Search

Coupled-cluster theory (CCSD(T)) extrapolated to the complete basis set limit was used for examining the thermochemical parameters of trifluoromethanol. Energy barrier of 28.7 kcal/mol was observed in a six-membered ring dimer.

The syntheses, structures, and magnetic properties of the mixed-metal complexes with [[[Ce.sub.4][Mn.sub.10][O.sub.10][(OMe).sub.6]].sup.18+] and [[[Th.sub.6][Mn.sub.10][O.sub.22][(OH).sub.2]].sup.18+] cores are described. The results have represented a caveat against taking the ac signals as sufficient proof of a single-sufficient proof (SMM).

A study of electron localization in dilute solutions of polar molecules in nonplanar liquids is conducted using TA spectroscopy and conductivity. The results suggested that a composite cluster anion consisting of a few polar molecules imbedded in an alkane 'matrix' might be the closet gas-phase analogue to the core of solvated electron in a neat polar liquid.

The postimplantation clustering and transient enhanced diffusion (TED) in boron in profiles with peak concentrations below the boron (B) solubility limit were simulated using the A, m and kd as parameters for the B clustering, four parameters for the self-interstitial cluster and the effective diffusivities of dopants and self-interstitials. Accurate predictions for the B clustering and TED over broad ranges of B concentration, implantation dose, annealing times, energy and temperatures were generated.

The electrical properties of interstitial clusters in ion-implanted silicon (Si) were characterized using deep level transient spectroscopy. The study focused on n-type Si and examined how the kinetics of evolution and dissociation of these clusters are affected by impurity content and implantation dose. The findings showed that only the K lines and the B lines are associated with interstitial clusters. It was found that B1, B2, KA and KS belong to the same defect clusters while KZ is linked to the occurrence of O in the Si.

A pulsed electron-beam high-pressure mass spectrometer was used to evaluate the gas-phase clustering reactions involving fluoride with diatomic molecules O2, N2 and CO, where F-(Sol)n-1 + Sol=F-(Sol)n and Sol represents the three molecules. F-(O2)n exhibited the smallest bond strength for all the cluster ions examined. An electrostatic interaction was observed between F- and O2, while charge transfer occurred for F- complexes with N2 and CO.

Femtosecond pump-probe negative ion-to-neutral-to-positive ion spectroscopy was used in a theoretical analysis of the multistate dynamics of the Ag(sub 3)(super -)/Ag(sub 3)/Ag(sub 3)(super +) system on the time scale of nuclear motion. Configurational relaxation, intracluster collision, and onset of intracluster vibrational relaxation (IVR), resonant and dissipative IVR and vibrational equilibration were found to be involved in the dynamics of the Ag(sub 3) cluster. Theory was revealed as essential for clarifying the abundant dynamic information on geometrical change, completion of IVR, and vibrational coherence effects.

Research was conducted to examine the influence of the implanted K-cluster size distribution on the shift of W work function. Work function shift of up to 2 eV can be attributed to the simple assumption of small K-clusters formation inside the metal surface layer. A revised model, which considers most of the parameters for the implantation process and the alkali-cluster formation inside the surface, is proposed. With the help of previous experimental results, determining the most probable K-cluster size distribution becomes possible.

The gas-phase clustering of water, methanol and acetonitrile with the potassium ion are studied using ab initio calculations. Results show that the RHF/DZP//RHF/DZP calculations are in good agreement with MP2/6-31+G*//RHF/6-31+G* calculations and experimental data for n values of up to four or five. The increase in binding energy with n is also almost linear for all solvents while the relative binding strength for small clusters up to n=3 follows the order acetonitrile > water > methanol.

A novel method of synthesizing homoleptic neopentide Re3(mu-OCH2CMe3)3(OCH2CMe3)6 and hydrido-neopentide trirhenium(III) clusters was designed. Re3(mu-OCH2CMe3)3(OCH2-CMe3)3 was synthesized when Re3(mu-Cl)3Cl6(THF)3 was made to react with NaOCH2CMe3. Spectroscopic and X-ray crystallographic data were utilized to reveal that the terminal cis-alkoxide ligands at the unique rhenium atom binds with [Na(THF)2]+.

