm −1 ) vibrations have been recorded. Besides the fundamentals, hot bands arising from v 5 = 1–3 and v 4 = 1 have been observed. A number of strong perturbations have been detected. The spectra have been analyzed and rotational constants for the excited states have been obtained. Computer simulations of the Raman contours have been carried out as a test of the assignments. A few weak Δ J = −2 lines have also been observed in the ν 1 region.

Line mixing effects are studied in the v3 band of CH4 perturbed by Ar and He at room temperature. Experiments have been made in the 2800-3200 cm-1 spectral region using four different setups. They cover a wide range of total densities, including low (0.25-2 atm), medium (25-100 atm), and high (200-1000 atm) pressure conditions. Analysis of the spectra demonstrates that the spectral shapes (of the band, the Q branch, the P and R manifolds,...) are significantly influenced by line mixing. The theoretical approach proposed in the preceding paper is used in order to model and analyze these effects. As done previously, semiclassical state-to-state rates are used together with a few empirical constants. Comparisons between measurements and spectra computed with and without the inclusion of line mixing are made. They prove the quality of the approach which satisfactorily accounts for the effects of pressure and of rotational quantum numbers on the spectral shape. It is shown that collisions with He and Ar lead to different line-coupling schemes (e.g., more coupling within the branches and less between branches) and hence to different shapes. The influence of line coupling between different branches and manifolds is evidenced and studied using high pressure spectra and absorption in the band wings. © 1999 American Institute of Physics.

Line-mixing effects have been studied in the ν3 band of CH4 perturbed by N2 at room temperature. New measurements have been made and a model is proposed which is not, for the first time, strictly empirical. Three different experimental set ups have been used in order to measure absorption in the 2800-3200 cm-1 spectral region for total pressures in the 0.25-2 and 25-80 atm ranges. Analysis of the spectra demonstrates the significant influence of line mixing on the shape of the Q branch and of the P and R manifolds. A model is proposed which is based on state-to-state collisional transfer rates calculated from the intermolecular potential surface with a semiclassical approach. The line-coupling relaxation matrix is constructed from these data and two additional parameters which are fitted on measured absorption. Comparisons between measurements and spectra computed accounting for and neglecting line mixing are made. They prove the quality of the approach which satisfactory accounts for the effects of pressure and of rotational quantum numbers on the spectral shape under conditions where modifications introduced by line mixing are important. For high rotational quantum number lines, the main features induced by collisions are predicted but some discrepancies remain; the latter may be due to improper line-coupling elements but there is strong evidence that the use of inaccurate line broadening parameters also contributes to errors in calculated spectra. © 1999 American Institute of Physics.

The relaxation of the energy stored in the translational and rotational degrees of freedom of N2 and CH4 in the course of free jet expansions has been experimentally studied. Rotational temperatures along the expansion axis were obtained by means of stimulated Raman spectroscopy, and terminal flow velocities and translational temperatures were determined from supersonic beam time-of-flight measurements. From these measurements low-temperature cross sections for rotational relaxation have been estimated. The results are compared with data from other experiments, and the validity of simple relaxation models is discussed. © 1997 American Chemical Society, Funded by the DGICYT of Spain under Grants PB94-0108 and PB95-09178-03.

Two new double modulation techniques for infrared absorption spectroscopy of transient molecules are described. Both of them are based in the modulation in concentration of the unstable species and the modulation in amplitude of the laser radiation. One of the methods is specific for short lived transients; the first results obtained with it for the H{sub 3}{sup +} spectrum are given. The other one is more suitable for longer lived species; it has been applied to the study of the {nu}{sub 3} band of CH{sub 3} and vibrational excited states of methane.

