W. Kiefer

Structural resonances observed in the Raman spectra of optically levitated liquid droplets

Structural resonances have been found in the Raman spectra of optically levitated liquid droplets of mixtures of water and glycerol. The observed resonances could be assigned by using the well-known Lorenz-Mie formalism. It was found that for the particular droplet under investigation quite high-order numbers (l = 8,9) of the natural modes of oscillation of a sphere play a dominant role. We describe the intensities of the resonances in the Raman spectrum particularly through the volume averaged internal field intensity. We show further that the internal angle-averaged electric field intensity is localized near, but not confined to, the sphere surface.

Structural investigations of copper doped B2O3–Bi2O3 glasses with high bismuth oxide content

Raman and infrared spectroscopy have been employed to investigate the 99.5%[xB2O3(1−x)Bi2O3]0.5%CuO glasses with different Bi/B nominal ratios (0.07⩽x⩽0.625) in order to obtain information about the competitive role of B2O3 and Bi2O3 in the formation of the glass network. The glass samples have been prepared by melting at 1100 °C and rapidly cooling at room temperature. In order to relax the structure, to improve the local order and to develop crystalline phases the glass samples were kept at 575 °C for 10 h. The influence of both Bi2O3 and CuO on the vitreous B2O3 network as well as the local order changes around bismuth and boron atoms in as prepared and heat treated samples was studied. Structural modifications occurring in heat treated samples compared to the untreated glasses have been observed.

A Cell for Resonance Raman Excitation with Lasers in Liquids

The experimental observation of the resonance Raman effect in solutions with laser excitation is restricted by the absorption of the sample. Due to the thermal lens effect it is not possible to get a sharp laser focus in highly absorbing media. Under ordinary circumstances one is required to compromise between absorption and emission of the scattered light—that means discovering optimal solution concentrations and suitable laser power or focusing conditions to get the smallest degradation of the laser beam.

The UV-laser excited resonance raman spectrum of the I−3 ion☆

Abstract Solutions of cesium tri-iodide and potassium iodide and iodine in water show a strong resonance Raman effect of the I−3 ion when excited by the ultraviolet lines at 3638 and 3511 A of an argon ion laser, High intensity overtone progressions of the “symmetric” vibration νi were observed. This progression allows the confirmation of the presence of the I−3 ion in iodine-methanol solutions.

Vibrational spectroscopy of highly iron doped B2O3-Bi2O3 glass systems

Abstract Glass systems of composition 95%[xB2O3(1−x)Bi2O3]5%Fe2O3 with different Bi/B nominal ratios (0.07⩽x⩽0.90) have been investigated by means of Raman and infrared spectroscopy in order to obtain information about the competitive role of B2O3 and Bi2O3 in the formation of the glass network. The glass samples have been prepared by melting at 1100 °C and rapidly cooling at room temperature. The samples have been further kept at 575 °C for 10 h in order to relax the glasses structure as well as to improve the local order and to develop the new formed crystalline phases. The influence of both Bi2O3 and Fe2O3 on the vitreous B2O3 network as well as the local order changes around bismuth and boron atoms in as prepared and heat-treated samples have been studied. Structural modifications occurring in the heat-treated samples compared to the untreated glasses have been pointed out.

Femtosecond time-resolved coherent anti-Stokes Raman scattering for the simultaneous study of ultrafast ground and excited state dynamics" iodine vapour

Abstract Femtosecond time-resolved coherent anti-Stokes Raman scattering (CARS) is applied in order to investigate molecular dynamics in the gas phase. As model system iodine vapour is chosen. By changing the timing of the laser pulses of this non-degenerate four-wave mixing technique, the wavepacket motion on both the electronically excited and the ground states can be detected as oscillations in the coherent anti-Stokes signal. Different decay times are found for the amplitudes of the excited and ground-state beats. The results are compared with transients obtained from a conventional pump-probe technique, where laser-induced fluorescence is used for detection.

Raman-Microsampling Technique Applying Optical Levitation by Radiation Pressure

We report on a new Raman microprobe technique where micron-sized solid particles are trapped in stable optical potential wells using only the force of radiation pressure from a continuous gas laser. We demonstrate this technique with Raman spectra from spherical and non-spherical particles of sizes ranging between 10–30 μm. The particles are stably supported by a vertical directed focused TEM00-mode cw argon ion laser of ∼500 mW. The latter simultaneously serves as the exciting light source. Several suggestions for improvements of this technique are made.

Kinetic investigations of hydrolysis and condensation of the glycidoxypropyltrimethoxysilane/aminopropyltriethoxy-silane system by means of FT-Raman spectroscopy I

Abstract Fourier transform Raman spectra with laser excitation in the near infrared were recorded during the base-catalyzed sol–gel reaction of the system 3-glycidoxypropyl-trimethoxysilane (GPTS)/3-aminopropyl-triethoxysilane (APTS). This combination of organo-(alkoxy)silanes is used for the synthesis of hybrid polymers. Raman bands of the trimethoxysilyl- and the epoxy-moieties were used to monitor the kinetic behaviour of the hydrolysis reaction and the ring cleavage as a function of temperature. A decrease of the rate of hydrolysis of GPTS at elevated temperatures is attributed to a decrease of the pH caused by temporarily accumulating silanol groups. After the start of the condensation reactions, the pH increases and forces hydrolysis to accelerate. The results indicate the existence of a pentacoordinated transition state with a negative charge at the silicon atom during base catalyzed hydrolysis.

Rotating Raman Sample Technique for Colored Crystal Powders; Resonance Raman Effect in Solid KMnO4

A simple sample technique which makes it possible to record Raman spectra of highly absorbing solids is described. The main feature is a rotating sample system containing pressed crystal powders, on which the laser beam is focused. The relative motion between laser focus and sample surface avoids heating and decomposition of the crystal powder. With this technique it is, for instance, possible to obtain a Raman spectrum of solid potassium permanganate, displaying a progression of strongly resonance enhanced overtones of the totally symmetric permanganate mode as well as a well-defined weakly enhanced spectrum for the other internal modes.

The resonance Raman effect of the permanganate and chromate ions

Resonance Raman spectra have been obtained from the MnO4 - and CrO4 2- ions in aqueous solutions and as solid. High intensity overtone progressions of the totally symmetric vibration v 1 were observed, allowing estimates of the anharmonicity constants and harmonic frequencies to be made for the v 1 breathing mode. Relative intensities have been measured in the resonance case and correlated with the absorption spectra. Also preresonance intensity data for CrO4 2- have been determined and discussed in terms of an existing theory. The overtone progression of v 1 shows a large increase in half-bandwidth with increasing vibrational quantum number.