Chemical Physics Letters (v.428, #4-6)
Editorial Board (CO2).
Rotational energy transfer in H2 + H2 by Renat A. Sultanov; Dennis Guster (227-230).
H2 + H2 rotational state-resolved cross-sections and thermal rates are calculated within close-coupling quantum-mechanical approach. Two recently published potential energy surfaces are applied.Quantum-mechanical close-coupling calculations for state-to-state cross-sections and thermal rate coefficients are reported for H2 + H2 collisions. Two recently developed potential energy surfaces (PESs) for the H2–H2 system are applied, namely, the global potential surface from the work [A.I. Boothroyd et al., J. Chem. Phys. 116 (2002) 666], and a restricted, model surface from the work [P. Diep and J.K. Johnson, J. Chem. Phys. 113 (2000) 3480; P. Diep, J.K. Johnson, J. Chem. Phys. 112 (2000) 4465]. The low temperature limit is investigated. We found significant differences in cross-sections and corresponding thermal rate coefficients calculated with these two PESs.
Keesom coefficients in gases by Valerio Magnasco; Michele Battezzati; Arnaldo Rapallo; Camilla Costa (231-235).
T-dependent long-range Keesom coefficients are evaluated up to the R −10 term for the homodimers of simply polar axially symmetric molecules. The corresponding attractive energies are the isotropic electrostatic contributions to the interaction energy and are temperature-dependent, and are found of importance when compared with the corresponding induction and dispersion energy results. T-dependent long-range Keesom coefficients are evaluated up to the R −10 term for small values of the dimensionless parameter | a ℓ ℓ ′ | . For large values of | a ℓ ℓ ′ | corrections must be introduced mostly for the dipole–dipole term, the correct values of C 6 being best obtained from a recently derived asymptotic formula. The corresponding attractive energies are the isotropic electrostatic contributions to the interaction energy and are temperature-dependent. Comparison with long-range induction and dispersion energy results for some simple polar axially symmetric molecules in the gas phase shows that at R = 10a 0 and T = 293 K the electrostatic dipole–dipole component is dominant for ∣a 11∣ > 0.5. For centrosymmetric molecules the corresponding electrostatic contribution is usually negligible with respect to dispersion.
Jet cooled rotational spectrum of methyl lactate by Paolo Ottaviani; Biagio Velino; Walther Caminati (236-240).
The structure of the most stable configuration of methyl lactate is precisely determined by rotational spectroscopy in supersonic expansions. The hydroxyl group acts as a proton donor to the carbonyl group.We report here the measurements of the rotational spectra of the main, O-d and four 13C species of methyl-lactate. They have been obtained by free jet millimeter-wave absorption and molecular beam Fourier-transform microwave spectroscopy. Only lines of the most stable conformer, the one with the hydroxyl group acting as a proton donor to the carbonylic group oxygen, have been observed. The V 3 barrier to internal rotation of the CH3–O methyl group has been determined to be 4.84(2) kJ mol−1. The experimental conformational and structural information are compared to those given by MP2/6-311++G(d, p) calculations.
Correlated wave functions for the ground state of the atoms Li through Kr by E. Buendía; F.J. Gálvez; A. Sarsa (241-244).
Variational Monte Carlo simulation of the probability distribution function of the atomic 3d orbital. In this Letter, we have calculated the correlation energy of the ground state of the atoms Li through Kr starting from explicitly correlated wave functions by using Variational Monte Carlo.The ground state of the atoms Li through Kr has been studied by using explicitly correlated wave functions along the variational Monte Carlo method. The variational wave function is the product of a Jastrow correlation factor, which accounts for dynamic correlations among the electrons, times a model function, which provides the correct properties of the exact wave function. The model wave function has been obtained within the parameterized optimized effective potential (POEP) framework. Some non-dynamic correlations due to near-degeneracy effects have been also considered for a number of atoms by means of a multiconfigurational model wave function.
Isomers of cyanodiacetylene: Theoretical structures and IR spectra by Marcin Gronowski; Robert Kołos (245-248).