The process of yielding a tetrameric [{Cu(OC6H3Ph2)(CO)]2] dimer from carbonylation of 2,6-dphenylphenoxocopper(I), tetrameric [(CuOC6H3Ph2)4] was described. The parent compound, aryl oxide, resulted to a mu2-phenoxo bridged dimer comprising of a three-coordinated copper(I) with longer copper-oxide bonds. It was indicated that the Cu-C bond was classified to have a sigma character.

Synthesis of highly crystalline nanometer-sized clusters (nanoclusters) of the hexagonal (2H polytype) molybdenum sulfide (MoS2) layered compound showed highly structured, bandlike optical absorption and photoluminescence spectra for the nanoclusters. The clusters' optical properties are conditioned by strong quantum confinement effects. Confinement magnitude is affected by dimensionality.

The structure and electrochemistry of Ni3(micro3-CNCH3)(micro3-I)(micro2-dppm)3 was synthesized with its precursor, Ni3(micro3-CNCH3)(micro3-I)(micro2-dppm)2(CNCH3)2 yielded triangular nickel clusters that can be used as electrocatalysts for carbon dioxide reduction. Both clusters displayed applications in CO2 reduction and also in photochemical generation of CO2- radical anion.

(H2O)2Cl- and (H2O)3Cl- dissociation kinetics at almost zero pressure via absorption of infrared photons from the background radiation field have been compared with theoretical predictions and kinetic modeling. Results showed that observed rates and temperature dependences are quantitatively predictable from molecular characteristics derived from quantum chemistry.

The term 'clusters' is usually used to describe aggregates of atoms that are to large to be referred to as molecules and too small to resemble small pieces of crystal. These aggregates generally do not have the same structure or atomic arrangement as a bulk solid and can change structure with the addition of just one or a few atoms. As the number of atoms increases, eventually a crystal-like structure is established, and the addition of new atoms does not change the bul structure. A motivation for studying clusters is the desire to understand how physical properties evolve in the transition from atom to molecule to cluster t small particle to solid. At present one has a good understanding of the end points of such an evolution, but has still a poor knowledge of the intermediate situations. In particular, while one understands reasonably well why a sodium atom is yellow and why this colour essentially is absent in the electromagnetic spectrum of bulk sodium, we still do not have an accurate theory which explains the spectrum of colours displayed by small sodium clusters. Much progress towards this goal can be achieved by making use of well-established results in nuclear physics. It turns out that there is a close analogy between metal clusters and atomic nuclei, and knowledge acquired during the past 40 years in the study of the response of nuclei to photons helps with the understanding of the absorption of light by microcrystals. The main result of developing such an analogy seems to be that the properties of finite, many-particle systems do not depend so much on the nature of the particles forming the system or the forces acting among them, but on the fact that they move in a confined volume and that they are many of them.

A novel nonanuclear cluster, (PPh4)(((C5Me5)WS3Cu2)3S2), was generated from the reaction of (PPh4)2(Cp*WS3Cu3Br3)2 and Li2S2 in CH3CN. Data from the X-ray analysis of the cluster reveal that the three WS3Cu2 clusters were interconnected by two mu3-S atoms. The isolation of the unusual nonanuclear cluster demonstrates the convenience of using Li2S2 or related sulfur compounds to aggregate preformed clusters.

The completely renormalized coupled-cluster (CR-CC) method with singles, doubles and noniterative triples are used for studying the open-shell system. The activation energies of the [C.sub.2][H.sub.4] + H -> [C.sub.2][H.sub.5] forward and reverse reactions and the triplet states of the C[H.sub.2] and [H.sub.2][Si.sub.2][O.sub,2] biradicals are used for indicating that the dependence of the restricted open-shell Hartree-Fock (ROHF)-based CR-CC energies on the method of canonicalization of the ROHF orbitals is negligible.

Gauge-origin-independent calculations of the Faraday B term of magnetic circular dichroism (MCD) are described for a series of conjugated cluster singles and double (CCSD) model and London orbitals. The parallel displacement of the spectra is attributed to the shift in the excitation energies due to correlation beyond CCSD, as observed when comparing vertical CCSD and CC3 equilibrium-geometry excitation energies.

