Control on arrangement of AgI clusters incorporated into zeolite LTA

AgI clusters were incorporated into Li, Na, and K-form LTA zeolites with a loading number of four AgI molecules per -cage. The X-ray powder diffraction (XRD) patterns and optical absorption spectra of the samples were obtained. The XRD patterns indicate that the sizes of the clusters and their arrangements depend on the type of alkali-cations. AgI clusters with different sizes, i.e., (AgI)_n and (AgI)_8–n (5n7), are arrayed alternatively in Na-form LTA conforming to the space group of P2₁3. AgI-loaded Li-form LTA also conformed to the space group of P2₁3, although (AgI)_n clusters seem to be distributed disorderly. On the contrary, (AgI)₄ cluster is in each cage in K-form LTA conforming to the space group of or . The optical spectra showed that Li and Na-form LTAs include (AgI)_n (5 n), and that K-form LTA includes (AgI)₄ cluster in each cage.     

CNDO studies of Y-Ba-Cu-O superconductors V. Co/Cu substitution

Electronic properties of [Co _n Cu_3–n O₁₂]^–17 and [Ba₈Co _n Cu_3–n O₁₂]^–1 model clusters (n=0–3) are investigated using CNDO molecular orbital method. Our results well reproduce the trends of experimental data on Cu-O bond lengths and supposed negative charge transfer from central Cu(1)O chains to lateral Cu(2)O₂ planes with increasing Co content.     

The oxidation of fullerene [C70] with various oxidants by ultrasonication

The reaction of C₇₀ by ultrasonication with various oxidants such as 3-chloroperoxy benzoic acid (Fluka 99%), 4-methyl morpholine N-oxide (Aldrich 97%), chromium (VI) oxide (Aldrich 99.9%), and oxone^® monopersulfate compound, at room temperature causes the oxidation of fullerene [C₇₀(O)_n] (n=1–2 or n=1). The FAB-MS, UV–visible, FT-IR spectra, and HPLC analysis confirmed that products of fullerene oxidation are [C₇₀(O)_n] (n=1–2 or n=1).     

Magnetic properties of stable structures of small binary clusters

We have studied the optimum geometries and the magnetic behavior of small binary Fe_nGe_m (n+m≤4) clusters usingab initio spin-polarized density functional calculations. Our results reveal that the optimized clusters present high values in the HOMO–LUMO gap and generally prefer structures with high geometries, the local magnetic moments at Fe atoms present an enhancement with respect to Fe bulk magnetization, whereas the Ge atoms present local magnetic moments whose modulus take significative values. The magnetic coupling between Fe and Ge atoms is mainly antiferromagnetic-like. All the clusters studied here present a charge transference from Fe atoms to Ge atoms.     

Structure,electronic properties and vibrational spectra of (MgF2)n clusters through a combination of genetic algorithm and DFT-based approach

In this article, we look at the option of using a stochastic optimisation technique, namely genetic algorithm (GA) in association with density functional theory (DFT) to find out the global minimum structures of (MgF₂)_n clusters with the range of n being between 2 and 10. To confirm whether the structures are indeed the acceptable ones, we go on to evaluate several properties like IR spectroscopic modes, vertical excitation energy, cluster formation energy, vertical ionisation potential and the HOMO–LUMO gap. We stress on the fact that an initial estimation of structure using GA, on two empirical potentials (with and without inclusion of polarisation), leads to a very quick convergence to structures which are quite close to the structures obtained from quantum chemical calculations done from the outset, such as using a DFT calculation. The general structural trend of these systems to form three-dimensional networks is also clear from our study. The lowest energy isomers of these clusters show preference for four-membered Mg₂F₂ and six-membered Mg₃F₃ rings. In the IR spectra of (MgF₂)_n clusters, a blueshift of the Mg–F symmetric stretch and a redshift of asymmetric Mg–F stretching as n increases are obtained.     

