High Resolution Stimulated Raman Spectra Research Articles

Collisional line widths of autoperturbed N 2: Measurements and quantum calculations

In this work we present new experimental and theoretical values for the line broadening coefficients of the Q-branch Raman lines of autoperturbed N 2. For the experimental determination of the coefficients, high resolution stimulated Raman spectra of the Q-branch of N 2 at different pressures were obtained at 77, 194 and 298 K. Simultaneously, quantum dynamical calculations, performed on two potential energy surfaces, were carried out for the system between 77 and 298 K, rendering a set of theoretical line broadening coefficients that could be directly compared to those obtained from the present measurements and the previous ones. Within the limit of considering the colliding molecules distinguishable we discuss the ortho and para contributions to the pressure broadening cross-sections. Because such calculations are time consuming we indicate routes to circumvent this difficulty. We observe a reasonable agreement between theoretical and experimental values of the collisional line broadening coefficients at all the studied temperatures.

The ν5 band of 12CH 313CH 3: High resolution stimulated Raman spectrum and global three band analysis

Rotationally resolved spectrum of 12CH 3 13CH 3 in the region of ν 5 vibrational fundamental (C C stretch) was observed using stimulated Raman spectroscopy. This spectrum was analyzed with data from the ν 12 fundamental and transitions from the ν 6, 2 ν 6– ν 6, and 3 ν 6 torsional bands using a 3-state fit. One torsional component of the ν 5 fundamental is perturbed, interacting with its partner in the ν 6 = 4 of the torsional stack of the ground vibrational state. As for normal ethane, the coupling was successfully modeled using a Fermi-type interaction. The results mirror that of 12CH 3 12CH 3 in that the inclusion of the Fermi-type interaction reduces the required number of terms in the Fourier expansion of the torsional potential for the ground vibrational state from three (in the 2-state fit) to one, only the term in the barrier height is required.

The ν3 band of CD 3CD 3: High resolution stimulated Raman spectrum and global three band analysis

Stimulated Raman spectroscopy has been used to study rotationally resolved Q-branch of the ν 3 band. This spectrum is analyzed with data from the ν 9 fundamental, ν 9 + ν 4 − ν 4 hot band and transitions from ν 4 and 3 ν 4 torsional bands. One torsional component of the ν 3 fundamental is near degenerate with its interacting partner v 4 = 5 of the ground state torsional bath. The coupling was modeled using a Fermi-type interaction. The introduction of the Fermi-type interaction causes a large change in the barrier height for the ground vibrational state and makes the barrier shape parameter redundant, indicating the vibrational contributions to the experimental barrier shape are dominant.

Theoretical and experimental analysis of N2–H2 stimulated Raman spectra

The paper reports on a detailed study of the N2–H2 collisional line broadening coefficient. High resolution stimulated Raman spectra of nitrogen–hydrogen mixtures have been recorded at liquid nitrogen and room temperatures. Corresponding linewidth calculations have been performed at temperatures between 77 and 500 K using the semiclassical Robert and Bonamy model for J rotational quantum numbers varying between 0 and 11. Comparison between experimental data and calculated results shows good agreement at room temperature using an adjusted value for the kinetic diameter.

Study of the Fundamental Bands of 70GeD 4 by High-Resolution Raman and Infrared Spectroscopy: First Experimental Determination of the Equilibrium Bond Length of Germane

The four fundamental bands of 70GeD 4 have been analyzed using the STDS software developed in Dijon (http://www.u-bourgogne.fr/LPUB/sTDS.html). Both infrared and Raman spectra were used to observe all fundamental bands. Infrared spectra of monoisotopic 70GeD 4 were recorded in the regions 600 and 1500 cm −1 using the Bruker 120HR interferometer at Wuppertal. The resolution (1/maximum optical path difference) was between 2.3 and 3.3×10 −3 cm −1 for the ν 3 and ν 4 infrared-active fundamental bands as well as for the interacting ν 2 band. A high-resolution stimulated Raman spectrum of the ν 1 band has been recorded in Madrid. The instrumental resolution of the Raman spectrum was 3.3×10 −3 cm −1. We have performed a global fit of the ground state, ν 2/ν 4 bending dyad, and ν 1/ν 3 stretching dyad. We have used 1146, 139, and 676 assigned lines for ν 2/ν 4, ν 1, and ν 3, respectively. The standard deviation is 2.2×10 −3 cm −1 for the bending dyad, 1.6×10 −3 cm −1 for the ν 3 infrared lines, and 1.7×10 −3 cm −1 for the ν 1 Raman lines. These results enabled us to perform the first experimental determination of the equilibrium bond length of germane as r e =1.5173(1) Å.

High-Resolution Stimulated Raman Spectrum of F2

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.

Study of collisional effects on band shapes of the ν1/2ν2 Fermi dyad in CO2 gas with stimulated Raman spectroscopy. III. Modeling of collisional narrowing and study of vibrational shifting and broadening at high temperature

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 γv and line shifting δv. 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, 2176 (1990); B. Lavorel et al., J. Chem. Phys. 93, 2185 (1990)] entirely determine the temperature dependence in the 295–900 K range of Raman band shapes of ν1 and 2ν2 in a large pressure range. These results will be very useful in CARS thermometry. A few coherent anti-Stokes Raman spectra (CARS) recorded in the 1100–1300 K domain are consistent with extrapolations of the 295–900 K data.

Vibrational–torsional coupling. High-resolution stimulated Raman spectrum of the ν3 band of ethane (12C2H6)

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.

Wavelengths measurements of continuous wave lasers with a wavemeter. Applications to high resolution Raman spectra calibration

Describes the mechanical, optical and electronic improvements of the wavemeters which has been presented previously (J. Optics, vol.15 , no.1, p.31-41, 1984). These improvements have made the apparatus (Michelson interferometer) more reliable. Measurement accuracy has been improved. The wavemeter has been tested with two reference lasers (Ar+ at 514 nm and He-Ne at 633 nm), stabilized on hyperfine components of 127I2 The measurement uncertainties have been evaluated (systematic and statistical dispersion). The experimental results exhibit an accuracy of the interferometer equal to 3,5 10-9. They describe two examples of high resolution stimulated Raman spectra calibration.

High-resolution cw stimulated Raman spectroscopy in molecular hydrogen

We report the application of low-power cw laser sources in obtaining high-resolution stimulated Raman spectra (SRS) of the Q01 (1) transition in molecular hydrogen. Fully resolved spectra of both the real and the imaginary parts of the Raman susceptibility, obtained with a resolution of <25 MHz, show a motionally narrowed minimum linewidth of 250 ± 5 MHz. The cw SRS techniques reported herein should find a variety of applications in high-resolution Raman studies.