G. Turrell

Raman spectroscopic investigation of the dynamics of urea–water complexes

The hydration of urea via hydrogen‐bond formation was found to have a significant effect on the observed Raman band shapes. An analysis indicates that, on the average, one molecule of water is carried along with a solute molecule during its reorientational motion (τR≊2.5 ps). Vibrational dephasing of the ν4 vibration (τω≊0.2 ps) is independent of concentration and appears to decrease slightly with increasing temperature. No evidence of urea dimer formation was detected.

The Raman Effect

Publisher Summary This chapter discusses the Raman effect which results from the interaction of vibrational and rotational motions of molecules with electromagnetic radiation. Brillouin scattering involves the translational motion of molecules in liquids and solids. A simple classical picture of the Raman effect can be obtained by analogy with the amplitude modulation of a radiofrequency carrier wave by an audio signal. The resulting sidebands are similar to the Raman spectrum produced by the combination of the frequencies of molecular vibrations with the frequency of the laser excitation. However, for most purposes, a quantum mechanical model is more useful. The interaction of a molecule with electromagnetic radiation can thus be analyzed in terms of an energy-transfer mechanism. The simplest absorption process involves the gain of a quantum of energy by the molecule, accompanied by the annihilation of a quantum of light or photon. Similarly, spontaneous emission can be described as the creation of one or more photons due to the corresponding loss in molecular energy. The “excitation profile” in resonance Raman spectroscopy describes the intensity of Raman scattering as a function of the frequency of the excitation.

Infrared and Raman spectra of hexaborides: force-field calculations, and isotopic effects☆

Abstract The vibrational spectra of cubic crystals of lanthanide hexaborides, MB 6 , are interpreted with the aid of a force-field calculation. The effects of the naturally occurring 10 B and 11 B isotopes are analyzed and the consequent spectral features identified.

Characteristics of Raman Microscopy

Publisher Summary This chapter focuses on those characteristics which differentiate Raman microspectroscopy from the more conventional techniques. The important characteristics of Raman microscopy are directly related to two fundamental optical considerations: (1) the focusing of the incident laser excitation on the sample and (2) the collection of the scattered light. The chapter analyzes the specific problem of coupling a microscope to a Raman spectrometer. The confocal effect is described, as it the basis of recent advances in Raman instrumentation, including imaging techniques. The total Raman intensity depends on the solid angle Ω in which the scattered light is collected. In the backscattering configuration Ω describes approximately the cones of both the incident and scattered light. The optimum use of the Raman light flux o collected from a sample requires it to be transmitted from sample to detector via the successive apertures of the instrument. The invariance conditions of the optical extent can be fulfilled with the use of coupling optics which result in good matching between all of the apertures along the entire light path, from microscope to the spectrometer detector.

Effect of pressure on the infrared absorption band HCl in CCl4 solution

Abstract The infrared absorption of HCl in CCl 4 solution has been investigated at pressures up to 6kbar. The experimental band shapes have been analyzed to yield band moments and the autocorrelation function for reorientational movement of the solute molecule. The second moment is found to decrease with increasing pressure while the torque acting on the HCl solute increases slightly.

Conformational stability of some branched octanes

Abstract Conformational analyses have been made of the series of branched octanes 2,2,3- 2,2,4- 2,3,3- and 2,3,4-trimethyl pentane. The energies and structures of these isomers have been determined. It is shown that the most stable configurations of the carbon skeletons of these branched isomers do not necessarily correspond to the all- trans configurations, as does their normal homologue.

Infrared spectroscopic investigation of the effect of temperature on the ν3 band shapes of CO2 and N2O in some liquid alkanes

Abstract Infrared spectra are presented of the ν 3 vibrations of CO 2 and N 2 O dissolved in two isomeric octanes, n -octane and 2,2,4-trimethyl pentane. In each case the central absorption feature decreases in height with increasing temperature, while the band width increases accordingly. The profiles of the absorption bands are analyzed to yield the autocorrelation functions, correlation times and band moments.

Polarization measurements in micro-Raman and microfluorescence spectrometries

Abstract The depolarization ratios of the Raman and resonance Raman bands of both isotropic and anisotropic samples performed with micro-Raman spectrometers are in good agreement with those obtained with conventional instruments, provided that corrections are made for the effects of the beam splitter and the high numerical aperture objectives. The polarization measurements have been extended to microfluorescence spectrometry and correct results are obtained.

Raman Microscopy and Other Local Analysis Techniques

Publisher Summary This chapter focuses on Raman microscopy and other local analysis techniques. In Raman microspectrometry, two main questions must be considered: (1) how to localize the area to be analyzed, and (2) how to analyze the area in question. To localize an area as small as 0.5-0.25 mm in size, the human eye is sufficient, but when the area is smaller than 0.25 mm, an optical system which is capable of delivering a magnified and contrasted image to the eye is necessary. To analyze the area of interest the analytical system may be the same as that employed in the imaging technique, or quite different. In general, the two main characteristics of imaging and analyzing are related. These are the lateral resolving power or lateral image resolution and the axial resolution or depth of field. The lateral resolving power takes into account the lower limit for the human eye, which is approximately 0.25 mm; this condition defines the necessary magnification and the smallest area to be localized at the sample surface. The axial resolution together with lateral resolution determines the analyzed volume. It depends not only on the optical characteristics of the system, but also on the nature of the sample. The chapter summarizes some of the basic features of electron optics and also reviews the coupling of Raman and electron microscopies.

Raman spectroscopic investigation of the vibrational and reorientational relaxation of CS2 in liquid carbon tetrachloride

The polarized and depolarized Raman spectra of the symmetrical stretching mode of CS2 in solution in CCl4 were measured over the mole‐fraction range 0.25 to 0.05. The autocorrelation functions for the vibrational and orientational motions of CS2 were calculated from the observed band shapes. The vibrational motion is less sensitive to concentration than is the reorientational one. At infinite dilution the orientational correlation time τ2R is approximately equal to 6.8 ps.