Solvation and chemical reaction of sodium in water clusters

Na_m(H₂O)_n Clusters ( n = 1...200, m = 1...50) are formed in a recently build pick-up arrangement. Preformed water clusters traverse a sodium oven, where sodium atoms are picked up. At low sodium vapour pressure ( < 1×10^-4 mbar) pure Na(H₂O)_n clusters are observed in the mass spectra. At high sodium vapour pressure ( > 1×10^-3 mbar) the water cluster pick up more than 50 Na atoms and reaction products Na(NaOH)_n ( n = 2, 4...50) dominate the mass spectra. The even number of NaOH units in the products indicate that also in a finite cluster the reaction occurs in pairs as in the macroscopic reaction. Received 4 December 2000     

WnNim(n+m=8)团簇的极性和光谱性质的理论研究

采用密度泛函理论(DFT)中的B3LYP方法,在LANL2DZ基组水平上对WnNim(n+m=8)团簇的各种可能构型进行了几何参数全优化,得到了它们的基态构型;并对基态构型的偶极距、极化率、红外光谱和拉曼光谱性质进行了分析,结果表明:团簇WnNim(n+m=8)都具有极性,富W团簇非线性光学效应强,容易被外加场极化;振动频率主要分布在0-350 cm-1范围内,团簇W4Ni4因其振动方式的特殊性,红外光谱和拉曼光谱在频率421.971 cm-1处,都有明显强峰;团簇W5Ni3因其结构的高对称性在振动光谱中出现多处共振现象.     

(OsnN)0,±(n=1-6)团簇电子结构与光谱性质的理论研究

采用密度泛函理论中的杂化密度泛函B3LYP方法在赝势基组LANL2DZ水平上对Os_nN^0,±(n=1-6)团簇的各种可能构型进行了几何结构优化,得出了它们的基态构型,并对基态结构的磁学性质、自然键轨道(NBO)、光谱和芳香性进行了理论研究. 研究结果表明:OsN^-和Os₅N^-团簇发生了"磁矩猝灭"的现象,在Os₂N和Os₄N< 关键词： nN^0,±(n=1-6)团簇')" href="#">Os_nN^0,±(n=1-6)团簇 电子结构 光谱性质 密度泛函理论     

Evolution of the Electroluminescence Spectra and the Acoustic Emission of the Epitaxial Structures of GaAsP

The dependence of the spectral position of the electroluminescence bands of epitaxial light-emitting diode n ⁺–n–p structures (GaAs_0.15P_0.85) on the density of a direct heterojunction current at different successive instants of time — before an acoustic emission and after it — has been revealed. The shifts of the electroluminescence bands accompanied by acoustic emission can be divided into three types according to the density of the current: (1) short-term shifts due to relaxation of the defect structure of a sample — at relatively low currents, (2) the magnitude of the reverse shift being determined by the current density — at large currents, and (3) formation of an IR band (1.5–1.1 eV) with irreversible degradation changing in the red (1.75 eV) and green (2.19 eV) bands of the electroluminescence spectrum — at ultrahigh currents (100–200 A/cm²).     

Mössbauer and infrared studies of the Cu-Cr ferrites

Ferrites of the system CuCr_xFe_2–x O₄, wherex=0,0.2,0.4, 0.6 and 0.8, have been studied by Mössbauer and IR absorption spectra. Mössbauer spectra were recorded at room temperature. The spectra of all samples showed two well defined Zeeman patterns corresponding to A and B sites. The effect of the variation of chromium substitution on the various hyperfine interactions has been discussed. The cationic distribution makes clear that all Cr³⁺ ions occupy octahedral sites. The IR spectra in the range 200–4000 cm^–1 showed the presence of four bands. The high and low frequency bandsv ₁ andv ₂ belong to the tetrahedral and octahedral sites, respectively. Small bandsv ₃ andv ₄are observed around v₂ and are assigned to the octahedral divalent metal-oxygen ion complexes and the lattice vibrations of the system, respectively.     

Gas-phase vibrational spectroscopy and ab initio calculations of Rb(H2O)n and Rb(H2O)nAr cluster ions

The competition between ion–water electrostatic interactions and water–water hydrogen bonding in cluster ions depends on several factors, including charge density of the ion and temperature of the system. Infrared photodissociation spectra of Rb⁺(H₂O)_n=2–5 and Rb⁺(H₂O)_n=1–5Ar are presented here and compared to previous experiments involving potassium and cesium. The temperature, or internal energy, of hydrated rubidium cluster ions is controlled by varying the evaporative path available for cluster formation. Warmer clusters (with effective temperatures of 250–500 K) are formed by the evaporation of water, while colder clusters (40–120 K) can be formed by argon evaporation. Colder cluster ions tend to favor conformers with more hydrogen bonds compared to those cluster ions at warmer temperatures. Previous work from this laboratory has shown significant and dramatic differences between the spectra of hydrated potassium and cesium ions. With a charge density intermediate between that of K⁺ and Cs⁺, Rb⁺ plays an important role in bridging the gap in our previous studies.     

