Search results for "Spectroscopy"
showing 10 items of 10293 documents
Time resolved CARS measurements of I2 in solid Kr
2006
Dephasing is a central concept in condensed phase spectroscopy. It determines how long a system will maintain its coherence. The dephasing time of a system is determined by dynamic intermolecular interactions, and therefore measurements of dephasing time can provide information on interactions and couplings between a molecule and its environment. This chapter illustrates the application of the femtosecond coherent anti-Stokes Raman scattering (CARS) method to investigate the vibrational dephasing of I 2 in solid krypton. Dephasing of vibrational states between v = 2 and v = 16 is studied in the temperature range T = 2.6–32 K. The low vibrational states show dephasing times on the order of a…
Monte Carlo Study of Dense Monolayer and Bilayer Films on the (100) Plane of Face-Centered Cubic Crystals
1999
A Monte Carlo simulation method in the canonical and in the grand canonical ensembles is used to study the behavior and properties of dense monolayer and bilayer films formed on the (100) plane of model face-centered cubic crystals. Systems with different effects due to the periodicity of the gas−solid potential are considered, and the mechanism of melting in the first and the second adsorbed layer is discussed. It is demonstrated that the film structure is very sensitive to the gas−solid potential corrugation, as well as to the temperature and the surface coverage. In particular, it is shown that monolayer films formed on weakly corrugated surfaces exhibit the incommensurate (dense) phase …
β-process of supercooled o-terphenyl: a comparison of dielectrical and NMR data guided by mode-coupling theory
1990
Abstract According to predictions of mode-coupling theory of the liquid-glass transition, a Cole-Cole dynamical susceptibility is applied to the β-relaxation of supercooled o -terphenyl as studied by 2 H NMR spin-lattice relaxation and by dielectrical relaxation. A temperature-dependent amplitude (1- f ) is assumed for the β-process which yields a description of the NMR data consistent with the dielectrical data. The plateau value f separating the α- and β-processes in the two-step correlation function reveals a similar temperature dependence as compared to the Debye-Waller factor.
Two-phonon magneto-Raman scattering in quantum wells: Fröhlich interaction
1996
We have developed a theoretical model of two-phonon resonant magneto-Raman scattering in a semiconductor quantum well (QW). Frohlich electron-phonon interaction has been considered and the corresponding selection rules are derived for Faraday geometry and backscattering configuration. The resonant profiles are analyzed as a function of magnetic field and laser energy. To simplify the discussion a three-band model with parabolic masses has been used as a first approach, studying later the role of heavy-hole light-hole admixture in the scattering process. It is shown that, due to mixing effects, Frohlich interaction contributes to the two-phonon Raman spectra in the parallel (z(σ ± , σ ± ) z)…
Two-LO-Phonon Resonant Raman Scattering in II-VI Semiconductors
1996
Recently, absolute values of socond-order Raman scattering efficiency have been measured around the E 0 and E 0 + Δ 0 critical points of several II-VI semiconductor compounds. The measurements were perfomed in the z(x,x)z backscattering configuration on (001) (ZnSe and ZnTe) and (110) (CdTe) surfaces. They show strong incoming and outgoing resonances around the baud gap and larger scattering efficiencies as compaered to III-V compounds. A theoretical model which includes excitons as intermediate states in the Raman process is shown to give a very good quantitative agreement between theory and experiment. Only a small discrepancy exists, while III-V compounds the discrepancies were close to …
Investigation of lattice dynamical and dielectric properties of MgO under high pressure by means of mid- and far-infrared spectroscopy.
2013
We investigate the lattice dynamical and dielectric properties of MgO single crystals and powders by measurements in the mid- and far-infrared frequency region under high pressures, ranging up to 21.7 GPa. The shift of the restrahlen region is used to determine the pressure dependence of the transverse and longitudinal optical modes. The analysis of the refractive index in the mid- and far-infrared region allowed us to obtain the pressure behavior of the static and electronic dielectric constants. The transverse effective charge slowly decreases under high pressure, reflecting the stability of MgO. As a consequence, the pressure dependence of the static and electronic dielectric constants i…
Spin-polarization effects for electrons passing through thin iron and cobalt films
1993
Abstract Spin-dependent effects of the inelastic mean free path (IMFP) are evident for low-energy electrons passing through magnetized ferromagnetic films caused by a different attenuation within the layer. Values of IMFP for both spin components were determined for ultrathin iron and cobalt layers on W(1 1 0) by means of spin-resolving photoelectron spectroscopy.
Evaluation of the electrochemical anion recognition ofNO3−-imprinted poly(Azure A) inNO3−/Cl−mixed solutions by ac-electrogravimetry
2016
Abstract During the reversible electrochemical reactions of the intrinsically conducting polymer (ICP) films, ions are inserted in them to balance the inner charge site of the polymer. For this reason, doped ICP films with anions or cations can be good candidates for the electrochemical removal of contaminant ions from wastewater. In this work, a polymer of a phenothiazine derivative (poly(Azure A or PAA)) was electrosynthesized by cyclic voltammetry in aqueous solutions using nitrate ions as a structural template. After that, PAA film was repeatedly cycled in identical conditions in a monomer-free solution. The electrochemical anion recognition of the nitrate-imprinted poly(Azure A) ( N O …
An approach to the electrochemical activity of poly-(phenothiazines) by complementary electrochemical impedance spectroscopy and Vis–NIR spectroscopy
2010
Abstract The electroactivity of two poly-(phenothiazine), the poly-(Azure A) and the poly-(Methylene Blue), has been compared in this work. The spectroelectrochemical results prove clearly the existence of two electroactive moieties integrated in the polymeric lattice, the phenothiazine ring (detected by changes of absorbance at 590 and 685 nm) and the newly formed covalent links which fixes the monomers in the backbone of the polymer (detected by changes of absorbance at 460 and 875 nm). Differences in the electrochemical response of both polymers are due to differences in this covalent link. However in both polymers, the charge balance during electrochemical reactions takes place by the e…
Charge transport in electrically responsive polymer layers
2007
The processes of charge transport in the conducting polymer electrochromic films have been studied by means of spectral-electrochemical method, impedance spectroscopy and cyclic voltametry measurements. It has been shown that charge transport during the coloration-bleaching processes is not symmetric phenomenon. By means of impedance spectroscopy the effective diffusion coefficients for anode and cathode charge transport have been measured. The higher rate of charge transport in the bleaching process as compared to coloration is considered in the frame of conformation rebuilding of conducting polymer chains.