An extensive DFT study on possible HC5N isomers yielded seven lowest energy species, of direct interest to the photochemistry of cyanodiacetylene, an astrophysically-relevant molecule. Coupled-clusters CCSD(T) geometries and relative energies are given for these isomers together with B3LYP-predicted IR spectra. Attention is drawn to the importance of branched structures.Coupled-clusters CCSD(T)/cc-pVTZ calculations have been carried out on several lowest energy isomers of cyanodiacetylene H–CC–CC–CN, previously selected in an extensive DFT study. Apart from the izonitrile H–CC–CC–NC, branched species CC(H)CCCN and CCCC(H)CN are found to be of particular importance, less stable than cyanodiacetylene by 48.5 and 51.0 kcal/mol, respectively. Harmonic frequencies and IR absorption intensities of vibrational fundamentals were predicted at the B3LYP/aug-cc-pVTZ level.
QTAIM study of the protonation of indole by Nicolás Otero; María J. González Moa; Marcos Mandado; Ricardo A. Mosquera (249-254).
QTAIM atomic and bond properties as well as delocalization indices computed on B3LYP/6-311++(2d, 2p) and MP2/6-31++G(d, p) electron densities are employed to explain the protonation preference of indole for C3 site.QTAIM atomic and bond properties as well as delocalization indices computed on B3LYP/6-311++(2d, 2p) and MP2/6-31++G(d, p) electron densities are employed to explain the protonation preference of indole for C3 site. In spite of displaying a very small increase of its total electron population, N1 is significantly stabilized in the preferred protonation due to an important loss of π electron population slightly exceeded by an increase of σ one. C2 and C8 are the atoms that reflect the largest changes of electron population in all C-protonations. 6-centre delocalization indices indicate that the preferred protonation increases the aromaticity of the benzenoid ring.
Explaining the sequence of protonation affinities of cytosine with QTAIM by María J. González Moa; Marcos Mandado; Ricardo A. Mosquera (255-261).
A qualitative scheme based on QTAIM results is described and applied to explain the sequence of protonation affinities shown by cytosine.The results obtained in the QTAIM electron density analysis carried out on B3LYP/6-31G(d, p) full optimized electron densities of the main protonated forms of cytosine indicate that the most stable ones display the largest electron transferences from hydrogens to the ring atoms. QTAIM results contradict the description of the resonance model, but are in line with a proposed qualitative scheme that relates the variations of atomic electron populations to their relative position with regard to the proton.
Ab initio and variational transition state approach to atmospheric photooxidation: Mechanism and kinetics for the reaction of HN3 with OH radicals by Shanqing Li; Qingzhu Zhang; Wenxing Wang (262-267).
In this Letter, ab initio molecular orbital calculations have been employed to investigate the mechanism for the atmospheric photooxidation of HN3 by OH radicals. The rate constants have been deduced by canonical variational transition state theory (CVT) with small-curvature tunneling (SCT) correction over a wide temperature range of 200–3000 K. The calculated results were in reasonable agreement with experimental measurement.Azide is readily protonated in the aqueous environment to yield volatile hydrazoic acid (HN3) that can then pose an airborne hazard. The reaction with OH radicals is likely tropospheric removal process of HN3. In this Letter, ab initio molecular orbital calculations have been employed to investigate the mechanism for the atmospheric photooxidation of HN3 by OH radicals. The rate constants have been deduced by canonical variational transition state theory (CVT) with small-curvature tunneling (SCT) correction over a wide temperature range of 200–3000 K. The calculated results were in reasonable agreement with experimental measurement.
Characterization of violet emission from Rb optical pumping cells used in laser-polarized xenon NMR experiments by Indrajit Saha; Panayiotis Nikolaou; Nicholas Whiting; Boyd M. Goodson (268-276).
Under certain conditions, high-power near-IR laser irradiation of Rb optical pumping cells used for generating laser-polarized xenon can exhibit bright visible emission resulting from energy pooling, collisions, and ionization processes.Visible emission from Rb optical pumping cells was characterized under a range of conditions relevant to the production of laser-polarized xenon (including temperature, partial pressures, and D1-resonant 795 nm laser power). Bright 421 nm (6P → 5S) emission was consistent with energy-pooling processes of the type: Rb∗(5P1/2) + Rb∗(5P1/2,3/2) → Rb∗(6P1/2,3/2) + Rb(5S1/2), with processes transiting through 5D states likely contributing at higher temperatures/lower N2 partial pressures. Under such conditions a number of Rb lines may be observed, indicating population of Rb states to ⩾9D (∼31 822 cm−1). Such energies exceed those required for efficient production of laser-induced plasma.
