G. J. Rosasco

Dynamics of molecular reorientational motion and vibrational relaxation in liquids. Chloroform

Vibrational and rotational (dipole and second−order tensor) correlation functions were obtained by Fourier inversion of infrared and Raman vibrational band contours of the three ∥ and one ⊥ fundamental of liquid CHCl3, CDCl3, and isotopically pure CH35Cl3. All correlation functions are nonexponential at short times and approximately exponential for long times. The symmetry axis of the molecule reorients by ’’free’’ jumps of about 1/3 rad, turning through a root−mean−square angle of 1 radian within 2psec by about 13 orientational jumps. Computer simulations show that J diffusion is too fast beyond 1 psec and that M diffusion fits the data up to 4 psec (τJ = 0.12 psec); thereafter, M diffusion is too slow. The Raman rotational correlation time is approximately equal to the NMR quadrupolar correlation time; the infrared rotational correlation time is only 0.75 of a corresponding dielectric relaxation time. Vibrational relaxation in the symmetric near−infrared carbon−hydrogen stretch is of the same order of i...

Line interference effects in the vibrational Q-branch spectra of N2 and CO

Self-broadened (≈20–200 kPa) Q-branch spectra are measured by high-resoIution cw-stimulated Raman spectroscopy. Line overlap in these spectra is described using a relaxation matrix formalism and a first-order (in density) solution to the resulting equation is used to fit the data. The parameters of this model are analyzed in terms of rates of rotational energy transfer.

Application of a new Raman microprobe spectrometer to nondestructive analysis of sulfate and other ions in individual phases in fluid inclusions in minerals

Rosascoet al. (1975), reported the first successful application of laser-excited Raman spectroscopy for the identification and nondestructive partial analysis of individual solid, liquid, and gaseous phases in selected fluid inclusions. We report here the results of the application of a new instrument, based on back-scattering, that eliminates many of the previous stringent sample limitations and hence greatly expands the range of applicability of Raman spectroscopy to fluid inclusions. Fluid inclusions in many porphyry copper deposits contain 5–10 μm ‘daughter’ crystals thought to be anhydrite but too small for identification by the previous Raman technique. Using the new instrument, we have verified that such daughter crystals in quartz from Bingham, Utah, are anhydrite. They may form by leakage of hydrogen causing internal autooxidation of sulfide ion. Daughter crystals were also examined in apatite (Durango, Mexico) and emerald (Muzo, Colombia). Valid analyses of sulfur species in solution in small fluid inclusions from ore deposits would be valuable, but are generally impossible by conventional methods. We present a calibration procedure for analyses for SO42− in such inclusions from Bingham, Utah (12,000 ± 4000 ppm) and Creede, Colo. (probably < 500 ppm). A fetid Brazilian quartz, originally thought to contain liquid H2S, is shown to contain only HS− in major amounts.

Internal field resonance structure: Implications for optical absorption and scattering by microscopic particles

Mie scattering theory is used to calculate the efficiency factors for absorption by microscopic dielectric spheres. Resonances in the efficiency factors for absorption and resonances in the amplitudes of the electric and magnetic multipoles which occur in an expansion of the fields inside the dielectric sphere are discussed. Several trends in the strengths and width of the various resonances as functions of the absorption coefficient of the sphere, size parameter, multipole order, and multipole resonance number are given. A formal solution for elastic (Mie) and inelastic (Raman) scattering by microscopic particles is derived from the extinction theorem. With this background, some implications of the resonances in the interpretation of absorption, fluorescence, and Raman scattering by microscopic particles are discussed.

