Chemical Physics Letters (v.388, #4-6)

The recombination of the geminate radical pairs in parallel combined magnetic fields by O.A. Ponomarev; S.I. Kubarev; I.S. Kubareva; I.P. Susak; A.S. Shigaev (231-235).
The recombination probability of the model radical pair was demonstrated to have properties to depend resonantly and non-monotonously on the constant magnetic field amplitude and also on the variable magnetic field amplitude and frequency in the event that the fields were in parallel. It has been noted that the similar resonance and multipeak responses arised under changes of frequency and amplitude of magnetic fields in many biological experiments. It has been proposed that the control mechanisms of the magnetic fields at the molecular level which had been opened up previously, may be essential to magnetobiology.

The effect of substitution and isomeric imperfection on the photophysical behaviour of p-phenylenevinylene trimers by J. Seixas de Melo; J. Pina; H.D. Burrows; S. Brocke; O. Herzog; E. Thorn-Csányi (236-241).
Spectroscopic and photophysical properties of two p-phenylenevinylene (PV) trimers, 2,5-substituted diheptyl-(p-phenylenevinylene) and di-[(2-ethylhexyl)oxy]-(p-phenylenevinylene), were studied using absorption spectroscopy, fluorescence and laser flash photolysis. The change from alkyl to alkyloxy groups red-shifts the absorption and fluorescence bands. The rate of internal conversion is independent of the substitution, whereas alkyloxy substitution increases the S1   ⇝  T1 intersystem crossing rate by an order of magnitude. The relevance for the behaviour of conjugated PPV polymers is discussed. For diheptyl-PV, a sample having ca. 3% of the cis-configuration was also studied. Comparison between the all-trans and the cis-contaminated samples revealed no significant differences in their photophysical properties.

CF3ONO2 yield in the gas phase reaction of CF3O2 radicals with NO by Satoshi Nishida; Kenshi Takahashi; Yutaka Matsumi; Malisa Chiappero; Gustavo Argüello; Timothy J Wallington; Michael D Hurley; James C Ball (242-247).
FTIR smog chamber techniques have been used to show that reaction of CF3O2 radicals with NO proceeds via two channels giving either CF3O + NO2 (5a) or CF3ONO2 (5b) as products. In 700 Torr of N2/O2 diluent at 296 K the branching ratio for CF3 ONO2 formation is k 5b/(k 5a+k 5b)=(1.67±0.27)×10−2. The CF3ONO2 forming channel is in the fall off regime at pressures of 50 Torr and below, while for pressures above 100 Torr the reaction approaches the high-pressure limit. This behavior is consistent with the predictions of recent master equation calculations [Chem. Rev. 103 (2003) 4577].

Using a sophisticated full relativistic all-electron density functional method we are able to describe the correct magnetic ground states of three organic molecules which are chosen as first examples to proof the quality of the method. S=0 for 3,4-dimethyl-tetrahydrofuran and 3,4-dimethyl-tetrahydrothiophene biradicals and S=1 for 1,1,3,4-tetramethyl-cyclopentane biradical. In addition we are able to give a magnetic density distribution within the molecules.

We demonstrate a dramatic enhancement of the cathodic photocurrent of a photoelectrochemical (PEC) device based on the Langmuir–Blodgett (LB) film of poly(3-hexylthiophene) (P3HT) by doping with Dy@C82, which is attributed to the facile photoinduced electron transfer between P3HT and Dy@C82. The photocurrent efficiency of the P3HT/Dy@C82 PEC device is found to be composition dependent, which is the highest when the molar ratio of P3HT:Dy@C82 is 20:1. The optimal PEC performance is strongly correlated with the ordered molecular arrangements. A possible mechanism for the cathodic photocurrent generation is proposed and supported by the studies on the bilayer PEC device.

In situ technique of thermal analysis–mass spectroscopy coupling was employed to investigate the growth of carbon nanotubes (CNTs) by means of chemical vapor deposition of benzene at the temperature of 700 °C. It was found that the building blocks of CNTs depended on the coverage of benzene over the catalyst. As soon as the molecules of benzene were introduced onto the catalyst at high temperature, a fraction of small hydrocarbon fragments were generated and these fragments likely participate in the construction of CNTs. As the catalyst was heavily covered at room temperature, there is no hydrocarbon fragments detected, which led to the growth of CNTs in the six-membered-ring-based model as we early suggested.

