Rotational Raman Spectroscopy Research Articles

Effective Suppression of Stray Light in Rotational Coherent Anti-Stokes Raman Spectroscopy Using an Angle-Tuned Short-Wave-Pass Filter

Stray light interference is a common problem in spontaneous rotational Raman spectroscopy and rotational coherent anti-Stokes Raman spectropscopy (CARS). The reason is that the detected spectrum appears in the spectral vicinity of the probe beam wavelength, and stray light at this wavelength from optics and surfaces is hard to suppress. In this Note, efficient suppression of stray light is demonstrated for rotational CARS measurements using a commercially available short-wave-pass filter. By angle-tuning this filter with a specified cut-off wavelength at 561 nm, the cut-off wavelength could be tuned to a desired spectral position so that more than 80% transmission is achieved as close as 15 cm(-1) (approximately 0.4 nm) from the probe beam wavelength of 532.0 nm, while the intensity at this wavelength is suppressed by two orders of magnitude.

Laser Thomson Scattering, Raman Scattering and laser-absorption diagnostics of high pressure microdischarges

Laser scattering experiments were performed in high pressure (100s of Torr) parallel-plate, slot-type DC microdischarges operating in argon or nitrogen. Laser Thomson Scattering (LTS) and Rotational Raman Scattering were employed in a novel, backscattering, confocal configuration. LTS allows direct and simultaneous measurement of both electron density (ne) and electron temperature (Te). For 50 mA current and over the pressure range of 300 − 700 Torr, LTS yielded Te = 0.9 ± 0.3 eV and ne = (6 ± 3)·1013 cm−3, in reasonable agreement with the predictions of a mathematical model. Rotational Raman spectroscopy (RRS) was employed for absolute calibration of the LTS signal. RRS was also applied to measure the 3D gas temperature (Tg) in nitrogen DC microdischarges. In addition, diode laser absorption spectroscopy was employed to measure the density of argon metastables (1s5 in Paschen notations) in argon microdischarges. The gas temperature, extracted from the width of the absorption profile, was compared with Tg values obtained by optical emission spectroscopy.

Coupled Translation−Rotation Eigenstates of H2, HD, and D2 in the Large Cage of Structure II Clathrate Hydrate: Comparison with the Small Cage and Rotational Raman Spectroscopy

We report fully coupled quantum five-dimensional calculations of the translation-rotation (T-R) energy levels of one H(2), HD, and D(2) molecule confined inside the large hexakaidecahedral (5(12)6(4)) cage of the structure II clathrate hydrate. Highly converged T-R eigenstates have been obtained for excitation energies beyond the j = 2 rotational levels of the guest molecules, in order to allow comparison with the recent Raman spectroscopic measurements. The translationally excited T-R states are assigned with the quantum numbers n and l of the 3D isotropic harmonic oscillator. However, the translational excitations are not harmonic, since the level energies depend not only on n but also on l. For l > 1, the T-R levels having the same n,l values are split into groups of almost degenerate levels. The splitting patterns follow the predictions of group theory for the environment of T(d) symmetry, which is created by the configuration of the oxygen atoms of the large cage. The 2j + 1 degeneracy of the j = 1 and 2 rotational levels of the encapsulated hydrogen molecule is lifted entirely by the angular anisotropy of the H(2)-cage interaction potential. The patterns and magnitudes of the j = 1, 2 rotational level splittings, and the energies of the sublevels, in the large cage are virtually identical with those calculated for the small cage. This is in agreement with, and sheds light on, the observation that the S(0)(0) (j = 0-->2) bands in the rotational Raman spectra measured for simple H(2) hydrate and the binary hydrate of H(2) with tetrahydrofuran are remarkably similar with respect to their frequencies, widths, shapes, and internal structure, when the H(2) occupancy of the large cage of simple H(2) hydrate is low.

Three-dimensional gas temperature measurements in atmospheric pressure microdischarges using Raman scattering

Spatially resolved three-dimensional rotational Raman spectroscopy of ground state nitrogen was used to measure the gas temperature (Tg) in a normal dc glow microdischarge (300μm gap between 0.5×0.05mm2 parallel electrodes) in pure N2. An original backscattering confocal optical system with a spatial resolution of ∼40μm was developed for collecting Raman spectra. Gas temperatures were measured at several points across the gap as well as along the axis perpendicular to the discharge plane. Tg peaked near the cathode and was 1200K in the negative glow of a 500Torr, 20mA discharge.