Laser-Excited Raman Spectroscopy for Nondestructive Partial Analysis of Individual Phases in Fluid Inclusions in Minerals

Laser-excited Raman spectroscopy has been successfully applied to the identification and partial analysis ofsolid, liquid, and gaseous phases in fluid inclusions. The procedure is no panaceaforproblems ofanalysis offluid inclusions, but some uniquefeatures make it very useful. In particular, the measurement is performed in situ; it is nondestructive; and it can produce qualitative and quantitative data, some of which cannot be obtained otherwise, for samples as small as 10-9 gram. The analysis of fluid inclusions in minerals provides important data related to many mineralogical, geological, and geochemical processes. Inclusions represent samples of the fluids from which the host minerals have crystallized (1) or with which they have reacted (2). They may be trapped either during the growth of the host mineral or at one or more later times. Most samples thus contain more than one generation of inclusions, sometimes of greatly different ages and fluid compositions. During cooling, aftcr the fluid has been trapped, two or more phases gener-

Raman Microprobe Spectra and Vibrational Mode Assignments of Talc

The Raman spectra of talc microparticles have been obtained with the Raman microprobe over the frequency range 100 to 3800 cm−1. The vibrational modes are discussed in terms of an idealized unit cell (1-M polymorph) of C2h symmetry. An electrostatic dipole-dipole interaction is used to compare the Raman and infrared active branches. Assignments of the Raman active stretching modes of the silicate sheet are found to support previous infrared assignments. Estimates of intrasheet dipole-dipole interactions are obtained.

Raman Microprobe Characterization of Residual Carbonaceous Material Associated with Urban Airborne Particulates

Analyses of individual urban airborne particulates were conducted in the Raman microprobe. In addition to the spectral features characteristic of the particle, two features at ∼1350 and ∼1600 cm−1 have been observed. The appearance of these bands is found to vary a function of the laser irradiance. By modeling experiments, it is demonstrated that these two bands can be explained by the presence of carbon in a form analogous to polycrystalline graphite. In air particulates the source of the carbon can be either “graphitic soot” or an organic “contaminant” which converts to polycrystalline graphite upon exposure to the laser beam.

Measurement and prediction of Raman Q-branch line self-broadening coefficients for CO from 400 to 1500 K

The J and temperature dependence of the self‐broadening coefficients for the Raman Q‐branch lines of pure CO have been experimentally determined for Q(J) transitions with J=0–38 and for temperatures in the range 400–1500 K. It is shown that a fitting law, based on a modified exponential energy‐gap model for the rates of state‐to‐state rotationally inelastic collisions, can account for the observed J dependence. The two parameters that determine the J dependence are found to be essentially independent of temperature. A temperature scaling function, recently proposed for N2, is added to the basic rate law, and accurate predictions of both the J and the T dependence of these coefficients and those previously reported at 298 K are obtained. This rate law model, used in conjunction with a relaxation matrix description of the Q‐branch spectrum, is shown to give good agreement with the observed, partially collapsed spectrum at 2.8 atm and 295 K.

COMPARISON OF ROTATIONAL RELAXATION RATE LAWS TO CHARACTERIZE THE RAMAN Q-BRANCH SPECTRUM OF CO AT 295 K

Abstract We test the ability of the energy corrected sudden (ECS), modified exponential gap (MEG) and the statistical power-exponential gap (SPEG) rate laws to characterize line broadening and line interference in the CO Q-branch at 295 K. All three rate laws fit the experimental linewidth data. The ECS law is found to predict too much spectral collapse. The MEG and SPEG laws both adequately model spectral collapse, but with different implications about the role of dipolar and quadrupolar symmetry forces in CO:CO line broadening. From semiclassical calculations of CO linewidths, we conclude that the SPEG law with a restriction to even ΔJ changes is the more physically correct model.

Measurement and rate law analysis of D2Q‐branch line broadening coefficients for collisions with D2, He, Ar, H2, and CH4

Continuous‐wave stimulated Raman spectroscopy has been used to obtain high resolution vibrational Q‐branch spectra at room temperature for pure D2 and D2:He, D2:H2, D2:Ar, and D2:CH4 mixtures. Measurements have been made for J=0–5 in the density region of 0.5–20.0 amagat, from which line broadening coefficients have been determined. These coefficients have been analyzed using a modified exponential energy gap rate law to identify the contributions of rotationally inelastic collisions and vibrational dephasing collisions to the linewidth. This analysis has assumed that vibrational dephasing is independent of rotational state, in accord with available theoretical studies. Results are compared with experimental and theoretical work on H2, HD, and D2, thereby characterizing the contributions of rotationally inelastic and vibrational dephasing collisions to the line broadening coefficients as a function of both rotational level and collision partner.