We report results of single molecule study of phosphorescent organometallic complex, tris(2-phenylpyridine)-iridium (Ir(ppy)3). Single molecule emission intensities show a wide multi-component distribution. Photobleaching times of molecules emitting with particular intensity are exponentially distributed. The dependence of the inverse of the mean photobleaching time on the emission intensity reveals linear dependence for lower intensities and more complex behavior for higher intensities. The results obtained on Ir(ppy)3 are compared with those of a fluorescent label, diethyloxacarbocyanine.

Dephasing of vibrationally excited molecules at surfaces: CO/Ru(0 0 1) by Mischa Bonn; Christian Hess; Wim G Roeterdink; Hiromu Ueba; Martin Wolf (269-273).
The v=0→1 fundamental and the v=1→2 hot-band transitions of the C–O stretch vibration of CO chemisorbed on Ru(0 0 1) are investigated as a function of temperature using broadband-IR sum-frequency generation spectroscopy. Although the linewidths are markedly different for the two transitions, we demonstrate that the temperature-dependent contribution to the linewidths from anharmonic coupling to the low-frequency frustrated translation mode (giving rise to pure dephasing) is identical for both transitions. This implies that the anharmonic coupling between the high-frequency and the low-frequency mode is independent of the degree of vibrational excitation.

Using DFT computations (B3LYP and BHandHLYP functionals) with isodesmic reactions as working chemical reactions, and extended basis sets with diffuse functions, the standard enthalpies of formation of an α-tocopherol model (where the aliphatic chain and the neighbour methyl group have been changed to hydrogen atoms) and its free radical α-tocopheroxy were theoretically estimated for the first time: −79.4 ± 2.0, and −54.9 ± 2.0 kcal mol−1, respectively. These enthalpies of formation correspond to the O–H bond dissociation enthalpy of BDE(O–H)=76.6 ± 2.0 kcal mol−1, in excellent agreement with the gas-phase experimental value for natural α-tocopherol, which lends confidence to the method and model used.

We present harmonic and anharmonic frequencies of uracil and 2-thiouracil computed using the BLYP and B3LYP density functionals and medium size basis sets. Anharmonic corrections have been obtained by a second order perturbative treatment (PT2) recently introduced by one of the authors in the Gaussian program. At the B3LYP level inclusion of anharmonic contributions reduces the absolute average error by nearly an order of magnitude, whereas BLYP results are not equally satisfactory due to an overall underestimation of harmonic frequencies. The agreement of B3LYP/PT2 results with experiments paves the route for reliable yet affordable studies of molecules of biological interest by a completely automatic procedure without any scaling factor.

Geometries of the ScC2, ScC3 molecules and their anions have been optimised at the CASSCF level. For the first time a cyclic structure is predicted as the ground state for ScC2 . Ab initio adiabatic electron affinities have been obtained by performing single point CASPT2 calculations. The resulting adiabatic electron affinities are in good correspondence with experimental data. The ground states of the two neutral clusters result from a transfer of two metal valence electrons to the ligands. The additional electron of the corresponding anionic clusters occupies a non-bonding sp-hybrid metal orbital.

An ab initio multiconfigurational CASSCF/CASPT2 approach has been used to calculate the electronic structure of the equilibrium conformations of the FeC2, FeC3 complexes and their anions. We have found cyclic C2v structures as the ground states for these clusters, except for the FeC3 cluster for which a C∞v linear structure is predicted. Formally the electronic structure of the FeC n (n=2,3) clusters can be considered as Fe2+C n 2−. The computed adiabatic electron affinities correspond well with the photoelectron spectroscopic data.

Optical-IR double resonance spectrum of the a3A2 triplet levels coupled by intramolecular interactions to the rotational levels of the A1A2 singlet state was measured for H2CS excited to a single rotational level of the vibrationless state. The spectrum was recorded for the J =4, K a=1, K c=3 (413) level. The IR field influence on the fluorescence decay of H2CS excited to the level discussed was also investigated. Theoretical model was used to interpret the results obtained.