Rotational Raman spectroscopy of ethylene using a femtosecond time-resolved pump-probe technique

Femtosecond Raman-induced polarization spectroscopy (RIPS) was conducted at low pressure (250 mb at 295 K and 400 mb at 373 K) in ethylene. The temporal signal, resulting from the beating between pure rotational coherences, was measured with a heterodyne detection. The temporal traces were converted to the frequency domain using a Fourier transformation and then analyzed thanks to the D2hTDS software (http://www.u-bourgogne.fr/LPUB/shTDS.html) dedicated to X2Y4 molecules with D2h symmetry. The effective Hamiltonian was expanded up to order 2, allowing the determination of five parameters with an rms of 0.017 cm(-1). Special care was taken in the precise modeling of intensities, taking into account all instrumental effects. Relative intensities were fitted (with an rms of 7.2%) and two polarizability operators were determined.

An apparatus to control and monitor the para-D 2 concentration in a solid deuterium, superthermal source of ultra-cold neutrons

Controlling and measuring the concentration of para-D 2 is an essential step toward realizing solid deuterium as an intense ultra-cold neutron source. To this end, we implemented an experimental technique to convert para- to ortho-deuterium molecules by flowing D 2 gas through a cryogenic cell filled with paramagnetic hydrous ferric oxide granules. This process efficiently reduced the para-D 2 concentration from 33.3% to 1.5%. Rotational Raman spectroscopy was applied to measure the residual para-D 2 contamination to better than 2 parts in 10 3, and the hydrogen contamination to 1 part in 10 3. We also contrast our optical technique to conventional thermal conductivity measurements of the para-D 2 concentration, reporting some of the relevant strengths and weaknesses of our implementation of each technique.

Rotation–vibration interaction in 4He trimers

An approximate treatment of the rotation–vibration interaction is considered in the helium trimer system to study the existence of bound states with non-zero ( J=1) total angular momentum and to elucidate its Efimov character. With the interaction used here, at least one bound state is found. In terms of a λ-parameter modifying the strength of the two-body potential, the radial part of the wave function changes dramatically with tiny variations around the physical value λ=1. High-resolution rotational Raman spectroscopy in a supersonic beam expansion is proposed as a feasible way of observing the bound state predicted.

Measurement of the Raman polarizability anisotropy for the v = 1 pure rotational Raman transition in H 2 by rotational Raman spectroscopy

A combination of stimulated Raman pumping and rotational Raman spectroscopy is used to accomplish the first measurement of the polarizability anisotropy γ11,13 (355 nm) for the S11 (1) transition in molecular hydrogen H2. Saturation of the Q01(1) transition connecting the |X1 Σ+ g, v = 0, J = 1 > state to the |X1 Σ+ g, v = 1, J = 1 > state in H2 by stimulated Raman pumping is the critical element in this experiment. The observed intensities of the rotational Raman lines for these states allow an estimate of γ11,13 (355 nm) as 0.358 ± 0.004 Å3. A comparison of this value to that obtained from fundamental ab initio calculations in H2 also is possible for the first time.

Measurement of the Raman polarizability anisotropy for the v=1 pure rotational Raman transition in H 2 by rotational Raman spectroscopy

Measurement of the Raman polarizability anisotropy for the v=1 pure rotational Raman transition in H 2 by rotational Raman spectroscopy

Subpicosecond predissociation dynamics of the methyl radical Rydberg 3 s state

The subpicosecond dissociation dynamics of the methyl radical 3 s Rydberg state have been examined using rotational resonance Raman spectroscopy. The rovibronic dependence of the excited state predissociation rates and lifetimes are obtained for the B̃ state origin vibrational level of CH3 and CD3. Analysis of the tunneling rates using a cubic potential barrier yields estimates for the height (2200 cm−1) and position of the barrier along the dissociation coordinate (1.38 Å). A comparison of the potential energy surface parameters for the Rydberg 3 s states of methyl radical and ammonia is presented.

ChemInform Abstract: Structure of Dicyanoacetylene by Electron Diffraction and Coherent Rotational Raman Spectroscopy.

