A variable temperature EPR study of Mn(2+)-doped NH(4)Cl(0.9)I(0.1) single crystal at 170 GHz: zero-field splitting parameter and its absolute sign

EPR measurements have been carried out on a single crystal of Mn(2+)-doped NH(4)Cl(0.9)I(0.1) at 170-GHz in the temperature range of 312-4.2K. The spectra have been analyzed (i) to estimate the spin-Hamiltonian parameters; (ii) to study the temperature variation of the zero-field splitting (ZFS) parameter; (iii) to confirm the negative absolute sign of the ZFS parameter unequivocally from the temperature-dependent relative intensities of hyperfine sextets at temperatures below 10K; and (iv) to detect the occurrence of a structural phase transition at 4.35K from the change in the structure of the EPR lines with temperature below 10K.     

Shallow donors in semiconductor nanoparticles: limit of the effective mass approximation

The spatial distribution of the electronic wave function of a shallow, interstitial Li donor in a ZnO semiconductor nanocrystal has been determined in the regime of quantum confinement by using the nuclear spins as probes. Hyperfine interactions as monitored by electron nuclear double resonance spectroscopy quantitatively reveal the transition from semiconductor to molecular properties upon reduction of the size of the nanoparticles.     

Sample preparation of archaeological materials for PIXE analysis

A method to prepare thin samples of archeological materials such as potteries and bones for PIXE analysis is presented. In this method fine powder of the matter under analysis is suspended and deposited on polycarbonate filters. The process takes place in a chamber where clean air and the powder are mixed and forced to pass through the filter. Thin samples with typical mass density of about 50 g cm^–2 are obtained. The uniformity of the mass deposit has been optically tested with a He–Ne laser showing fluctuations of the order of one percent. Samples of clay standards from NIST were prepared with this method and analyzed by PIXE. The agreement between our results and NIST values is very good, with linear correlation factors close to unity. The method was applied to study the elemental composition of clay from different fragments of a Chilean pre-Hispanic pottery piece. These results are very consistent showing that the analysis of samples from a small fragment can represent the whole piece.Work supported in part by FONDECYT Grant 1052-92.     

Start-phase ionization dynamics in the laser plasma at low gas target densities

In Xe laser-produced-plasma sources of short-wave radiation, the laser-energy-to-EUV conversion efficiency (CE) proves substantially less than theoretical expectations. In the present work, a calculated estimate has been made which indicates that a long period of the primary ionization, lasting up to a moment when high-Z ions appear to emit short-wave photons, can be one of main causes for this. During that period the plasma remains low-ionized and absorbs weakly the laser energy. The estimate above has been experimentally confirmed with spectroscopic data and those on the effective ion charge derived from measured absorption of the laser radiation in the plasma. A preionization of the gas target with an ultraviolet (UV) excimer laser pulse is proposed as a method to accelerate the ionization process and consequently, to enhance CE.     

Molecular modeling of the olefin metathesis by tungsten(0) carbene complexes

Density functional and second-order Moller–Plesset theory were used to model W(0) carbene mediated homogeneous metathesis reaction of propylene. The calculations show that the rate determining step of the metathesis is the initiation. After the initiation has been completed the rate determining step becomes dissociation of olefin–metallocarbene complex. The low stereoselectivity of the olefin metathesis reaction is due to the close matching of activation energies for cis and trans isomer formation and the fast cis–trans isomerization caused by the catalysts. The non-productive olefin metathesis reaction always dominates the reaction mixture owing to its very low activation energy. The electronic structure of metal carbene olefin complexes can be described as a combination of donor–acceptor interactions between HOMO of the olefin and LUMO of metal carbene located at carbene carbon on the one hand, and the Dewar, Chatt and Duncanson back donation scheme on the other.     

Quantum information and entanglement transfer for qutrits

We propose a scheme for the transfer of quantum information among distant qutrits. We apply this scheme to the distribution of entanglement of qutrits states among distant nodes and to the generation of multipartite antisymmetric states. We also discuss applications to quantum secret sharing.