High-level ab initio calculations on the NiO2 system by J. Song; E. Aprá; Y.G. Khait; M.R. Hoffmann; K. Kowalski (277-282).
Several high-level ab initio methods were employed in studies of the narrow singlet-triplet separation of the cyclic form of nickel dioxide. The results obtained with the LR-CCSD(T) approach are in agreement with those produced by the MRCISD and DFT methods.Several high-level ab initio methods were employed in studies of the narrow singlet-triplet separation of the cyclic form of nickel dioxide (NiO2). It is shown that the complete versions of the locally renormalized coupled cluster method with singles, doubles, and noniterative triples (LR-CCSD(T)) approach, in contrast to the standard CCSD(T) method, provides results in concert with predictions of the density functional theory (DFT) and internally contracted multi-reference configuration interaction method (IC-MRCI), which favor the triplet state to be the lowest one. Relevant discussion of several aspects related to the underlying CCSD calculations, indicate that the dominant role of singly excited amplitudes violates the paradigm about the leading role of two-body effects in the description of the correlation energy. We also show that the multireference perturbation theory, exemplified here by the Generalized Van Vleck Perturbation Theory, requires the use of very large model space in order to properly describe the non-dynamical correlation effects.
Abnormal pinning of the Fermi and vacuum levels in monomolecular self-assembled films by Heejoon Ahn; Michael Zharnikov; James E. Whitten (283-287).
Ultrathin organic monomolecular films are generally believed to be in electrical contact with a photoelectron spectrometer when adsorbed on metal substrates. However, it is demonstrated that vacuum level instead of Fermi level alignment occurs between the substrate and adsorbate layer.Ultrathin organic monomolecular films, while electric insulators, are generally believed to be in electrical contact with a photoelectron spectrometer when adsorbed on metal substrates due to electron tunnelling that results in alignment of the Fermi levels of the film and the spectrometer. We show, however, that this generally applicable model is incorrect for these systems and that energy level alignment in photoemission experiments occurs in a complex fashion, involving both vacuum and Fermi levels of the monomolecular film, conductive substrate, and the spectrometer.
Dynamics of bromate oscillators with 1,4-cyclohexanedione in a continuously fed stirred tank reactor by Klára Keresztúri; István Szalai (288-292).
Bistability, periodic and aperiodic oscillations are observed in the bromate-1,4-cyclohexanedione-ferroin reaction operated in a continuously fed stirred tank reactor.The dynamics of the bromate-1,4-cyclohexanedione reaction and its ferroin catalyzed version in a continuously fed stirred tank reactor are reported. In the ([Br−]0, [H2SO4]0) and ([Br−]0, [ferroin]0) planes steady-state bistability and oscillations are observed. Close to the upper [Br−]0 limit of the oscillatory domain the oscillations become aperiodic. By increasing the [ferroin]0 the characteristic of the oscillations switches from ‘uncatalyzed’ to ‘catalyzed’-type. Additionally, the effects of the bromide ions and ferroin on the batch dynamics are investigated.
Mode-softening of C–H stretch vibration in alkyl groups on Ag(1 1 1) and the fluorination effect by Weixin Huang; Zhiquan Jiang; J.M. White (293-297).
We demonstrate for the first time the fluorination effect on the C–H stretch mode-softening of alkyl groups on Ag(1 1 1), which provides the evidence that the partial charge-donation, instead of the formation of an agostic C–H ⋯ M bond, is responsible for the C–H stretch mode-softening of adsorbed hydrocarbons/alkyl fragments on transition metal surfaces.The surface vibrations of CH2(a), CH3CH2(a) and CF3CH2(a) groups on Ag(1 1 1) have been studied by reflection–adsorption infrared spectroscopy. Compared with the corresponding iodides, obvious C–H stretch mode-softening was observed for adsorbed CH2(a) and CH3CH2(a), but not for CF3CH2(a), which is attributed to the weakening of the charge transfer from silver to the C–H anti-bond of the alkyl fragments by the fluorine atoms. These results provide the indirect evidence that the partial charge-donation into the C–H anti-bond, instead of the formation of an agostic C–H ⋯ M bond, is responsible for the C–H stretch mode-softening of adsorbed hydrocarbons/alkyl fragments on transition metal surfaces.