ChemInformVolume 20, Issue 44 Physical Organic Chemistry ChemInform Abstract: Structure of Dicyanoacetylene by Electron Diffraction and Coherent Rotational Raman Spectroscopy. K. W. BROWN, K. W. BROWN Dep. Chem., Oreg. State Univ., Corvallis, OR 97331, USASearch for more papers by this authorJ. W. NIBLER, J. W. NIBLER Dep. Chem., Oreg. State Univ., Corvallis, OR 97331, USASearch for more papers by this authorK. HEDBERG, K. HEDBERG Dep. Chem., Oreg. State Univ., Corvallis, OR 97331, USASearch for more papers by this authorL. HEDBERG, L. HEDBERG Dep. Chem., Oreg. State Univ., Corvallis, OR 97331, USASearch for more papers by this author K. W. BROWN, K. W. BROWN Dep. Chem., Oreg. State Univ., Corvallis, OR 97331, USASearch for more papers by this authorJ. W. NIBLER, J. W. NIBLER Dep. Chem., Oreg. State Univ., Corvallis, OR 97331, USASearch for more papers by this authorK. HEDBERG, K. HEDBERG Dep. Chem., Oreg. State Univ., Corvallis, OR 97331, USASearch for more papers by this authorL. HEDBERG, L. HEDBERG Dep. Chem., Oreg. State Univ., Corvallis, OR 97331, USASearch for more papers by this author First published: October 31, 1989 https://doi.org/10.1002/chin.198944043AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume20, Issue44October 31, 1989 RelatedInformation

Structure of dicyanoacetylene by electron diffraction and coherent rotational Raman spectroscopy

Structure of dicyanoacetylene by electron diffraction and coherent rotational Raman spectroscopy

Concerning the Quantitative Analysis of Hydrogen Gas by Rotational Raman Spectroscopy

There has been considerable recent interest in using rotational Raman spectroscopy to analyze gaseous mixtures of hydrogen diatomic isotopes. Indeed, all six isotopic diatomic species of hydrogen, deuterium, and tritium may be identified by Raman analysis within a 1000 cm−1 region adjacent to the exciting laser line. During the course of developing an analytical capacity to measure these isotopes using a slightly modified commercial instrument, it became important to carefully evaluate the influence of the temperature of the gas sample on the rotational Raman intensity variability. This note enunciates the salient features of our results for H2 gas. Additional details may be found in forthcoming documents.

Variation of the polarizability with the nuclear configuration as studied by rayleigh scattering and rotational raman spectroscopy in H 2S and D 2S

Experimental evidence of a difference of optical anisotropy between H 2S and D 2S and a variation of the R ba ratio in the rotational Raman spectra of both molecules have been previously reported. A quantitative and consistent interpretation of these results is tentatively given on the ground of variations of the nuclear configuration due to the isotopic effect and/or the centrifugal distortion.

Rotational Raman scattering from premixed and diffusion flames

Use of rotational Raman spectroscopy as a flame probe is examined. Results of rotational and vibrational Raman scattering from hydrogen oxygen, methane-air and propane-air flames are presented. Time-averaged temperatures are measured, both below and above the inner cones of the premixed flames, based upon rotational Raman scattering from the major species (N 2, O 2, H 2 and CO 2). Corrections for vibrational-rotational interactions and for the effects of rotational transitions from vibratinally excited molecules are included in the temperature calculations. For hydrogen or methane flames, temperatures based upon rotational Raman scattering from N 2 or O 2 have lower uncertainties (1–4%) than those based upon vibrational Raman scattering (3–9%) because rotational Raman transitions are generally more intense and give rise to many more transitions. Scattering from CO 2, H 2O, or C 3H 8 does not seriously interfere with rotational Raman temperature measurements in the flames studied. It is concluded that rotational Raman spectroscopy can be a useful nonperturbing probe of concentrations and temperatures in atmospheric pressure flames. Rotational Raman intensity factors relative to N 2, are obtained from room temperature pure rotational Raman spectra to be 2.61 ± 0.13 for O 2 and 0.20 ± 0.05 for HCl.

A method for background light rejection in multiplexed rotational Raman spectroscopy with Fabry–Perot interferometers

AbstractThe feasibility of using Fabry–Perot interferometers in the remote sensing of gaseous pollutants via their rotational Raman spectra depends upon the development of a method of rejecting back‐scattered light arising from Mie scattering from dust, Rayleigh, and Raman scattering from the abundant gases in the region being observed. We present measurements of the rejection of Rayleigh and rotational Raman light using Fabry–Perot interferometers in reflection to demonstrate a method of reducing background interference by more than two orders‐of‐magnitude.

Pure rotational Raman spectroscopy of diatomic molecules

Outlines the experimental procedures and theory necessary to observe and interpret rotational Raman spectra of diatomic molecules.