Quantum interference effect (QIE) in rotational energy transfer within CO ( A 1 Π, v=0/e 3 Σ , v=1) mixed states in collision with HCl are observed with the interference phase angle θ ST of 101 and 110° for ΔJ=±1 transition, respectively, from the initial J=12 and 13 states. In comparison with the previous similar experiments with He et al. as collision partner, which all give a θ ST<90°, the interference for a same CO transition in collision with HCl changes from constructive to destructive or the reverse since cos  θ ST becomes negative. The bigger θ ST may be explained by the long-range dipole–dipole interaction of proportional to R −3. The physical significance of θ ST is discussed in some details.

Conventional sputter deposition techniques produce alternating layers only when multiple sputtering targets are employed. However, we have demonstrated that the use of only one single sputtering gun in a conventional sputter deposition process could lead to the formation of alternating layers through self-assembling. The periodicities of the layered structure range from 100 to 101 nm. The appearance of alternating nano-scaled layers and the periodicity depend on the type of the target materials and the deposition conditions. Based on the consideration of the deposition rate and the catalytic reaction of metal, the formation such self-assembled alternating nano-scaled layers is explained.

Ectoine is one of the most common compatible solutes found in halophilic bacteria, and has an effect to introduce a tolerance to high salt concentration or high temperature. By analyzing 1 ns molecular dynamics simulations at 370 K, we have shown that, in the ectoine aqueous solution, the water diffusion slows down around a protein (chymotrypsin inhibitor 2 (CI2)), keeping the protein hydration structure essentially unchanged. It is concluded that the slowdown of water diffusion around the backbone amide protons must be one of the decisive factors in reducing the exchange rate of the backbone amide protons, whose reduction is experimentally believed closely related to the tolerance effect.

In a recent Letter, we have shown how a thermodynamic-like theory can be developed starting from the periodic production of certain proteins in the cell cycle [Chem. Phys. Lett. 377 (2003) 627]. The kinetic equations for two protein complexes regulating the cell cycle were assumed to be in Hamiltonian form. This implies that the underlying system is conservative, a hypothesis which is by no means verified by biological systems. The only justification we had for such a choice was the necessity to keep the derivation as simple as possible, so that the essence of the methodology and its development were not shadowed by complicated mathematics. In this short communication, we revisit the theory presented and we generalise it to the case when the system is dissipative. We also show that the theory still holds when the system is not at equilibrium.

Two novel two-photon polymerization initiators with extensive application prospects by Yupeng Tian; Mingliang Zhang; Xiaoqiang Yu; Guibao Xu; Yan Ren; Jiaxiang Yang; Jieying Wu; Xuanjun Zhang; Xutang Tao; Shengyi Zhang; Minhua Jiang (325-329).
Two novel two-photon polymerization initiators, 10-ethyl-3-E-(4-(N,N -di-n-butylamino)styryl)phenothiazine 5 and 10-ethyl-3,7-E,E-bis(4-(N,N -di-n-butyl amino)styryl)phenothiazine 6, have been efficiently synthesized with room temperature solid phase Wittig reaction. Two initiators were found to exhibit good single-photon fluorescence emission and their quantum yields, lifetimes and solvent effects have been studied in detail. Two-photon fluorescence spectra were investigated under 800 nm fs laser pulse and two-photon absorption (TPA) cross-sections of the initiators have been evaluated by theoretical calculation.Two-photon initiating polymerization microfabrication experiments have been carried out and artificial defects were made and polymerization mechanism was also discussed.

With the tight-binding model of semiconductor carbon nanotubes, the third-order nonlinearity of carbon nanotubes has been studied theoretically by using the two-band approximation. Taking the contribution of pure interband transition of π-electron and combined intraband–interband motion into account, a spectrum of χ THG (3) has been obtained. The results show that for a typical semiconductor carbon nanotube the off-resonant magnitude of |χ THG (3)| reaches 10−7–10−8 esu and |χ THG (3)| value at three-photon resonant peak 10−5 esu. The nonlinear susceptibility χ THG (3) strongly depends on the nanotubes geometry and considerably increases with the increasing radii of carbon nanotubes. In addition, it is found that the third-order nonlinear susceptibility of carbon nanotubes obeys 1/Δ g 6 law.

Effective mass Schrödinger equation of an artificial atom in two dimensions with anharmonicity in confinement potential is solved by linear variational method using an appropriate harmonic oscillator basis set. Linear response to electric field is computed and correlated with changes in the electronic probability density distribution.

