排序方式: 共有140条查询结果,搜索用时 46 毫秒
111.
D. Giulietti V. Biancalana D. Batani A. Giulietti L. Gizzi L. Nocera E. Schifano 《Il Nuovo Cimento D》1991,13(7):845-858
Summary Side emitted 3ω/2 radiation was studied by interacting 1.064 μm laser light with plasmas obtained from exploding thin foils.
Both focusing (f/8) and collecting (f/7) optics were designed in order to reduce the instrumental bandwidth of the 3ω/2 spectrum. Time-resolved spectra and time-resolved
images were obtained and analysed. All the observed spectral features, including the substantial lack of a ?blue? component,
the amount of red shift and bandwidth, are consistent with the Karttunen theory of half-integer harmonics generated in plasmas.
This theory takes into account the propagation of ω/2 plasmons produced by ?two plasmon decay? and their coupling with laser
light. 相似文献
112.
Vezenov DV Mayers BT Conroy RS Whitesides GM Snee PT Chan Y Nocera DG Bawendi MG 《Journal of the American Chemical Society》2005,127(25):8952-8953
This communication describes a long (1 cm), laser-pumped, liquid core-liquid cladding (L2) waveguide laser. This device provides a simple, high intensity, tunable light source for microfludic applications. Using a core solution of 2 mM rhodamine 640 perchlorate, optically pumped by a frequency-doubled Nd:YAG laser, we found that the threshold for lasing was as low as 22 muJ (16-ns pulse length) and had a slope efficiency up to 20%. The output wavelength was tunable over a 20-nm range by changing the ratio of solvent components (dimethyl sulfoxide and methanol) in the liquid core. 相似文献
113.
Three new redox-based, hydrothermal, synthetic methods have been developed for the preparation of a new series of jarosites, AV(3)(OH)(6)(SO(4))(2) (A = Na(+), K(+), Rb(+), Tl(+), and NH(4)(+)), in high purity and in single crystalline form. The V(3+) jarosites have been characterized by single-crystal X-ray and elemental analysis, and by infrared and electronic absorption spectroscopy. The synthetic methods employed here represent a new approach for the preparation of the jarosite class of compounds, which for the past several decades, have been notoriously difficult to prepare in pure form. To demonstrate the impact of our new synthetic techniques on the magnetic properties of jarosites, the V(3+) jarosites were also prepared according to the nonredox techniques used over the past 30 years. A comparative study of these samples and those prepared by our new synthetic methods reveals widely divergent magnetic properties, thus pointing to the importance of the new redox synthetic methods to future magnetism studies of jarosite compounds. 相似文献
114.
Daniel G. Nocera 《Journal of Cluster Science》1994,5(1):185-209
Quadruply bonded metal-metal (M4-M)comptexes in electronic excited stares exhibit a rich oxidation-reduction chemistry. The structural, electronic, and oxidation-reduction properties of M4-M complexes may be exploited to rationally design their excited state chemistry from conventional one-electron pathways to the first Iogical development of discrete multielectron pathways. As we commemorate the 30-year anniversary of the discovery of M4-M complexes by F. A. Cotton, this review shows that they currently provide chemistry with some of the most diverse and novel reactivity for transition metal complexes in the excited state. 相似文献
115.
Rhenium(I) polypyridyl complexes have been designed for the intramolecular photogeneration of tyrosyl radical. Tyrosine (Y) and phenylalanine (F) have each been separately appended to a conventional Re(I)(bpy)(CO)(3)CN framework via an amide linkage to the bipyridine (bpy) ligand. Comparative time-resolved emission quenching and transient absorption spectra of Re(bpy-Y)(CO)(3)CN and Re(bpy-F)(CO)(3)CN show that Y is oxidized only upon its deprotonation at pH 12. In an effort to redirect electron transport so that it is more compatible with intramolecular Y oxidation, polypyridyl Re(I) complexes have been prepared with the amide bond functionality located on a pendant phosphine ligand. A [Re(phen)(PP-Bn)(CO)(2)](PF(6)) (PP = bis(diphenylphosphino)ethylene) complex has been synthesized and crystallographically characterized. Electrochemistry and phosphorescence measurements of this complex indicate a modest excited-state potential for tyrosine oxidation, similar to that for the (bpy)Re(I)(CO)(3)CN framework. The excited-state oxidation potential can be increased by introducing a monodentate phosphine to the Re(I)(NN)(CO)(3)(+) framework (NN = polypyridyl). In this case, Y is oxidized at all pHs when appended to the triphenylphosphine (P) of [Re(phen)(P-Y)(CO(3))](PF(6)). Analysis of the pH dependence of the rate constant for tyrosyl radical generation is consistent with a proton-coupled electron transfer (PCET) quenching mechanism. 相似文献
116.
117.
ZnCu(3)(OH)(6)Cl(2) (S=1/2) is a promising new candidate for an ideal Kagome Heisenberg antiferromagnet, because there is no magnetic phase transition down to approximately 50 mK. We investigated its local magnetic and lattice environments with NMR techniques. We demonstrate that the intrinsic local spin susceptibility decreases toward T=0, but that slow freezing of the lattice near approximately 50 K, presumably associated with OH bonds, contributes to a large increase of local spin susceptibility and its distribution. Spin dynamics near T=0 obey a power-law behavior in high magnetic fields. 相似文献
118.
Shahram Pouya Manoochehr M. Koochesfahani Andrew B. Greytak Moungi G. Bawendi Daniel G. Nocera 《Experiments in fluids》2008,44(6):1035-1038
Near-surface velocity measurements are carried out with quantum dot (QD) nanoparticles using evanescent wave illumination.
Relying on the small size of QDs, their correspondingly small hydrodynamic radius and high Brownian diffusion coefficient,
we consider the situation where the tracer diffusion length over the inter-frame time Δt is large compared to the size of the interrogation region next to the wall. While keeping all other experimental parameters
fixed, we systematically increase Δt by as much as a factor of 25, resulting in an increase of the QD diffusion length by a factor of 5. Data indicate a significant
overestimation of the “apparent” mean velocity measured experimentally. These results provide a direct confirmation of the
phenomenon of diffusion-induced bias described by the simulations of Sadr et al. (2007). 相似文献
119.
Dempsey JL Esswein AJ Manke DR Rosenthal J Soper JD Nocera DG 《Inorganic chemistry》2005,44(20):6879-6892
Energy conversion cycles are aimed at driving unfavorable, small-molecule activation reactions with a photon harnessed directly by a transition-metal catalyst or indirectly by a transition-metal catalyst at the surface of a photovoltaic cell. The construction of such cycles confronts daunting challenges because they rely on chemical transformations not understood at the most basic levels. These transformations include multielectron transfer, proton-coupled electron transfer, and bond-breaking and -making reactions of energy-poor substrates. We have begun to explore these poorly understood areas of molecular science with transition-metal complexes that promote hydrogen production and oxygen bond-breaking and -making chemistry of consequence to water splitting. 相似文献
120.
Chang MC Miller SE Carpenter SD Stubbe J Nocera DG 《The Journal of organic chemistry》2002,67(19):6820-6822
We describe a general method for the unimolecular photochemical generation of tyrosyl radicals from a diaryl oxalate ester platform on the nanosecond time scale. Symmetric and asymmetric tyrosine oxalate esters have been prepared in gram quantities. Direct photocleavage of the oxalate linkage by laser flash photolysis affords tyrosyl radicals within 50 ns. This approach provides unnatural caged amino acids that may be incorporated into model and biological systems for the study of proton-coupled electron transfer in enzymatic catalysis. 相似文献