Search results for "RADIATION"
showing 10 items of 5298 documents
Comparison of thermal‐ and photo‐polymerization of lauryl methacrylate monolithic columns for CEC
2009
Lauryl methacrylate-based (LMA) monolithic columns for CEC, prepared using either thermal initiation or by UV-irradiation in the presence of AIBN have been compared. Thermal polymerization was carried out at 70 degrees C for 20 h. For UV initiation, the effects of the time exposure to UV light and irradiation energy were investigated. For each initiation process, the influence of composition of porogenic solvent (1,4-butanediol/1-propanol ratio) on the physical and electrochromatographic properties of the resulting monoliths was also evaluated. Photochemically lauryl methacrylate stationary phases initiated showed higher permeabilities and better efficiencies than those prepared by thermal …
Experimental Investigations and Ab Initio Studies of Tellurium(II) Dithiolates, Te(SR)2
1999
The reaction between Te(O(i)Pr)(4) and HSR offers a new and effective route to tellurium dithiolates, Te(SR)(2). Te(S(i)Pr)(2) (1) and Te(S(t)Bu)(2) (2) are stable compounds whereas Te(SPh)(2) (3) slowly decomposes at room temperature to give Te and Ph(2)S(2). IR spectra of 1-3 and ab initio calculations (HF/3-21G(d) and MP2 with double-zeta polarization effective core potential basis set) show nu(as)(Te-S) and nu(s)(Te-S) to be around 340 and 380 cm(-)(1), respectively. UV spectra exhibit similar lambda(max) (346-348 nm) for all three compounds, with the greater extinction coefficient of 3 accounting for its different and more intense color. Analysis of the molecular orbitals of the model …
Experimental evidence of E’_gamma centers generation from oxygen vacancies in a-SiO2
2007
Abstract We report on the thermal treatment effects in a γ-ray irradiated oxygen deficient amorphous silicon dioxide (a-SiO2) containing Al impurities. We observed that by thermal treatments the intensity of the 7.6 eV optical absorption band, associated to an oxygen deficient center, and the EPR signal amplitude of irradiation induced [AlO4]0 centers gradually decrease. During these thermal treatments, the E γ ′ centers concentration is found to increase in a correlated way to the decrease of the 7.6 eV absorption amplitude. These results are interpreted assuming an hole-transfer process from the [AlO4]0 centers to the diamagnetic oxygen vacancies, resulting in the generation of E γ ′ cent…
Anomalous Kinetics of Diffusion-Controlled Defect Annealing in Irradiated Ionic Solids
2017
The authors thanks A. Ch. Lushchik, M. Izerrouken, and V. Lisitsyn for stimulating discussions. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euroatom research and training programme 2014-2018 under Grant Agreement No. 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. R.V. acknowledges the financial support by the MEIC (Ministerio de Economa, Industria y Competitivad; Project ENE2015-70300-C3-1-R). The calculations were performed using facilities of the Stuttgart Supercomputer Center (Project DEFTD 12939).
Experimental evidence for two different precursors of Eγ′ centers in silica
2004
Abstract Electron paramagnetic resonance measurements of concentration and line shape of E γ ′ centers induced by γ ray irradiation are presented for natural and synthetic commercial silica with different OH contents. Synthetic materials with OH content >200 ppm by weight show one line shape for all investigated doses. In contrast, the other materials show a different line shape at low irradiation doses. Differences are also observed in the concentration growth of the E γ ′ centers in synthetic wet materials and in the other materials. The results are interpreted as evidence of two E γ ′ centers distinguishable by their line shape and having different precursors.
On the relaxation mechanisms of 6-azauracil
2011
The nonadiabatic photochemistry of 6-azauracil has been studied by means of the CASPT2//CASSCF protocol and double-ζ plus polarization ANO basis sets. Minimum energy states, transition states, minimum energy paths, and surface intersections have been computed in order to obtain an accurate description of several potential energy hypersurfaces. It is concluded that, after absorption of ultraviolet radiation (248 nm), two main relaxation mechanisms may occur, via which the lowest (3)(ππ*) state can be populated. The first one takes place via a conical intersection involving the bright (1)(ππ*) and the lowest (1)(nπ*) states, ((1)ππ*/(1)nπ*)(CI), from which a low-energy singlet-triplet crossin…
Resonance ionization spectroscopy of fermium (Z=100)
2003
Laser spectroscopy has been applied for the first time to measure resonant transition frequencies of fermium (Zs 100). A number of 2.7=10 atoms was electrodeposited on a Ta filament and covered with a 1 mm Ti layer. Fm 10
Three-dimensional orientational colocalization of individual donor--acceptor pairs.
2004
We report on the determination of the three-dimensional orientation of the donor and acceptor transition dipoles in individual fluorescence resonance energy transfer (FRET) pairs by means of scanning optical microscopy with annular illumination. Knowledge of the mutual orientation of the donor and acceptor dipole is mandatory for reliable distance determination based on FRET efficiency measurements. In our model system perylenediimide as the donor and terryelenediimide as the acceptor are coupled via a stiff p-terphenyl linker. The absorption dipoles of the donor and acceptor are selectively addressed by the 488 nm and 647 line of an Ar/Kr mixed gas laser, respectively. A clear deviation fr…
Enhanced nonlinear optical properties and thermal stability of donor-acceptor substituted oligothiophenes
1997
Abstract Linear and nonlinear optical properties of a series of novel donor-acceptor substituted α-oligothiophenes were investigated by means of electrooptical absorption measurements (EOAM) and electric field induced second harmonic generation (EFISH). The second-order polarizabilities β(−2ω; ω, ω) were related to dipole changes Δμ ag and transition dipoles μ ag associated with low-lying charge-transfer (CT) excitations by using the perturbational two-level approximation. Systematic variation of the donor and acceptor groups led to compounds with exceptional nonlinearity and thermal stability. Too strong donor/acceptor pairs, however, yielded structures in the charge-resonance (CR) limit w…
Vibrational effects in Na2( , v′)+Na(3p3/2) associative ionization
1999
Abstract Associative ionizing Na2( A 1 Σ + u , v′)+Na(3p3/2) collisions have been studied in a single supersonic beam with respect to the influence of the initial vibrational excitation of the molecules on the reaction efficiency. An enhancement of trimer ion yield of nearly one order of magnitude has been observed as the vibrational excitation increases from v′=0 to v′=14.