The article describes the benchmark, near basis set limit fc-CCSD(T) equilibrium harmonic frequencies for a set of 12 closed-shell and five open-shell molecules, which is computed numerically by using the CCSD(T)-R12 method. The corrections due to core-valance correlation are used for assessing the accuracy of the benchmark data, along with corrections from scalar relativistic effects.

The process of photoreversible multiple additions of hydrogen to a highly unsaturated platinum-rhenium cluster complex is described. The highly unsaturated compound [Pt.sub.3][Re.sub.2][(CO).sub.6][(P[Bu.sub.3.sup.t].sub.3], sequentially adds 3 equiv of hydrogen at room temperature in a process that can be reversed partially by application of UV-vis irradiation.

Quantum cluster theories, a set of approximation for infinite lattice models that treat correlations within the cluster explicitly and correlations at longer length scales either perturbatively or within a mean-field approximation are studied. The three cluster formation, the cluster perturbation theory, the dynamical cluster approximation and the cellular dynamical mean-field theory, are derived and their advantages are compared to common models of correlated electron systems.

The broad, intense peak found near 29kDa in the laser-desorption mass-spectral abundances of various aurothiol (Au:SR) cluster compounds is used to optimize the preferential formation of the species in that mass range. The 29kDa cluster compound is suggested as a cleanly obtained nanocrystal-monolayer assembly that can fulfill the high expectations held for this class of compounds.

Why certain molecules are more stable than others is not always easy to understand, not least because nature's diversity does not permit a unified answer for all classes of compounds. [...]

The postimplantation clustering and transient enhanced diffusion (TED) in boron in profiles with peak concentrations below the boron (B) solubility limit were simulated using the A, m and kd as parameters for the B clustering, four parameters for the self-interstitial cluster and the effective diffusivities of dopants and self-interstitials. Accurate predictions for the B clustering and TED over broad ranges of B concentration, implantation dose, annealing times, energy and temperatures were generated.

The electrical properties of interstitial clusters in ion-implanted silicon (Si) were characterized using deep level transient spectroscopy. The study focused on n-type Si and examined how the kinetics of evolution and dissociation of these clusters are affected by impurity content and implantation dose. The findings showed that only the K lines and the B lines are associated with interstitial clusters. It was found that B1, B2, KA and KS belong to the same defect clusters while KZ is linked to the occurrence of O in the Si.

Research is presented describing the use of water and sodium clusters to determine chemical and microsolvation reactivity.

We present experimental results to illustrate the percolation model, and use this model to describe the structure and mass distribution of clusters, the increase of the connectivity as the percolation threshold is approached, as well as transport properties of electrical percolating networks. We discuss results obtained from neutron and light scattering and from mechanical measurements. A good agreement between theory and experiment allows the growth of polymer clusters during the gelation process to be understood. Results obtained from mechanical measurements are quite similar to the behaviour of electrical properties of percolating networks, but are not yet understood completely.

Covalent Group IV Atomic Clusters SCIENTIFIC INVESTIGATIONS OF THE PROPERTIES OF CLUSTERSof atoms have expanded rapidly in the last 5 years. The goal in many of these studies is to [...]

A novel type of medium-dependent reversible cluster that includes the A33C form of Pyrococcus furiosus ferredoxin (PfFd) was discovered. The A33C PfFd was prepared and characterized to evaluate the effects of the location of additional free cysteine adjacent to the cluster. The resonance, which was found to be 1.0 +- 0.1 spins/molecule, was similar to that caused by ferricyanide oxidation of wild-type PfFd, thereby pointing to the existence of one {Fe3S4}+ cluster per molecule.

A study was conducted to examine the growth of cationic silicon clusters in a remote silane plasma. Using ion mass spectrometry and Langmuir probe measurements. it was revealed that the formation of cationic clusters is induced by sequential ion-molecule clustering reactions and not by direct ionization of polysilanes. It was also noted that low electron density triggers the growth of larger cationic clusters.

Another fusion dream is hanging by a thread. In September 1989, a research trio at Brookhaven National Laboratory (BNL) reported what looked to them like a promising new route to [...]