Influence of pressure on the photopolymerization rate of the linear orthorhombic polymer of C60 by K.P. Meletov; V.A. Davydov; A.V. Rakhmanina; V. Agafonov; J. Arvanitidis; D. Christofilos; K.S. Andrikopoulos; G.A. Kourouklis (298-302).
The photopolymerization of the orthorhombic C60 polymer has been studied by Raman spectroscopy as a function of laser intensity at ambient and high pressure conditions. The Raman spectra at ambient pressure, excited by 514.5 nm, show irreversible changes at intensity ∼3200 W/cm2, while at high pressure the transformation rate increases and the required intensity drops to ∼470 W/cm2. Raman spectra recorded after pressure release, indicate that non-irradiated sample sites do not exhibit any changes. In addition, ambient pressure X-ray diffraction measurements on high-pressure treated, non-irradiated samples show no structural modification, revealing the dominant role of light in the polymerization processes.The photopolymerization of the orthorhombic C60 polymer has been studied by Raman spectroscopy as a function of laser intensity at ambient and high pressure conditions. The Raman spectra at ambient pressure, excited by 514.5 nm, show irreversible changes at intensity ∼3200 W/cm2, while at high pressure the transformation rate increases and the required intensity drops to ∼470 W/cm2. Raman spectra recorded after pressure release, indicate that non-irradiated sample sites do not exhibit any changes. In addition, ambient pressure X-ray diffraction measurements on high-pressure treated, non-irradiated samples show no structural modification, revealing the dominant role of light in the polymerization processes.
Direct optical excitation of a fullerene-incarcerated metal ion by Mark A.G. Jones; R.A. Taylor; A. Ardavan; K. Porfyrakis; G.A.D. Briggs (303-306).
The endohedral fullerene Er3N@C80 shows characteristic 1.5 μm photoluminescence at cryogenic temperatures associated with radiative relaxation from the crystal-field split Er3+ 4I13/2 manifold to the 4I15/2 manifold. We present direct non-cage-mediated optical interaction with the erbium ion, and have used this to complete a photoluminescence-excitation map of the Er3+ 4I13/2 manifold.The endohedral fullerene Er3N@C80 shows characteristic 1.5 μm photoluminescence at cryogenic temperatures associated with radiative relaxation from the crystal-field split Er3+ 4I13/2 manifold to the 4I15/2 manifold. Previous observations of this luminescence were carried out by photoexcitation of the fullerene cage states leading to relaxation via the ionic states. We present direct non-cage-mediated optical interaction with the erbium ion. We have used this interaction to complete a photoluminescence-excitation map of the Er3+ 4I13/2 manifold. This ability to interact directly with the states of an incarcerated ion suggests the possibility of coherently manipulating fullerene qubit states with light.
Combination of phthalocyanine and fullerene moieties for optical limiting by James J. Doyle; Beatriz Ballesteros; Gema de la Torre; David A. McGovern; John M. Kelly; Tomás Torres; Werner J. Blau (307-311).
Nonlinear optical response of the molecules compounds 1 and 2 and C60, in solution, plotted with the normalised transmission as a function of laser pulse energy density.Z-scan experiments have been performed on solutions of tBu4PcTiO2-C60 (2) in order to explore a plausible synergistic effect. For comparative purposes we have also measured C60 and tBu4PcTiO (1) derivatives. The results indicate poorer excited-state absorption of dyad 2 than those of the corresponding individual phthalocyanine and fullerene components.
Photoluminescence properties and quantum size effect of ZnO nanoparticles confined inside a faujasite X zeolite matrix by C. Bouvy; W. Marine; R. Sporken; B.L. Su (312-316).