High resolution stimulated Raman spectra of the Q branches in the regions of the v and v3 Raman active modes of ethane (12C2H6) have been recorded. A complete analysis of the v3 region in terms of a vibrational torsional coupling has been achieved. For the v region spectra at 300 K, 173 K (static) and 30 K (jet expansion) have been recorded. On the basis of the 30 K spectrum, a preliminar assignment of the stronglyperturbed spectra is presented. INTRODUCTION Ethane can be considered as one of the prototype molecules with periodic torsional potentials. Several highresolution infrared bands of ethanet5 have been analyzed by taking into account perturbative effects on the rovibrational levels due to the torsional motion6. To our knowledge just one high resolution (stimulated) Ramanspectrum of ethane around 2950 cm1 has been previously reported7. So far no assignment has been proposed for this spectrum. We have investigated the high resolution stimulated Raman spectra of ethane in the v and

Using an original double modulation set-up of an IR difference frequency laser spectrometer and a hollow cathode discharge cell with methane, in addition to a double phase sensitive detection method, it has been possible to distinguish between (nu) 3 band spectral lines of the CH3 radical and the much stronger lines belonging to the C-H stretching bands of the precursor and other stable species (C2H4, C2H6) that appear in the discharge. The method has proved to be very sensitive to detect population variations versus temperature of very weak transitions from highly excited levels of CH4 and other stable species. The temperature characterization of several neutral species involved in the hollow cathode discharge has been tested and remarkably low temperatures have been obtained.

The transition dipole moment of the ν3 band of the methyl radical has been measured for the first time. A new discharge laser amplitude double modulation method with a difference frequency laser spectrometer and a hollow cathode discharge cell has been used. The CH3 concentration has been estimated from the absorption decay when the discharge is turned off. The transition dipole moment is found to be μν3 = 0.029 ± 0.005 D. © 1994 American Chemical Society., Financial support of the Spanish DGICYT (Project PB91-0128).

We have recorded stimulated Raman spectra of the central region of the v1 band of ethylene, both in a jet at temperatures down to ≈25 K, and in a static cell at room temperature and at ≈173 K. The rotational temperatures of the jet are estimated by computer simulation of the observed spectra. Only Q branches are recorded in this experiment. A vib-rotational analysis is performed and improved values are obtained for the band origin and the rotational constants of the v1=1 state of this molecule. Some perturbations are found to affect the rotational levels of this state. © 1994 Elsevier B.V., Financial support from the Spanish DGICYT, Projects PB9 1-O 128 and PB90-0 123. International collaboration was sup- ported by a Cooperation Program between CSIC of Spain and CNR of Italy, and by the Integrated Action HA93-088 between the DGICYT (Spain) and the BMFT (Germany).

12 pages, 6 figures, 4 tables.- PACS nrs: 33.20.Sn, 33.15.Mt, 33.20.Fb, 33.40.+f, 33.20.Tp, 33.80.Wz., A new technique for the direct determination of state-to-state rotational energy transfer rate constants in the gas phase is presented. It is based on two sequential stimulated Raman processes: the first one prepares the sample in a single rotational state of an excited vibrational level, and the second one, using the high resolution quasi-continuous stimulated Raman-loss technique, monitors the transfer of population to other rotational states of the same vibrational level as a function of the delay between the pump and the probe stages. The technique is applied to the odd-J rotational states of v2 = 1 acetylene at 155 K. The experimental layout, data acquisition, retrieval procedures, and numerical treatment are described. The quantity and quality of the data are high enough to allow a direct determination of the state-to-state rate constant matrix from a fit of the experimental data, with the only conditions of detailed balance and of a closed number of states. The matrix obtained from this direct fit is also compared with those obtained using some common fitting and scaling laws., This work has been funded by the Spanish Ministry of Education and Science through research Grant No. FIS2005-02029.

Absorption spectra in the 16 100-16 320 cm-1 region have been recorded for gaseous CHD3 at room temperature with 0.12 cm -1 resolution using a Fourier transform intracavity laser absorption technique. Two bands belonging to the N = 6 polyad, 61 (6ν1) and 62 (5ν1 + 2ν5), were identified and a rotational analysis for 61 including transitions up to J = 13, verified by means of ground-state combination differences, is reported. Comparison with rotational contants obtained from photoacoustic laser spectra at 77 K is discussed. © 1992 American Institute of Physics., Research Project Nos. PB89-0041 and PB87-0273 of the Comision Interministerial de Ciencia y Tecnologia (CICYT).

