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The Raman spectra of ammonium sulfate solution are measured. Some insight into the experimentally observed line widths of the degenerate modes was obtained by carrying out an analysis of the unsymmetric structures of the partially solvated clusters.

Dual-broadband pure rotational coherent anti-Stokes Raman scattering is a valuable nonintrusive tool for gas diagnosis that provides simultaneous and time-resolved information about temperature and relative species concentration. A systematic investigation of single-shot precision and accuracy of simultaneous measurement of temperature and [O.sub.2]/[N.sub.2] concentration is presented. Various 02 concentrations(1.0-15.6%) in binary mixtures with [N.sub.2] have been investigated in a temperature range from 300 to 773 K and for pressures of 1-50 bars (0.1-5 MPa). A comparison of two least-sum-squared differences fit evaluation procedures for the spectral shape, weighted constantly or inversely with respect to the relative signal intensity, is given. The results yielded good accuracy and precision for measuring temperature as well as concentration. The influence of temperature, [O.sub.2] concentration, pressure, and evaluation techniques on both accuracy and precision is discussed. [C] 2000 Optical Society of America OCIS codes: 120.0120, 120.6780, 300.6230, 300.6420, 290.5860.

The near-infrared (NIR) laser Raman trapping system was applied to study liquid--liquid extraction in a single droplet in a subpicoliter range. The system trapped a single subpicoliter toluene droplet in water using the NIR laser beam and provided time-dependent optical images of the droplet during liquid--liquid extraction. The size of the trapped droplet gradually increased after p-nonylphenol solution was added in water. The Raman spectra of the droplet prove that the increase of the droplet size was caused by the absorption of p-nonylphenol from the water. The distribution coefficient of p-nonylphenol in the subpicoliter droplet was much higher than that in bulk solution.

We modify an algorithm for retrieving the absorption (a) and backscattering ([b.sub.b]) coefficient profiles in natural waters by inverting profiles of downwelling and upwelling irradiance so as to include the presence of Raman scattering. For a given wavelength of interest, [Lambda], the light field at the appropriate Raman excitation wavelength [[Lambda].sub.e] is first inverted to obtain the Raman source function at [Lambda]. Starting from estimates of the inherent optical properties at [Lambda], the contribution to the irradiances at [Lambda] from Raman scattering is then estimated and subtracted from the total irradiances to obtain the elastically scattered irradiances. We then inverted the elastically scattered irradiances to find new estimates of a and [b.sub.b] using our original method [Appl. Opt. 37, 3886 (1998)]. The algorithm then operates iteratively: The new estimates are used with the Raman source function to derive a new estimate of the Raman contribution, etc. Sample results are provided that demonstrate the working of the algorithm and show that the absorption and scattering coefficients can be retrieved with accuracies similar to those in the absence of Raman scattering down to depths at which the light field is significantly perturbed by it, e.g., with ~90% of the upwelling light field originating from Raman scattering. [C] 2000 Optical Society of America OCIS codes: 010.0010, 010.4450, 290.3200, 290.4210, 290.5860, 240.0290.

By means of radiative transfer simulations we developed a model for estimating the absorption a, the scattering b, and the backscattering [b.sub.b] coefficients in the upper ocean from irradiance reflectance just beneath the sea surface, R([O.sup.-]), and the average attenuation coefficient for downwelling irradiance, [.sub.1], between the surface and the first attenuation depth. The model accounts for Raman scattering by water, and it does not require any assumption about the spectral shapes of a, b, and [b.sub.b]. The best estimations are obtained for a and [b.sub.b] in the blue and green spectral regions, where errors of a few percent to [is less than] 10% are expected over a broad range of chlorophyll concentration in water. The model is useful for satellite ocean color applications because the model input, R([O.sup.-]) and [.sub.1], can be retrieved from remote sensing and the model output, a and [b.sub.b], is the major determinant of remote-sensing reflectance. [C] 2000 Optical Society of America OCIS codes: 010.4450, 030.5620, 280.0280, 290.5860.

An adaptive filter signal processing technique is developed to overcome the problem of Raman lidar water-vapor mixing ratio (the ratio of the water-vapor density to the dry-air density) with a highly variable statistical uncertainty that increases with decreasing photomultiplier-tube signal strength and masks the true desired water-vapor structure. The technique, applied to horizontal scans, assumes only statistical horizontal homogeneity. The result is a variable spatial resolution water-vapor signal with a constant variance out to a range limit set by a specified signal-to-noise ratio. The technique was applied to Raman water-vapor lidar data obtained at a coastal pier site together with in situ instruments located 320 m from the lidar. The micrometeorological humidity data were used to calibrate the ratio of the lidar gains of the [H.sub.2]O and the [N.sub.2] photomultiplier tubes and set the water-vapor mixing ratio variance for the adaptive filter. For the coastal experiment the effective limit of the lidar range was found to be approximately 200 m for a maximum noise-to-signal variance ratio of 0.1 with the implemented data-reduction procedure. The technique can be adapted to off-horizontal scans with a small reduction in the constraints and is also applicable to other remote-sensing devices that exhibit the same inherent range-dependent signal-to-noise ratio problem. [C] 2000 Optical Society of America OCIS codes: 070.0070, 070.6110, 280.0280, 280.3640.

