Browsing by Tema "Absorption spectroscopy"

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Chromatographic and spectroscopic properties of regioisomers of some 1<i>H</i>‐1,5‐benzodiazepines
(Wiley, 1994) S. Vianna‐Rodrigues; L. Martins‐Viana; Jairo Quiroga; Braulio Insuasty; Rodrigo Abonı́a; W. Baumann
Abstract The separation of the two regioisomeric derivatives of 1 H ‐1,5‐benzodiazepine yielded from the reaction of 1,2‐diamino‐4‐methylbenzene with 4‐substituted acetophenones was performed by reversed phase high performance liquid chromatography, and the absorption spectra of the separated isomers have been determined for three isomer pairs which have been obtained starting from acetophenones with substituents of different electronegativity. The isomer ratio then could be estimated as well from the ratio of the peak areas as from the absorption spectra. They agree well with the known ratio determined from nmr intensities.
Effects of Fe Impurity in Vibrational Modes of CuInS<sub>2</sub>
(Institute of Physics, 1981) N.V. Joshi
Lattice dynamical behaviour of CuInS 2 with Fe impurity has been examined at 4.2 K by using Fourier transform spectroscopy. The observed modes are indentified. The mode located at 106 cm -1 is analysed by using a molecular model and was found to be originated by the Fe impurity at In sites. The peak situated at 155 cm -1 could not be explained with a one phonon excitation process and hence it is tentatively attributed to a two phonons absorption of the \varGamma 4 mode or a combination mode of two TO modes.
Naica’s “Cueva de los Cristales”: Synchrotron radiation characterization of the wall-crystal interface
(2022) Bernardo Pérez-Cázares; María E. Fuentes; L. Fuentes-Cobas; Isaí Castillo-Sandoval; Iván Jalil Antón Carreño-Márquez; Hilda E. Esparza-Ponce; Diane Eichert; René Loredo-Portales; Jesús Canche-Tello; José Manuel Nápoles-Duarte
Naica’s ”Cueva de los Cristales” was discovered in 2000. It has been considered particularly interesting for its beauty and the challenges it poses to crystallography. This article focuses on the study of the wall-selenite interface by various techniques, particularly X-ray diffraction (XRD), scanning electron microscopy (SEM), with emphasis on micro-X-ray fluorescence (micro-XRF) and micro-X-ray absorption near edge structure (micro-XANES). The main phases calcite, quartz, goethite and montmorillonite were identified by XRD, as well as the association of crystalline and amorphous minor and trace phases of Zn, Mn, Cu, As and Pb. The latter were identified in micro-XRF maps and micro-XANES spectra. The results for the morphology and the chemical description of the crystal-wall interface may contribute to propose a nucleation and growth mechanism for Naica megacrystals.
Theory of the Compensation-Induced Parity-Forbidden Excitation Spectra of Shallow Impurities in Semiconductors
(1974) Timothy Gonzalez; Luis R. González; J. Trylski
An approximate formula for the line shape for the compensation-induced parity-forbidden 1s–2s optical absorption of shallow hydrogen-like impurities in semiconductors is given in the limit of small compensations. The unusual “camel-back” structure of the absorption peak is predicted.