9 pags., 3 figs., 5 tabs., We report a stimulated Raman spectrum of the Q branch of the ν3 band of ethane recorded with a resolution of about 0.0055 cm-1 and an absolute wave-number accuracy of the order of 0.001 cm-1. This spectrum is analyzed in terms of a vibrational-torsional coupling Hamiltonian that allows for the calculation of the observed wave numbers within the experimental uncertainty. The following spectroscopic parameters (in cm-1) have been obtained: ν3 0=994.1108(10), B3 A1s-B0=-0.006 165(3), B3 E3d-B0=-0.006 170(2), B 3 E3s-B0 =-0.006 184(2), B3 A3d-B0=-0.006 257(2), A3 A1s-A 0=-0.003 037(15), A3 E3d-A0 =-0.003 040(12), A3 E3s-A0=-0.003 054(12), and A 3 A3d-A0=-0.003 065(12). A strong dependence of the threefold torsional potential barrier with respect to the q3 normal mode, ∂V3/∂q3=-275.9±1.4 cm -1, is deduced from the present analysis. © 1992 American Institute of Physics., The Direccion General de Investigacion Cientlfica y Tecnica, DGICYT, of Spain is acknowledged for financial support.

During the process of metal welding by continuos CO2 laser, a plasma of the metallic elements is formed. In order to improve the procedure it is necesary to characteryze this plasma. We have carried out spectroscopic measurement of both temperature and electronic density. Our target was iron, and only iron lines could be identified in all our experiments. So, we were forced to use only iron lines for the plasma diagnostic. Our results show the distribution, along more of 20 mm from the target surface, of a plasma which has at its maximum a temperature of 6300 K and an electronic density of 9x1016 cm-3.

It is well known that the metallic plasmas observed in laser welding play an important role in energy transfert during laser materials processing. They are critical to understanding energy transport to the workpiece. This paper reports an experimental investigation characterizing the plasma using visible emission -spectroscopy. These experiments provided the electron density and temperature distributions (~1017 cm-3 and 6000-7000 °K). The experimental data are then used to determine laser attenuation and refraction as the beam propagate through the plasma column. These results are compared with direct absorption measurements where an integrating spere has been used, and with a numerical simulation. It was observed that the absorption coefficient is closely correlated to the spatial and temporal behaviour of the plasma and the effect of refraction is of primary importance for laser processing when using other gases than helium at high laser intensity.

The absorption coefficient of the C02 laser light has been measured when metallic target of steel (35 NCD 16) and pure iron are irradiated with laser intensities varying from i03 to lO7Watt/cm 2 with helium gas shielding. The diagnostic used consists of an integrating sphere which collects all the laser light reflected by the target. This set-up allows a temporal resolution of this measurement of about 0. 1 ms. As the laser intensity increases, a clear correlation between the time-dependance of the increase of absorption and of the appearance of the plasma luminosity is evidenced. For higher intensities, when a keyhole regime is reached, this correlation disappears and the absorption reaches 95 %. This very high level of absorption is interpreted as a result of the geometrical trapping of the laser light inside the keyhole and a low contribution of plasma plume absorption to this process.

The construction of a spectrometer for high-resolution stimulated Raman spectroscopy is reported and the accuracy of wavenumber determination achievable is discussed. A Doppler-limited spectrum of the C[BOND]D stretching band (Q-branch) of the CH3D molecule in the 2200 cm¿1 region was recorded. Most of the observed transitions have been assigned and some rotational-vibrational constants have been refined.© 1990 John Wiley & Sons, Ltd.

The Stokes Raman spectra of pure and hydrogenated amorphous germanium and silicon are discussed. First- and second-order structures due to the vibration of GeGe and SiSi bonds and also first-order structures due to GeH and SiH bonds are observed. The resonance behaviour and the polarization ratio of the observed structures are presented and interpreted in terms of a dielectric constant-bond polarizability model.