The M(H2O)19–21 + clusters (M = Na or K in cavity) consisting of broken and distorted dodecahedral cages are studied by optimizing geometry at the B3LYP/6-311++G** level. The stabilization energy (relative to separated H2O and M+) per monomer (SEP) exhibits a maximum for K(H2O)20 + and no such maximum for Na(H2O)20 + cluster. While K in dodecahedral cavity carries a +1 charge, Na remains as a neutral atom, and suggests that the electron affinity (EA) of Na+  > EA of (H2O)20 + dodecahedral cage > EA of K+. On the basis of above trends in the SEP values and the charge on the metal, one can explain the absence of a magic number peak for Na(H2O)20 + and the presence of the magic peak for K(H2O)20 + cluster.

Traditionally, only the maximally compact ground states are considered in the designability studies of the lattice proteins. We consider the consequences of inclusion of all clustered conformations as an extended set of the ground states. We calculated designabilities and performed folding simulations for 12-mers using traditional and extended ground state definitions. We show that the choice of compact conformations as the ground states may produce severe artifacts in designability and folding kinetics studies, even for such small model systems. The physically realistic concept of the clustered ground states allows to overcome these difficulties.

The dipole polarizability, static first hyperpolarizability and UV–Vis spectrum of the recently identified nano-sized tetrahedral cluster of Au20 have been investigated by using time-dependent density functional response theory. We have discovered that the Au20 cluster possesses remarkably large molecular second-order optical nonlinearity with the first hyperpolarizabilty (β xyz ) calculated to be 14.3 × 10−30 esu. The analysis of the low-energy absorption band suggests that the charge transfer from the edged gold atoms to the vertex ones plays the key role in nonlinear optical (NLO) response of Au20.

Two-color polarization spectroscopy was used to investigate rotational energy transfer (RET) and relaxation of orientation and alignment in the ground electronic state of OH in an atmospheric-pressure methane–air flame. Two independently tunable lasers produced nearly transform-limited infrared and ultraviolet pulses of 50 ps duration. The infrared laser excited rovibrational transitions, and delayed ultraviolet pulses probed electronic transitions from either the directly pumped or collisionally populated states. Alignment and orientation relaxation times were measured for individual rotational levels in OH X 2 Π 3/2(v=1), and the feasibility of time-domain investigation of state-to-state energy transfer processes was demonstrated.

Density functional theory study of proton hopping in MCM-22 zeolite by Yan Wang; Danhong Zhou; Gang Yang; Xianchun Liu; Ding Ma; DongBa Liang; Xinhe Bao (363-366).
Proton hopping between O-sites among different sites of the MCM-22 zeolite has been studied and compared for the first time by density functional theory. According to the results of calculation, it is found that both low and high hopping barriers (ranging from 4.96 to 28.82 kcal/mol) exist in the supercage as well as the sinusoidal channel systems, and there is no correlation between the proton transfer activation energy and proton affinity of the donor oxygen. The calculation also shows that other factors, the channel system and the geometric parameters of the equilibrium state, affect the hopping barriers of different sites.

The absorption and resonance Raman excitation profiles of ν 4=1389 and ν 5=1195 cm−1 fundamentals are studied in the excitation region corresponding to the 12 B 2g →12 B 3u transition in the tetracyanoquinodimethane (TCNQ) monoanion. Both Franck–Condon (FC) and mode-mixing (Dushinsky) effects in the 12 B 3u electronic state are considered. These effects are discussed in terms of B3LYP and CASSCF methods. It is shown that both absorption and excitation profiles discussed in the 12 B 2g →12 B 3u excitation region are in excellent agreement with those available from the experiment. The computations confirm D2h symmetry of the TCNQ molecule in its lowest energy 12 B 3u doublet. On the other hand in at least one of two states 22 B 3u or 12 A u , the computations suggest that the symmetry of TCNQ monoanion is unstable being reduced from the D2h to the C2h symmetry.

Electronic structure of Mn2O: ferromagnetic spin coupling stabilized by oxidation by Kensuke Tono; Akira Terasaki; Toshiaki Ohta; Tamotsu Kondow (374-378).
The electronic structure of Mn2O was investigated by photoelectron spectroscopy and the density-functional theory (DFT). The cluster anion was found to possess a spin magnetic moment as large as 11 μ B (Bohr magneton) due to ferromagnetic coupling between the spins localized on each manganese site. The ferromagnetic state gains substantial stability via superexchange-type interaction through an oxygen atom at the bridge site. This mechanism is manifested in its electronic structure, which exhibits significant hybridization among the Mn 3d, Mn 4s, and O 2p orbitals.

