Search results for " Optics"
showing 10 items of 5880 documents
Time-resolved luminescence and induced absorption in PbWO4
1997
Abstract Luminescence and short-lived induced absorption are studied for two undoped PbWO4 crystals. Luminescence decay at LNT is delayed relative to irradiation pulse. The delay observed is either due to reabsorption of luminescence or due to creation of luminescence center excited states via energy or/and charge transfer after irradiation pulse. Short-lived absorption is observed within 1.1–3.6 eV spectral region at LNT as well as at RT. It is proposed that the short-lived absorption band peaking at ~ 3.5 eV is intrinsic.
Structural and spectroscopic study of the Br2...3-Br-pyridine complex by DFT calculations.
2007
Abstract The structure and the Raman vibrational spectrum of the complex Br 2 ⋯3-Br-pyridine are determined by DFT calculations using different parametrizations. The calculations are performed taking into account the effects of the dichloromethane as solvent by the CPCM method. A value of 39 kJ mol −1 for the formation enthalpy and of 1 kJ mol −1 for the formation free energy at room temperature in presence of the solvent is found. The predicted Raman spectrum is compared with the experimental one and the essential features of the spectrum are well reproduced by the B3LYP parametrization. The intensity changes of the bands when going from the free moieties to the complex are also generally …
Thermal effects on small para-hydrogen clusters
2010
A brief review of different quantum Monte Carlo simulations of small (p-H2)N clusters is presented. The clusters are viewed as a set of N structureless p-H2 molecules, interacting via an isotropic pairwise potential. Properties as superfluidity, magic numbers, radial structure, excitation spectra, and abundance production of (p-H2)N clusters are discussed and, whenever possible, a comparison with 4HeN droplets is presented. All together, the simulations indicate that temperature has a paradoxical effect of the properties of (p-H2)N clusters, as they are solid-like at high T and liquid-like at low T, due to quantum delocalization at the lowest temperature. © 2010 Wiley Periodicals, Inc. Int …
Triple-resonance autoionization of uranium optimized for diode laser excitation
2007
Abstract The photoionization of uranium via three-step excitation has been optimized for isotope selective trace analysis. A search found 13 new J = 6, 7, and 8 odd-parity states in the 36,850–37,200 cm− 1 region that allow blue–red–red three-photon excitation at wavelengths favorable for commercial diode laser systems. From each of these 13 states, near-threshold autoionization spectra were recorded at a resolution of 3 × 10− 4 cm− 1. Some 30 even-parity autoionizing levels with J = 5 to 9 have also been observed and characterized. Comparison of the spectra allows J assignment for the new intermediate levels as well as selection of an optimized path for trace analysis. We show that, for a …
Solvatochromy and symmetry breaking in two quadrupolar oligophenylenevinylenes
2020
Electrooptical absorption measurements (EOAM), solvatochromic dependences and quantum chemical simulations testify to large dipole moments change of two quadrupolar oligophenylenevinylenes upon transition to Franck-Condon excited state μeFC. The values of the dipole moments μg and μeFC are in the range [(4.2 - 4.9)1030] C m and (30.8 - 47.0)1030C m, respectively. The relations of dipole moments in the ground and excited states determined by EOAM correlate well with results obtained via the solvatochromic method. Calculations carried out by density functional theory (DFT) show that optimized configuration of the ground state of these molecules is not planar. The results from all methods appl…
Oxygen K-edge XANES investigation of NicMg1−cO solid solutions
2005
A series of Ni(c)Mg(1-c)O solid solutions are characterized by means of synchrotron radiation X-ray diffraction and X-ray absorption near-edge-structure spectroscopy at oxygen K-edge (532 eV). A dramatic drop of the pre-edge peak intensity is observed in the Ni(c)Mg(1-c)O system upon dilution. It can be attributed to a decrease of 3d(8)(Ni(2+))-2p(O(2-)) mixing upon dilution with magnesium ions due to a decrease of the number of 3d vacancies as nickel ion is replaced by magnesium ion. Similarly, the decrease of the number of 4s and 4p vacancies also leads to a decrease of 4s4p(Ni(2+))-2p(O(2-)) hybridization, and hence a drop of intensities of features B and C. The features E and F are more…
Using theozymes for designing transition-state analogs for the intramolecular aldol reaction of δ-diketones
2001
Two theozymes for the intramolecular aldol reaction of δ-diketones have been studied using ab initio methods. The presence of both acid/base residues favors several steps of the aldol reaction. The appropriate positioning of these residues can accelerate one of two diastereromeric reaction pathways, the catalyzed aldol reaction being highly stereoselective. Analysis of the geometrical parameters, charge distribution, and the shape of molecular electrostatic potential for the corresponding acid/base catalyzed transition structure allows us to design adequate transition-state analogs to favor a reactive channel of this intramolecular aldol reaction. © 2001 John Wiley & Sons, Inc. Int J Quant …
Montecarlo calculation of the structure of liquid acetonitrile
1992
Abstract A Montecarlo calculation of the structure of liquid acetonitrile, based on a Lonnard-Jones ab initio potential, has been performed. Pair correlation functions between all the heavy atoms are obtained for distances within 8 A°. The features of the obtained structure are discussed.
Comparison of electron diffraction data from non-linear optically active organic DMABC crystals obtained at 100 and 300 kV
2000
During the recent past, we have synthesized a new class of molecules with intramolecular two-dimensional charge transfer upon excitation. The present report presents such a molecule, 2,6-bis(4-dimethylamino-benzylidene)-cyclohexanone (DMABC), with an unusually high value of the second-order non-linear optical (NLO) coefficients. In order to optimize the macroscopic NLO properties of the compounds, it is necessary to relate their first hyperpolarizability tensors at a molecular level to those at a crystal bulk level. This requires a complete structure determination and refinement. However, the growth of sufficiently large single crystals, which are needed for structural analysis and refineme…
Direct observation of the electroadsorptive effect on ultrathin films for microsensor and catalytic-surface control.
2013
Microchemical sensors and catalytic reactors make use of gases during adsorption in specific ways on selected materials. Fine-tuning is normally achieved by morphological control and material doping. The latter relates surface properties to the electronic structure of the bulk, and this suggests the possibility of electronic control. Although unusual for catalytic surfaces, such phenomena are sometimes reported for microsensors, but with little understanding of the underlying mechanisms. Herein, direct observation of the electroadsorptive effect by a combination of X-ray photoelectron spectroscopy and conductivity analysis on nanometre-thick semiconductor films on buried control electrodes …