The absolute Raman intensities and depolarization ratios of CHC13 and CDC13 have been measured in the gas phase. These magnitudes, the Raman tensors (including signs), as well as the electro-optical parameters of the C-H and C-Cl bonds have been calculated within the frame of the bond-polarizability theory. Several approximations of the theory are reviewed. The influence of the vibrational force field upon the electro-optical parameters is also checked. © 1977 Taylor & Francis Group, LLC.

The infrared spectrum of hydrogenated a-Ge produced by sputtering in an ArH2 mixture is reported. Bond stretching, bending, and wagging bands are observed. From the integrated absorption of these bands the concentration of GeH and GeH2 bonds is determined. We also report annealing experiments at temperatures below and above that required for crystallization, the amount of this crystallization being determined by Raman scattering. The GeH2 bands disappear upon annealing faster than GeH and virtually none are left in the crystallized material which nevertheless still contains a significant proportion of GeH bonds. The possible structure of the GeH bonds in the crystalline phase is discussed.

The absolute Raman intensities of the fundamental bands of vapour HCCl3Jand DCCl3 have been measured with an experimental accuracy of ten per cent. The vibrational potential function for chloroform has been calculated by a standard least squares forceconstant refinement including data on anharmonicity corrected values of the 12C/13C displacements and also the absolute intensities measured in this work. The results are compared with those of Previous works and the influence of the intensity data upon the refinement is discussed.

3 pags., It is shown that the equilibrium and differential bond polarizabilities of CC bond determined experimentally from ethane and other saturated hydrocarbons can be transferred to diamond, provided local field corrections are taken into account. © 1982.

7 pags., 2 figs., 5 tabs., The cubic force field of methane has been investigated on the basis of the analysis of Raman scattering cross sections of binary overtones and combination bands. Seven absolute cross sections, ten symmetry cubic force constants, and the second derivative of the mean CH bond polarizability are the original results of present work. Some of these cubic force constants are determined with high accuracy. Most Ĥ22 rovibrational constants calculated by means of present anharmonic force field are in good agreement with the experimental values reported by various authors. © 1984 American Institute of Physics., We are indebted to J. Brandmiiller and H. W. Schrotter for moral support and to the Stiftung Volkswagenwerk of the Federal Republic of Germany for providing the high power laser source to obtain some of the results presented here.

The absolute Raman intensities and the depolarization ratios of the vibrational bands of gaseous CH4, CH3D, CH2D2, CHDS and CD4 have been computed here using a compact formulation of the bond polarizability theory, in its zero and first-order approximations. The agreement with experimental values taken from the literature is very good for the first-order approximation, although the difference between both approximations is not very large for these molecules. The derivatives of the polarizability with respect to the symmetry coordinates of methane are given with signs that are physically meaningful. © 1976 Taylor & Francis Group, LLC.

Publisher Summary This chapter discusses the recording of Stimulated Raman and infrared (IR) spectra using infrared difference frequency laser and stimulated-Raman-scattering spectrometers. The chapter presents an experiment in which a cw difference frequency IR laser spectrometer was used that was constructed following the design of Pine. The output of a frequency stabilized Ar+ laser and that of a commercial ring dye laser were mixed collinearly and focused into a 5 cm long, a-cut, lithium niobate crystal, held in a temperature-controlled oven to achieve phase matching. The generated IR radiation was recollimated to allow long absorption paths. Two indium antimonide detectors were used in a dual-beam configuration to obtain transmittance spectrum. Amplitude modulation and lock-in detection were then used. Data was acquired, stored, and processed with an AT-compatible computer. The whole experimental arrangement was schematically depicted. The setup allowed consecutive recording of Stimulated Raman and IR spectra just by the insertion of a couple of mirrors.

The cubic force field of methane has been investigated on the basis of the analysis of Raman scattering cross sections of binary overtones and combination bands. Seven absolute cross sections, ten symmetry cubic force constants, and the second derivative of the mean CH bond polarizability are the original results of present work. Some of these cubic force constants are determined with high accuracy. Most H22 rovibrational constants calculated by means of present anharmonic force field are in good agreement with the experimental values reported by various authors.