Magnetic specific heat of the low-temperature phase of rubidium manganese hexacyanoferrate by Hiroko Tokoro; Shin-ichi Ohkoshi; Tomoyuki Matsuda; Toshiya Hozumi; Kazuhito Hashimoto (379-383).
In the specific heat measurement of RbIMnIII[FeII(CN)6] (MnIII; S=2, FeII; S=0), an anomalous peak due to a long-range magnetic ordering was observed at 11.0 K (T p). The magnetic transition entropy (ΔS mag) and enthalpy (ΔH mag) were evaluated from the magnetic specific heat (C mag) to be 11.8 ± 0.9 J K−1  mol−1 and 125 ± 9 J mol−1, respectively. A detailed analysis of C mag, ΔS mag, ΔH mag, and T p has shown that the present magnetic phase is a three-dimensional Heisenberg-type ferromagnetic lattice of MnIII sites with an exchange coupling constant of ≈+0.5 cm−1. The ferromagnetic ordering is ascribed to the valence delocalization mechanism.

Low-energy electron-stimulated chemical reactions of CO in water ice by S. Yamamoto; A. Beniya; K. Mukai; Y. Yamashita; J. Yoshinobu (384-388).
We investigated low-energy electron-stimulated chemical reactions between CO and water molecules in low-temperature ice using infrared reflection absorption spectroscopy. Carbon dioxide, the formyl radical, formaldehyde, and methanol were produced by electron irradiation of the water/CO/water layered ice. The electron energy threshold and temperature dependence for the chemical reactions were investigated to elucidate the reaction mechanisms.

Adiabatic potential surfaces of the lowest two triplet states and the lowest five quintet states of FeH2 were calculated using ab initio multi-reference singly and doubly excited configuration interaction plus Davidson's type correction. Multi-reference coupled pair approximation was applied to obtain more accurate term energies of the triplet states. In contrast to the quintet states, which are known to be linear, the lowest two triplet states are strongly bent. Vibrational analyses of both quintet and triplet states were carried out. We discuss the effect of non-adiabatic coupling on the bending vibrational levels of 5 B 2 and (2) 5 A 1 through a conical intersection.

Ag(I) ion in liquid ammonia by Ria Armunanto; Christian F Schwenk; Bernhard R Randolf; Bernd M Rode (395-399).
Structural and dynamical properties of Ag+ in liquid ammonia have been evaluated on the basis of a molecular dynamics (MD) simulation by the ab initio quantum mechanical/molecular mechanical (QM/MM) method. The most important region, the first solvation shell, was treated by ab initio quantum mechanics at RHF (Restricted Hartree–Fock) level using double-ζ plus polarization basis sets for Ag+ and ammonia, respectively. For the remaining region in the system newly constructed three-body corrected potential functions were used. The first solvation shell shows a tetrahedral structure with an Ag–N distance of 2.54 Å, with no ammonia exchange process observable within a simulation time of 16 ps. The mean residence time (MRT) of ammonia molecules in the second solvation shell was determined as 12.7 ps. A force constant of 26 N m−1 was observed for the ion–ligand stretching frequency, indicating a more the stable solvate complex than for Ag+ in water.

Laser selective spectroscopy of europium complex embedded in colloidal silica spheres by Dan Zhao; Weiping Qin; Changfeng Wu; Guanshi Qin; Jisen Zhang; Shaozhe Lü (400-405).
Monodisperse colloidal silica spheres embedded with Eu(DBM)3phen complex were synthesized by a modified Stöber method. The europium complex dispersed in the hybrid spheres display the characteristic luminescence of the Eu3+ ions. Low-temperature laser selective spectroscopy and decay dynamics were performed to study the luminescence properties of the pure europium complex and the hybrid spheres. Our results indicate that the method of incorporating the Eu complex into the SiO2 spheres may have a great potential to reduce the contribution of non-radiative processes and optimize the luminescence quantum yield of lanthanide complexes.