On the “near to minimal” canonical realizations of the lie algebraC n

It is proved that canonical realizations of the Lie algebraC _n in the quotient division ringD _2(2n–2) of the Weyl algebraW _2(22–2) in 2n – 2 quantum canonical pairs are, in a definite sense, related to the standard minimal one inD _2n D _2(2n–2). Further, in any realization ofC _n inW _2(2n-1) all Casimir operators are realized by multiples of identity element.     

Multiple-Photon Dynamics in Molecules: A New Approach to High Resolution Spectroscopy of Highly Excited Vibrational States

Multi-photon transitions with two simultaneously interacting IR laser fields lead to final excited states with frequenciesnν = n₁ν₁+ n₂ν₂, withnthe total number of photons absorbed and (n,n₁,n₂) = (2, 1, 1), (3, 2, 1), (4, 1, 3), etc. The nature of the actual transition is determined by shift measurements, where the lasers are frequency-tuned by δν_iin opposite directions keeping the sum frequency,nν, resonant with the molecular transition. This technique opens a new spectral range for multi-photon transitions and a unique identification of the observed features. Forn₁andn₂both positive the excitation will lead to a “normal” up–up multi-photon transition. Many three- and four-photon transitions in the ν₃vibrational ladder of SF₆could be resolved with a resolution of 1 MHz, as well as four new two-photon transitions. As long asn₁+ n₂≥ 0, one of the twon_imay be negative resulting in an, e.g., up–down excitation pathway with its particular selection rules. The up–down excitations are demonstrated both for one- and two-photon transitions using the frequency shift technique. The different possible excitation schemes which meet the resonance condition for these transitions lead to interference effects and local couplings to highly excited states. Changes in resonance frequency for a one-photon transition (n= 1), due to these effects, are demonstrated. Evidently, the radiative coupling of participating levels to high-lying or quasi-continuum states may drastically change for different δν_ileading both to ac Stark shift and transition probability variations.     

Electronic structure and infrared spectrum of a WnC0＇± （n= 1-6） cluster

W_nC^0,± (n=1-6) clusters are investigated by using the density functional theory (DFT) at the B3LYP/LANL2DZ level. We find that the neutral, anionic and cationic ground state structures are similar within the same size, and constituted by substituting a C atom for one W atom in the structures of W_n+1 clusters. The natural bond orbital (NBO) charge analyses indicate that the direction of electron transfer is from the W atom to the 2p orbital of the C atom. In addition, the calculated infrared spectra of the W_nC^0,± (n=2-6) clusters manifest that the vibrational frequencies of neutral, anionic and cationic clusters are similar in a range of 80 cm^-1-864 cm^-1. The high frequency, strong peak modes are found to be an almost stretched deformation of the carbide atom. Finally, the polarizabilities of W_nC^0,± (n=1-6) clusters are also discussed.     

Time-dependent density functional theory study on electronic excited states of the hydrogen-bonded solute-solvent phenol-(H2O)n (n=3-5) clusters

The solute-solvent interactions of hydrogen-bonded phenol-(H₂O)_n (n=3-5) clusters in electronic excited states were investigated by means of the time-dependent density functional theory (TDDFT) method. The geometric structures and IR spectra in ground state, S₁ state, and T₁ state of the clusters, were calculated using the density functional theory (DFT) and TDDFT methods. Only the ring form isomer, the most stable one of the cluster, was considered in this study. Four, five and six intermolecular hydrogen bonds were formed in phenol-(H₂O)₃, phenol-(H₂O)₄, and phenol-(H₂O)₅ clusters, respectively. Based on the analysis of IR spectra, it is revealed that the “window region” between unshifted and shifted absorption bands in both S₁ and T₁ state becomes broader compared with that in ground state for the corresponding clusters. Furthermore, two interesting phenomenon were observed: (1) with the anticlockwise order of the ring formed by the intermolecular hydrogen bonds in the H-bonded phenol-(H₂O)_n (n=3-5) clusters, the strengths of the intermolecular hydrogen bonds decrease in all the S₀, S₁ and T₁ states; (2) upon electronic excitation, the smaller the distance between phenol and water is, the larger the change of intermolecular hydrogen bonds strength is. Moreover, the intermolecular hydrogen bond (phenolic OH is the H donor) is strengthened in excited state compared with that in ground state. But the intermolecular hydrogen bond (phenolic OH is the H acceptor) is weakened in excited state.     

