Search results for "Solid-state"
showing 10 items of 530 documents
Magnon and Phonon Excitations in Nanosized NiO
2019
Single-crystal, microcrystalline and nanocrystalline nickel oxides (NiO) have been studied by Raman spectroscopy. A new band at ~200 cm-1 and TO-LO splitting of the band at 350–650 cm-1 have been found in the spectra of single-crystals NiO(100), NiO(110) and NiO(111). The Raman spectra of microcrystalline (1500 nm) and nanocrystalline (13–100 nm) NiO resemble those of the single crystals. They all contain the two-magnon band at 1500 cm-1, indicating that the oxides remain at room temperature in the antiferromagnetic phase. Besides, a new sharp Raman band has been observed at 500 cm-1 in nanocrystalline NiO. Its temperature dependence suggests the magnetic origin of the band, possibly associ…
In vitro evaluation of the temperature increment at the external root surface after Er,Cr:YSGG laser irradiation of the root canal
2009
Objectives. A study was made to determine the temperature increment at the dental root surface following Er,Cr:YSGG laser irradiation of the root canal. Design. Human canines and incisors previously instrumented to K file number ISO 30 were used. Irradiation was carried out with glass fiber endodontic tips measuring 200 µm in diameter and especially designed for insertion in the root canal. The teeth were irradiated at 1 and 2 W for 30 seconds, without water spraying or air, and applying a continuous circular movement (approximately 2 mm/sec.) in the apico-coronal direction. Results. At the 1 W power setting, the mean temperature increment was 3.84ºC versus 5.01ºC at 2 W. In all cases the d…
Thermal increment due to ErCr: YSGG and CO2 laser irradiation of different implant surfaces. A pilot study
2010
Podeu consultar la versió en castellà http://hdl.handle.net/2445/118903
Inverted energy gap law for the nonradiative decay in fluorescent floppy molecules: larger fluorescence quantum yields for smaller energy gaps
2019
A data survey on experimental fluorescence quantum yields of (multi)substituted dicyano-distyrylbenzenes in fluid solution evidences that non-radiative decay increases with the Franck-Condon energy (E-FC), being opposite to the conventional energy gap law. Quantum-chemistry indicates that this is controlled by access to the conical intersection (CI) following the Bell-Evans-Polanyi principle as a first-step approximation for this family of molecules; the variations in E-FC among the different compounds are found to be decisive, while those of E-CI are estimated to be weaker or even enhancing the effect. The current findings may have significant consequences for the design of molecules for o…
Solid-State NMR, X-ray Diffraction, and Thermoanalytical Studies Towards the Identification, Isolation, and Structural Characterization of Polymorphs…
2009
Combined solid-state NMR, powder, and single crystal X-ray diffraction, as well as thermoanalytical studies were performed towards the identification, isolation, and structural characterization of ...
Systematic study of the physicochemical properties of a homologous series of aminobisphosphonates
2012
ABSTRACT: Aminobisphosphonates, e.g., alendronate and neridronate, are a well known class of molecules used as drugs for various bone diseases. Although these molecules have been available for decades, a detailed understanding of their most important physicochemical properties under comparable conditions is lacking. In this study, ten aminobisphosphonates, H2N(CH2)nC(OH)[P(O)(OH)2]2, in which n = 2-5, 7-11 and 15 have been synthesized. Their aqueous solubility as a function of temperature and pH, pKa-values, thermal stability, IR absorptions, and NMR spectral data for both liquid (1H, 13C, 31P-NMR) and solid state (13C, 15N and 31P-CPMAS NMR) were determined. Peer reviewed
Solid-state NMR and computational studies of tetratolyl urea calix[4]arene inclusion compounds.
2009
Solid-state guest dynamics of tetratolyl tetraurea calix[4]arene tetrapentylether dimeric capsules filled with different types of aromatic guests such as benzene-d6, fluorobenzene-d5 and 1,4-difluorobenzene were studied. Upon inclusion, all guest moieties revealed complexation-induced shifts varying from 2.8 ppm to 5.1 ppm. All guest molecules were shown to undergo distinct motions, ranging from mere C6-rotations of benzene-d6 to (ill-defined) 180 degrees phenyl flips of fluorobenzene-d5. In all cases, dynamic heterogeneities were identified based on 2H lineshape deconvolution. In addition, by combination of both a computed nucleus independent chemical shift (NICS) map and explicit 19F and …
Guest exchange in dimeric capsules of a tetraurea calix[4]arene in the solid state
2007
A solid powder of hydrogen bonded dimers of a tetraurea calix[4]arene is able to exchange the encapsulated guest in contact with the vapor of a second guest. The molecules of a guest-free powder obtained from a polar solvent cannot rearrange in the solid phase to form new guest-filled capsules under these conditions.
Precise measurement of 1H 90° pulse in solid-state NMR spectroscopy for complex and heterogeneous molecular systems
2007
The 90 degrees pulse calibration is essential in NMR spectroscopy to prevent artefacts in the liquid state or to enhance cross-polarization efficiency in the solid state. We verified pulse-angle (PA) errors due to circuit impedances in solid-state NMR and suggested a possible solution to prevent the inconvenience of PA errors. The classic pulse sequences used to calibrate (1)H 90 degrees pulse lengths by direct detection of protons or by cross-polarization were modified in order to replace single (1)H pulses with (1)H pulse trains. Pulse trains were found to decrease the effect of PA imperfections in the calibration of basic pulses (i.e. 90 degrees and 180 degrees ) for a number of organic …
Dynamics of guest molecules in PHTP inclusion compounds as probed by solid-state NMR and fluorescence spectroscopy.
2009
Partially deuterated 1,4-distyrylbenzene () is included into the pseudohexagonal nanochannels of perhydrotriphenylene (PHTP). The overall and intramolecular mobility of is investigated over a wide temperature range by (13)C, (2)H NMR as well as fluorescence spectroscopy. Simulations of the (2)H NMR spectral shapes reveal an overall wobble motion of in the channels with an amplitude of about 4 degrees at T = 220 K and 10 degrees at T = 410 K. Above T = 320 K the wobble motion is superimposed by localized 180 degrees flips of the terminal phenyl rings with a frequency of 10(6) Hz at T = 340 K. The activation energies of both types of motions are around 40 kJ mol(-1) which imply a strong steri…