Microstructure and magnetic properties of bamboo-like CoPt/Pt multilayered nanowire arrays by Yi-Kun Su; Dong-Huan Qin; Hao-Li Zhang; Hua Li; Hu-Lin Li (406-410).
Highly ordered CoPt/Pt multilayered nanowire arrays have been fabricated successfully by double-pulse electro-deposition into the pores of a porous anodic aluminum oxide (AAO) template. It was found that the nanowires had a bamboo-like structure, in which the section lengths were readily adjusted by varying the pulse width and pulse intensity. XRD and EDX pattern indicated that Pt and disordered fcc CoPt structure were formed during electro-deposition. An in plane anisotropy was found in the samples and high coercivity (Hc=1.8 kOe), squareness (Mr/Ms) around 0.35 was obtained in the samples when the field applied perpendicular to wire axis of CoPt/Pt multilayers, the value of which was much higher than that of pure Co nanowires with the same dimension. The high coercivity obtained in the samples can be attributed to the forming disordered fcc CoPt structure during the deposition of Co.

Hydrothermal synthesis of nanocrystalline and mesoporous titania from aqueous complex titanyl oxalate acid solutions by Yury V Kolen'ko; Victor D Maximov; Alexei V Garshev; Pavel E Meskin; Nikolai N Oleynikov; Bulat R Churagulov (411-415).
Nanocrystalline powders of anatase and rutile type of titania with different morphology and particle size 13–50 nm (XRD) were prepared by a hydrothermal treatment of complex titanyl oxalate acid H2TiO(C2O4)2 (0.28 and 0.07 M) aqueous solutions. The influences of hydrothermal treatment conditions on the formation features, phase composition, particle size, morphology and properties of the products were investigated and discussed. Under the conditions of high temperature hydrolysis of 0.28 M H2TiO(C2O4)2 aqueous solution, the formation of mesoporous anatase particles (60–100 nm, TEM) containing non-intersecting (7–27 nm, TEM) pores with encapsulated solution was observed while hydrothermal treatment of 0.07 M aqueous solutions did not lead to the formation of mesoporous TiO2. The formation mechanism of mesoporous anatase particles was suggested considering the process as recrystallization primary grains aggregates.

Growth of silver nanoclusters embedded in soda glass matrix by P Gangopadhyay; P Magudapathy; R Kesavamoorthy; B.K Panigrahi; K.G.M Nair; P.V Satyam (416-421).
Temperature-controlled-growth of silver nanoclusters in soda glass matrix is investigated by low-frequency Raman scattering spectroscopy. Growth of the nanoclusters is ascribed to the diffusion-controlled precipitation of silver atoms due to annealing the silver-exchanged soda glass samples. For the first time, Rutherford backscattering measurements performed in this system to find out activation energy for the diffusion of silver ions in the glass matrix. Activation energy for the diffusion of silver ions in the glass matrix estimated from different experimental results is found to be consistent.

Using HF and DFT-B3LYP methods, basis set dependence on the optimal geometry of tris(o-phenylenedioxy)cyclotriphosphazene has been investigated. It was found that polarized functions are necessary for an appropriate description of geometry characteristics and electronic structure of this compound. B3LYP/6-31G(d) optimized geometry was found to agree well with crystal data. The study of the electronic structure of the neutral molecule has shown that the frontier orbitals are strongly localized on the three spirocyclic side groups, while injection effect of charge on the structure of the molecule has small structural changes on it, implying a certain stability of the molecular structure.

Current–voltage curves for molecular junctions: the effect of Cl substituents and basis set composition by Charles W. Bauschlicher; John W. Lawson; Alessandra Ricca; Yongqiang Xue; Mark A. Ratner (427-429).
Current–voltage characteristics of gold-benzene-1,4-dithiol-gold junctions are calculated using a combined density functional theory/non-equilibrium Green's functions approach with local atomic basis sets. Improving the basis set with the addition of polarization or diffuse functions has some effect on the computed IV curves, but even the small valence double zeta sets yield reasonable results. The results obtained using the hybrid B3LYP functional give slightly smaller conductance than those obtained using the pure BPW91 approach. Substituting Cl for H on the bridging molecule has only a small effect on the IV curves.

Raman scattering of complex sodium aluminum hydride for hydrogen storage by Daniel J Ross; Mathew D Halls; Abbas G Nazri; Ricardo F Aroca (430-435).
Complex hydride materials are currently under investigation for potential use in hydrogen storage applications. In this report, the Raman spectra of sodium aluminum hydride (NaAlH4) were collected using an excitation laser line at 633 nm. The interpretation and assignment of the observed spectrum of NaAlH4 was aided by cluster-based density functional calculations, using hybrid density functional theory [B3LYP/6-31+G(d,p)], enabling the reliable interpretation of characteristic Raman bands. The assignment and identification of internal vibrational, torsional, and lattice vibrational modes are discussed, providing spectroscopic probes for future physicochemical studies following structural and systemic evolution during the hydriding/dehydriding processes of NaAlH4.

