Search results for "Q-BRANCH"
showing 10 items of 16 documents
Nonlinear Raman Spectroscopy in Gases
1992
0022-2860; Recent progress in high-resolution non-linear coherent Raman spectroscopy in the gas phase is reviewed. An instrumental spectral resolution of less than 100 MHz can be routinely achieved. It is limited by the convoluted linewidths of the lasers used for excitation and is of particular advantage in the gas phase, where the rotational structure of vibrational bands is to be resolved. It also allows the measurement of linewidths and line positions with an accuracy of 60 MHz when an appropriate wavemeter is used for calibration. After a short overview of the various techniques being used, examples of recent results of the evaluation of measurements on nitrogen, oxygen, carbon dioxide…
A direct study of the vibrational bending effect in line mixing: The hot degenerate 11(1)0<-01(1)0 transition of CO2
1997
0022-4073; The study of the isotropic Raman Q-branch of a hot band Pi <-- Pi allows one to establish a direct connection between the vibration-rotation angular momentum coupling and the resulting spectra. Due to the l-doubling, the Q-branch is split into two subbranches characterized by either even or odd rotational quantum number j. The vibrational bending reduces the rotational transfer rates inside each of these subbranches by a factor of about two and induces an inter-subbranch coupling. The expected propensity rule towards conservation of the parity index for high rotational levels is well observed. Calculated spectra are in excellent agreement with CARS experiments for the nu(1) + nu(…
Stimulated Raman and Cars Spectroscopy of ν1 and 2ν2 (A1) Bands of 12CF4
1994
Two experimental coherent Raman techniques, stimulated Raman and coherent anti-Stokes Raman spectroscopy (CARS), were employed to study the Raman spectrum of CF 4 in the 900 cm −1 region. The stimulated Raman and CARS spectra of the ν 1 band of CF 4 were recorded at high resolution. The analysis of these spectra enabled some spectroscopic constants of this band to be refined and higher order constants to be determined for the first time. The first high-resolution CARS spectrum of the 2ν 2 (A 1 ) harmonic band is also presented. The rotational transitions of this band up to J = 40 were assigned and the first set of spectroscopic constants for this sub-level were determined. These results imp…
Collisional Raman Linewidths of Nitrogen at High-Temperature (1700-2400 K)
1995
0146-9592; New high-temperature measurements of collisional linewidths of the Roman Q branch of nitrogen have been performed at 1700-2400 K with stimulated Raman spectroscopy in a tungsten filament. We fitted these data together with previous data obtained in the 295-1500-K range to redetermine the parameters of the relaxation models used in coherent anti-Stokes Raman spectroscopy thermometry. The improvement in the accuracy of the temperature measurement has been checked. Semiclassical calculations of linewidths in the 1700-2400-K range agree with the experimental data and have been extended to even higher temperatures.
Electrostrictive limit in the detection of weak stimulated Raman signals in gases
1997
0377-0486; It is shown experimentally that, in stimulated Raman spectroscopy, electrostriction induced by the pump laser gives rise to a non-resonant signal detected on the probe laser. This phenomenon limits the detectivity of the experiment. A qualitative interpretation is given. (C) 1997 by John Wiley & Sons, Ltd.
Determination of concentrations in ternary and quaternary molecular gas mixtures using femtosecond Raman spectroscopy
2002
European Conference on Nonlinear Optical Spectroscopy MAR 18-19, 2002 VILLIGEN, SWITZERLAND; Measurements of concentrations in gas mixtures of three and four molecular components are presented. They rely on a femtosecond time-resolved pump-probe technique based on Raman-induced polarization spectroscopy. The rotational time response of the molecular gas mixture is measured as a function of the pump-probe time delay. No selective frequency tunability is needed as the molecular rotational spectra are excited within the laser bandwidth. The results obtained from experiments performed at room temperature in N2O-CO2-N2 and N2O-CO2-O2-N2 mixtures are presented and the accuracy of the method is di…
Study of Collisional Effects on Band Shapes of the ν1/2ν2 Fermi Dyad in CO2 Gas with Stimulated Raman-Spectroscopy .3. Modeling of Collisional Narrow…
1994
0021-9606; High resolution stimulated Raman spectra (SRS) of the ν1/2ν2 Fermi dyad of CO2 have been recorded in the 0.4-22. amagat density range at 700 K and in the 0.6-16 amagat density range at 900 K. The data have been successfully analyzed with a theoretical model taking into account both rotational line mixing through the energy corrected sudden-polynomial (ECS-P) law for the relaxation matrix and vibrational line broadening gamma(v) and line shifting delta(v). The two vibrational parameters have been accurately determined from fit to the experimental spectra. These new high temperature data together with previous data obtained at 295 and 500 K [B. Lavorel et al., J. Chem. Phys. 93, 21…
Dual-broadband rotational CARS modelling of nitrogen at pressures up to 9 MPa. II. Rotational Raman line widths
2002
International audience; Rotational coherent anti-Stokes Raman spectroscopy (CARS) is a well-established spectroscopic technique for thermometry at pre-combustion temperatures an atmospheric pressure. However, at pressures of several MPa, a previous investigation revealed large discrepancies between experimental data and the theoretical model. A re-evaluation has been made of these data (at room temperature and in the range 1.5-9 MPa) with two improvements to the spectral code. The first is the inclusion of an inter-branch interference effect, which is described in detail in Paper I. The second is the use of experimental S-1-branch Raman line widths measured at 295 K, with a temperature depe…
Accurate Spectroscopic Constants of Nitrogen Determined from Stimulated Raman Spectra of the Fundamental and 1st Hot Bands
1990
0377-0486; Nitrogen specta of the Q-branch of the fundamental and the first hot bands were recorded with a high-resolution stimulated Raman spectrometer at atmospheric pressure and ca. 1300 K. The absolute frequencies of the Raman lines were measured with high accuracy, leading to a refinement of spectroscopic constants. A temperature estimation was also performed from the Raman intensities.
Collisional shifting and broadening coefficients for the rovibrational anisotropic lines of the v1/2v2 Fermi dyad in CO2 gas studied by stimulated Ra…
1998
0377-0486; High-resolution stimulated Raman spectroscopy was applied to the study of collisional broadening and shifting for rovibrational anisotropic Raman Lines of the Fermi dyad of molecular carbon dioxide, The O(J) lines of the v1 band and the S(J) lines of the 2v2 band were recorded at 295 K. The pressure-induced line shifts were obtained and compared with the overall shift of the high-density Raman Q-branch, A rotational quantum number dependence of the rovibrational line broadening coefficients was observed. The experimental line broadening coefficients were used in order to check the ability of two theoretical methods (random phase approximation and sum rule) for calculating the lin…