CNDO studies of Y-Ba-Cu-O superconductors IV. The oxygen content effect

The dependence of the electronic structure of superconducting YBa₂Cu₃O _y , is investigated using a quasi-relativistic CNDO/1 molecular orbital method. Electronic structures of model clusters [Ba₈Cu₃O _n ] ^q with total chargesq=23–2n forn=11 to 14 in various Cu(1) coordination geometries are compared. The increasing oxygen content causes the electron density transfer from the central Cu(1)O(1,5) _x area to the lateral Cu(2)O(3,4)₂ sheets. The isomerization effects are important for the structures withn=12.     

Effect of aerosil dispersions on the nematic-to-isotropic interface

The effect of silica aerosils on the kinetics of the first-order nematic-isotropic (NI) phase transition is phenomenologically described in the framework of the time-dependent Landau-Ginzburg equation. A steady-state solution to the equation is presented such that the NI interface may propagate with a solitary-like wave profile under constant quenching. The results provide a plausible basis for the interpretation of the dynamical effects of quenched disorder in the liquid-crystal systems, caused by randomly interconnected porous media, such as aerosils. In the low silica aerosil ρ_s ( ≤0.1 g/cm^3) regime, the calculated values of the interface velocity v(T,ρ_s), the interface thickness κ(T,ρ_s), and the critical radius of a spherical nucleus of new nematic phase in a bulk isotropic environment, composed of polar molecules, such as 4-n-octyl- 4^′- cyanobiphenyl and 4-n-heptyl- 4^′- cyanobiphenyl shows that the effect of silica aerosils on the kinetics is reflected in a shifting of the set of temperature-dependent curves to lower temperature values.-1     

The structural, optical, and dielectric spectroscopy studies of novel ZnO–As2O3 glass system with Sb2O3 as additive

ZnO–As₂O₃–Sb₂O₃ glasses of varying concentrations of Sb₂O₃ with ZnO (ranging from 5 to 45 mol%) are prepared. A number of studies, including differential thermal analysis, and study of spectroscopic properties (viz., optical absorption and IR spectra) and dielectric properties (constant ε′, loss tan δ and ac conductivity σ_ac) over a wide range of frequency and temperature of these glasses are carried out. Analyses of the results of these investigations have indicated that the glasses containing higher concentrations of Sb₂O₃ are more suitable for non-linear optical (NLO) applications.     

Positron annihilation and Hall effect in electron irradiatedn-InP crystals

Positron annihilation and Hall effect inn-InP crystals as a function of electron irradiation up to 1 · 10¹⁹ cm^–2 and post-irradiated isochronal annealing up to 550 °C have been studied. It is concluded that in irradiatedn-InP samples positrons interact with negatively charged acceptor-type defect with level atE _c –0.33 eV, probablyV _In (primary defect). In post-irradiated isochronal annealed (up to 330 °C) samples ofn-InP positron trapping occurs preferably in secondary defects-vacancy clusters, which are formed in the temperature range (150–300 °C). Inn-InP crystals containing radiation induced defects the trapping rate was found to decrease with temperature in the range (300–77) K.     

Comparative ab initio studies of small tin and lead clusters

We have performed ab initio total-energy pseudopotential calculations on neutral and negatively charged Snn and Pb_n (n = 3 ? 10) clusters. The lowest energy structures have been determined for all clusters, and the stabilities of neutral clusters were investigated by comparing their evaporation energies and stability functions. Clusters with n = 7,10 were found to be most stable while the clusters with n = 8 and Pb_s were much less stable, in agreement with features of the observed mass spectra. Calculations on Sn^?_n and Pb^?_n show that both atomic and electronic structures of a neutral cluster change substantially upon charging. The densities of states of Sn^?_n clusters reproduce the main features of the experimental photoelectron spectra. The agreement is poorer for Pb^?_n clusters where the calculations underestimate the separation between energy levels which we think is due to the larger spin-orbit splitting in Pb, which was neglected in the calculations. We found that the differences between Sn and Pb clusters cannot be completely addressed without a more complete accounting of relativistic effects. The electron affinities of Sn_n and Pb_n clusters have also been calculated and the results agree fairly well with experimental values. Finally we considered Sn^2?₄ and Pb^2?₄ clusters and related the results to the formation of Zintl anions in liquid alkali-Sn and alkali-Pb alloys.