Coagulation of linear carbon molecules into nanoparticles: a molecular dynamics study by Yasutaka Yamaguchi; Tomonari Wakabayashi (436-440).
Using molecular dynamics (MD) simulations, the coagulation of carbon chain molecules that occurs on the subliming surface of a carbon-containing rare-gas matrix is investigated. Intermolecular connections with dangling bonds enhance the sublimation of the matrix and that results in the emission of a layer of nested carbon chains into vacuum at a velocity about 100 m/s. The following conversion from carbon sp- to more stable sp2-type bonds heats up the carbon material above 3000 K. During this process, the nested carbon layer self-anneals via a graphitic mono-layer into a conjunct array of particles with a dimension about 10 nm.

Signal enhancement of NMR spectra of half-integer quadrupolar nuclei in solids using hyperbolic secant pulses by Renée Siegel; Thomas T. Nakashima; Roderick E. Wasylishen (441-445).
Signal enhancement of the central NMR transition of quadrupolar nuclei with half-integer spin is achieved by applying a hyperbolic-secant π-inversion (sechinv) pulse to the satellite transitions. In combination with the quadrupolar Carr–Purcell Meiboom–Gill (QCPMG) pulse train, the sechinv pulse provides an additional signal enhancement of up to 2.7 for spin 3/2 nuclei in powdered solids. The 87Rb NMR enhancements realized using this experiment are compared to those obtained employing rotor-assisted population transfer (RAPT) and double frequency sweep (DFS) pulse experiments on magic angle spinning (MAS) powdered samples. In every case, the sequence employing sechinv pulses gives greater enhancements than the previously reported methods.

The kinetics and mechanism of probe-induced oxide growth on an octadecyltrichlorosilane (OTS) self-assembled monolayer (SAM) passivated native-SiO2/Si surface have been investigated using atomic force microscopy (AFM). It was found that oxidation strongly depends on tip polarity and the local chemistry of OTS molecules. At negative tip voltage, oxide grows and the oxidation involves a decomposition and depletion of OTS SAM. While under positive tip bias, OTS molecules are partially degraded. The dielectrical properties of the oxide were characterized by IV measurements using current sensing AFM. The barrier height of AFM grown oxide, in comparison with thermal oxide and OTS SAM, was determined. Current spikes relating to the release of single charge were also observed on the IV curves of AFM oxide.

A single π-bond captures 3, 4 and 5 atoms by Aleksey E Kuznetsov; Alexander I Boldyrev (452-456).
Could more than two atoms be bound in such a way that a π-bond is the major bonding force without involving σ-bond at all? To answer this question, we have shown that 3, 4 or 5 metal atoms can be held together by a single π-bond in the Mg3 , NaMg3 and Na2Mg3 species. In both the NaMg3 and Na2Mg3 species, the basic structural unit is an unusual Mg3 2− trigonal planar cluster, which exhibits properties of aromaticity, because it satisfies the 4n  + 2 rule for π-electrons and it is an equilateral triangle. Natural population analysis shows that the Na atomic orbitals contribute to formation of the π-bonding MO and thus all four in NaMg3 or all five in Na2Mg3 atoms are involved in chemical bonding. In these clusters, π-aromaticity occurs without initial formation of the σ-framework.

Microsolvation of the lithium ion by methanol in the gas phase by C.-C Wu; Y.-S Wang; C Chaudhuri; J.C Jiang; H.-C Chang (457-462).
Electrospray ionization (ESI) has been employed to produce Li+(CH3OH) m for infrared spectroscopic studies using a vibrational predissociation spectrometer. A gradual blue shift of the CO stretching frequency from 1023  cm −1 to 1027 cm−1 was observed as m increases from 5 to 10, supporting the suggestion for the formation of the second solvation-shell in Li+(CH3OH)5, in accord with the prediction by density functional theory calculations performed at the B3LYP/6-311+G**//6-31+G* level. We demonstrate in this work that the ESI source is applicable not only to the infrared study of Li+(CH3OH) m but also to other alkali metal methanol cluster ions as well.