We measured the ortho-para conversion rate in solid hydrogen by using Raman scattering in a diamond-anvil cell, extending previous measurements by a factor of 60 in pressure. We confirm previous experiments that suggested a decrease in the conversion rate above about 0.5 GPa. We observe a distinct minimum at 3 GPa followed by a drastic increase in the conversion rate to our maximum pressure of 58 GPa. This pressure enhancement of conversion is not predicted by previous theoretical treatments and must be due to a new conversion pathway. high-pressure physics | Raman spectroscopy | solid hydrogen

Barium ferrite films with high coercivity, large magnetic anisotropy, good crystal orientation and crystallinity with hexagonal symmetry have been prepared on single crystal sapphire substrates by laser in-situ deposition. The structures of these films were characterized by x-ray diffractometry. X-ray diffraction pattern shows a preferential c-axis orientation normal to the film plane at a deposition temperature of 900 [degrees] C. The magnetic properties of the films were analysed by a Vibrating Sample Magnetometer and surface morphology was measured by an Atomic Force Microscope. The thin film composition was studied by Raman spectra in qualitative manner.

Residual mechanical stresses are measured for ultra thin films, Cr, Co-alloy and carbon and their combinations by means of an optical interferometer. The individual stress is additive. The dependence of the carbon, Cr, and Co-alloy film stresses on film thickness indicates that the residual stress originates from film deposition processes as an interfacial phenomenon. The dependence of stress on the chemical properties of the carbon film is also studied in this paper. Index Terms--carbon, Co-alloy, Cr, Raman spectra for diamond like carbon, residual stress, thin film

In a very low pressure gas, the Raman shift is not only spatially coherent, but parametric too. Spatial coherence means that the wave surfaces are preserved; parametric means that the [...]

Coherent anti-Stokes Raman-scattering (CARS) used as a probe mechanism in a time resolved pump-probe scheme is demonstrated as a powerful tool in optical time-resolved spectroscopy for determining the population flow in specific normal modes of a molecular system. Results provide the greater insight into the mechanism of non-Born-Oppenheimer dynamics.

Indium tin oxide as the electrode substrate is utilized, enabling surface plasmon absorption as well as electrochemical and surface-Enhanced Raman Scattering (SERS) characterization of the nanoparticle films to be undertaken. The results demonstrate a straightforward preparation of nanoparticle films exhibiting well-defined electrochemical and adsorbate vibrational properties.

A shift in vibrational frequency in response to an externally applied electric field is observed in the surface-enhanced Raman scattering spectra of self-assembled monolayers (SAMs) functionalized with pendant nitrile effect. A method for the observation of E field within the diffuse double-layer at SAM-modified tuning rates of a small, isolated vibrational probe molecule is presented.

Picosecond resolution shadowgraphy is a powerful tool for measurement of high-intensity laser propagation instabilities through underdense plasma. It is shown that as the plasma density increases, the laser beam is subject to severe filamentation instabilities--likely due to the effect of stimulated Raman side-scattering. At higher plasma densities, scattering and absorption are so severe that the propagation distance of the high intensity laser pulse is reduced. Index Terms--Intense laser plasma.

Remarkable reversals of vibrational frequency shifts in radical cations of Ni(II) porphines with n-propyl or tert-butyl substituents on the meso-carbon atoms are described. These reversals offer proof that out-of-plane distortions of the porphyrin mix the two highest occupied molecular orbitals (HOMO). The HOMO is destabilized by these distortions, as gleaned from the decline of the porphyrin oxidation potential and of the energies of the pi-pi* electronic transitions.

Band III excitation resonance Raman (RR) spectra of deoxymyoglobin is qualitatively different from that of either B or Q-state excitation. The presence of different intense low-frequency modes suggests that there exists a strong coupling between these modes and resonant charge-transfer transition. An analysis of the intensity of the band III excitation RR features helps examine the strength of the vibronic coupling and the excited state dynamics.

Picosecond pump-probe methods help analyze Raman scattering from excited electronic states of Zn(II)octaethylporphyrin. The S1 state reveals weak Jahn-Teller distortion whereas the T1 state reveals strong Jahn-Teller distortion. Observation of different Jahn-Teller distortions implies that excited states of metalloporphyrins exhibit different spin multiplicities.

Detailed information about the changes in nuclear equilibrium geometry may be gained through a combined quantitative analysis of resonance Raman scattering cross section and charge-transfer absorption. Although other conventional time-domain pump-probe techniques exist, the proposed approach generates more accurate results. Such an approach has also been proven efficient in calculating molecular and solvent reorganization parameters.

A study was conducted to examine conjugates between cytochrome c and colloidal silver particles that support technique of positioning a biomolecule analyte between two metal surfaces. Silver sols were obtained through the aqueous reduction of AgNO3 with trisodium citrate. Results indicated that Cc:au conjugate adsorbed to aggregates of colloidal silver supported greater stability to conformational and spin-state changes than Cc directly adsorbed to silver aggregates.

A study was conducted to analyze the weak, polarized Raman band assigned to the v1 CdO6 mode of the hexaquo Cd(II) ion over the temperature range 25-152 degrees C. The true vibrational contribution of the band was determined using the isotropic scattering geometry. The Raman spectra of the Cd(ClO4)2 solution was then obtained at three different temperatures. In addition, ab initio geometry optimizations were performed at the Hartree-Fock and second-order Moller-Plesset levels of theory.