Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userLow-temperature Raman spectra of L-histidine crystal
408
0
0.0
(
0
)
Added by
Gardenia Pinheiro Sousa
Publication date
2013
fields
Physics
and research's language is
English
Authors
G. P. De Sousa
Ask ChatGPT about the research
No Arabic abstract
We present a Raman spectroscopy investigation of the vibrational properties of L-histidine crystals at low temperatures. The temperature dependence of the spectra show discontinuities at 165 K, which we identify with modifications in the bonds associated to both the NH3+ and CO2- motifs indicative of a conformational phase transition that changes the intermolecular bonds. Additional evidence of such a phase transition was provided by differential scanning calorimetry measurements, which identified an enthalpic anomaly at ~165 K.
rate research
Read More
Single crystal samples of L-leucine, C6H13NO2, a fundamental aliphatic amino acid of the human body, have been studied by Raman spectroscopy at temperatures from 300 to 430 K over the spectral range from 50 to 3100 cm-1. A tentative assignment of all bands is given. For high temperatures, several modifications on the Raman spectra were observed at about 353 K, giving evidence that the L-leucine crystal undergoes a structural phase transition.
Charge transfer multiplet (CTM) theory is a computationally undemanding and highly mature method for simulating the soft X-ray spectra of first-row transition metal complexes. However, CTM theory has seldom been applied to the simulation of excited state spectra. In this article, we extend the CTM4XAS software package to simulate M2,3- and L2,3-edge spectra of excited states of first-row transition metals and to interpret CTM eigenfunctions in terms of Russell-Saunders term symbols. We use these new programs to reinterpret the recently reported excited state M2,3-edge difference spectra of photogenerated ferrocenium cations and propose alternative assignments for the electronic state of the photogenerated ferrocenium cations supported by CTM theory simulations. We also use these new programs to model the L2,3-edge spectra of FeII compounds during nuclear relaxation following photoinduced spin crossover, and propose spectroscopic signatures for their vibrationally hot states
Chromium thiophosphate (CrPS4), a monoclinic crystal of C_2^3 space group, is a ternary layered semiconductor with an optical bandgap of 1.4 eV and exhibits antiferromagnetism below 36 K. Despite its potential in optoelectronic and magnetic applications, the symmetry of its lattice vibrations has not been systematically studied. In this work, we performed a polarized Raman spectroscopy of bulk CrPS4 using three different excitation wavelengths of 457, 514, and 633 nm. High-quality crystals grown by the chemical vapor transport method were mechanically exfoliated or polished to expose three orthogonal crystallographic facets. Polarized Raman spectra were obtained in parallel and cross configurations by rotating samples about the surface normal to each of the facets. Among 33 Raman active modes (16 A and 17 B) at the Brillouin zone center, 19 (8) peaks observed in the parallel (cross) configuration were assigned as A (B) modes. Complex-valued Raman tensors were determined for 7 major A modes using the angle-dependent Raman spectra of the three facets. The results can also be used in determining the crystallographic orientations of CrPS4 unequivocally.
{gamma}-graphdiyne is a 2D carbon structure beyond graphene: it is formed by sp and sp2 carbon atoms organized as hexagonal rings connected by linear links, and it is predicted to be a semiconductor. The lateral confinement of {gamma}-graphdiyne nanoribbons significantly affects the electronic and vibrational properties. By means of periodic Density Functional Theory (DFT) calculations we investigate here the electronic band structure, the Raman and IR spectra of the {gamma}-graphdiyne 2D crystal and related nanoribbons. We discuss the effect of the functional and basis set on the evaluation of the band gap, highlighting the reliability of hybrid functionals. By joining DFT calculations with a symmetry analysis, we assign in detail the IR and Raman spectra of {gamma}-graphdiyne. On this basis we show the modulation of the gap in nanoribbons of increasing width and different edges (armchair, zigzag). We assess how confinement affects the Raman and IR spectra of such nanoribbons by comparing their vibrational modes with the phonons of the parent 2D crystal. Our symmetry-based classification allows identifying the marker bands sensitive to the edge structure and lateral confinement of nanoribbons of increasing width. These results show the effectiveness of vibrational spectroscopy for the characterization of such nanostructures.
The crystal structure of the new superconductor UTe2 has been investigated for the first time at low temperature (LT) of 2.7 K, just closely above the superconducting transition temperature of about 1.7 K by single crystal neutron diffraction, in order to prove, whether the orthorhombic structure of type Immm (Nr. 71 Int. Tabl.) reported for room temperature (RT) persists down to the superconducting phase and can be considered as a parent symmetry for the development of spin triplet superconductivity. Our results show that the RT structure reported previously obtained by single crystal X-Ray diffraction indeed describes also the LT neutron diffraction data with high precision. No structural change from RT down to 2.7 K is observed. Detailed structural parameters for UTe2 at LT are reported.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