Size-selective formation of tungsten cluster-containing silicon cages by the reactions of W n +  (n=1–5) with SiH4 by Akihiro Negishi; Naoki Kariya; Ko-ichi Sugawara; Ichiro Arai; Hidefumi Hiura; Toshihiko Kanayama (463-467).
The reactions of tungsten clusters, W n +  (n=1–5), with silane and their sequential reactions were investigated using FTICR mass spectrometry. It was found that the Si or SiH2 addition to the clusters, accompanied by H2 release, occurred for every collision with silane and then suddenly stopped at the specific silicon atom numbers of m: m=12 for n=1, m=17 and 18 for n=2, m=22 for n=3, m=25 and 26 for n=4 and m=29 for n=5. These values coincide with the surrounding atom numbers of a simple close packing model, suggesting the formation of stable silicon cages encapsulating tungsten clusters.

Wide and low angle neutron scattering of water–pyridine mixtures by Imre Bakó; G Pálinkás; J.C Dore; H Fischer; P Jóvári (468-472).
Neutron scattering measurements were performed for a number of water–pyridine mixtures using hydrogen/deuterium substitution for water. Composite partial pair correlation functions were extracted using the MCGR procedure. The results show changes in the water structure compared to the pure liquid and specific water–pyridine and pyridine–pyridine interactions. There is a strong scattering at low Q-values (<0.4 Å−1) which varies with pyridine concentration. These results are interpreted in terms of spherical clusters within the water matrix.

The aqueous solution conformation of model disaccharide, 4-O-α-d-xylopyranosyl-α-d-xylopyranose, was investigated using a combined quantum mechanical (QM)/molecular mechanical (MM) potential. In vacuo and aqueous solution conformational free energy surfaces were constructed from potential of mean force calculations, using weighted histogram analysis of 8.5 and 13.5 ns combined QM/MM molecular dynamics simulations, respectively. Calculations suggest a proportion of direct (5%) and water-bridged (34%) intersaccharide hydrogen bonds in aqueous solution, the latter consistent with a broad range of ϕψ space. Mulliken analysis indicates non-uniform polarisation of carbohydrate electron density, contrasting with electrostatic descriptions employed in force fields based on uniform over-polarisation at the HF/6-31G* level of theory.

Abnormal dispersion of polymer films in the THz frequency region by Naoto Nagai; Ryoichi Fukasawa (479-482).
Transmission and reflection measurements on various polymer films were performed in the THz frequency region, and the dielectric function was calculated by the Debye model to interpret the data. The ε 0 and ε obtained in our analysis show good agreement with the ε 0 from the electric measurements in MHz–GHz frequency region, and the ε calculated from the refractive index in the visible region. The abnormal dispersion was confirmed to appear in the THz frequency region, and the dispersion was not observed in non-polar polymers. This evidence shows the dispersion is due to the orientation polarization of polymers.

In this paper, we study the immobilization of DNA on boron-doped diamond (BDD) thin films for DNA hybridization analysis. Taking advantage of the conducting nature of the BDD film, a thin layer of polyaniline/poly (acrylic acid) (PANI/PAA) composite polymer film could be readily electropolymerized onto the diamond surface. The carboxylic acid residues in the polymer film act as the binding sites for DNA attachment, whilst the conductive polymer matrix enhances the electron-transfer between DNA and the diamond surface. Fluorescence microscopy and cyclic voltammetry measurements indicate that the polymer-modified BDD has minimal non-specific DNA adsorption, and provides a stable transduction platform for DNA sensing.

The low-temperature well-resolved 4T2g  →  4A2g fluorescence spectrum of Cs2NaYF6:Cr3+ is presented and interpreted. Strong vibrational progressions in the α 1g symmetric stretching and ε g stretching modes are based upon the zero phonon line and odd-parity vibronic origins. The Jahn–Teller stabilization energy in the 4T2g state is 255 cm−1. The Cr3+ emission has previously been assigned to Tm3+ upconversion. The 4T2g barycentre is strongly linearly correlated with metal–halogen distance for Cr3+ diluted into elpasolite hosts. More generally, for Cr3+ in other hosts, the metal–ligand distance divided by ligand formal charge exhibits a fairly linear relation with 4T2g4A2g energy separation, by contrast with the independence upon 2Eg4A2g energy separation.

Author Index (494-503).