ZnO nanoparticles were grown inside a zeolite matrix by wet chemistry method. Under excitation with an ArF laser (193 nm), a strong blue-shift of the emission band of ZnO, suggesting a strong quantum size effect, is observed. The confinement of ZnO nanoparticles within a zeolite matrix improves the excitons stability.ZnO nanoparticles were grown inside a faujasite matrix by wet chemistry method. The structural and textural results by N2 adsorption, X-ray diffraction, 29Si and 27Al solid state NMR indicated successful incorporation of ZnO nanoparticles inside supercages of zeolite. After the incorporation, a slight structural symmetry change of the zeolite occurred. The photoluminescence of ZnO nanoparticles in zeolite matrix was studied by exciting the sample with an ArF laser (193 nm). A strong blue-shift of the emission band of ZnO, suggesting a strong quantum size effect, is observed. It is also revealed an improved stability of excitons when ZnO nanoparticles are confined within a zeolite matrix.
A density functional theory study on the effect of shape and size on the ionization potential and electron affinity of different carbon nanostructures by M.K. Shukla; Jerzy Leszczynski (317-320).
Density functional theory (DFT) investigations were performed to study the structures and properties of different carbon nanoclusters. The studies systems included carbon nano capsule, carbon nano bowl (one side close tube), carbon nano disk and fullerene. It was revealed that the computed electronic properties are significantly influenced by the shape and size of different carbon nanoclusters.Theoretical investigations were performed to study the structures and properties of different carbon nanoclusters. The computed properties were compared with those of the fullerene. The studied systems included carbon nano capsule, carbon nano bowl (one side closed tube), carbon nano disk and fullerene. The geometries of all species were optimized at the B3LYP level of theory using the 6-31G(d) basis set. Geometry of the silicon analog of fullerene (Si60) was also optimized at the same level of the theory. The HOMO–LUMO energy gap, ionization potential and electron affinity of studied clusters are reported and compared with those of the fullerene. It was found that the computed electronic properties are significantly influenced by the shape and size of different carbon nanoclusters.
Electronic structures of ferrocene-containing polymers by Yukihito Matsuura; Kimihiro Matsukawa (321-325).
Electronic structures of polymers, ferrocene (Cp2Fe, Cp = η5-C5H5) in the main chain, were examined using the tight-binding crystal orbital method with the extended Hückel approximation. Ferrocene-containing polymers with unsaturated carbon bridges had limited delocalization of the π electrons via the bridging moieties.Electronic structures of polymers, ferrocene (Cp2Fe, Cp = η5-C5H5) in the main chain, were examined using the tight-binding crystal orbital method. Attention was focused on the manner in which the band structures of the polymers were influenced by the bridging moieties between the ferrocenes. Ferrocene-containing polymers with unsaturated carbon bridges possessed relatively wide bandwidths of both the highest occupied band and the lowest unoccupied band. Although the π conjugation was broken at the iron atoms, the unsaturated carbon bridges could form limited delocalization of the π electrons between the neighbouring Cp rings via the bridging moieties.
Molecular packing and aggregation-induced emission of 4-dicyanomethylene-2,6-distyryl-4H-pyran derivatives by Hui Tong; Yongqiang Dong; Matthias Häußler; Yuning Hong; Jacky Wing Yip Lam; Herman H-Y. Sung; Ian D. Williams; Hoi Sing Kwok; Ben Zhong Tang (326-330).
From aggregation-induced quenching to aggregation-induced emission, completely different fluorescence properties of two 4-dicyanomethylene-2,6-distyryl-4H-pyran derivatives were examined in different solution and solid states to elucidate the effects of molecular structure and packing on their emission properties.Absorption and photoluminescence (PL) spectra of two derivatives of 4-dicyanomethylene-2,6-distyryl-4H-pyran were studied both in solution and in aggregation states. Although structurally similar, they show completely different emission behavior and an unusual aggregation-induced emission (AIE). Different molecular structure and packing are proposed as the major reason for these intriguing phenomena.
Interaction of a long molecular wire with a nanostructured surface: Violet Landers on Cu(2 1 1) by Letizia Savio; Leo Gross; Karl-Heinz Rieder; André Gourdon; Christian Joachim; Francesca Moresco (331-337).
Violet Lander (long molecular wire with legs) adsorbed at the Cu(2 1 1) surface. The scheme of the molecule is reported in the inset.Violet Lander molecules (long molecular wires with legs) are deposited on the nanostructured Cu(2 1 1) surface at 325 K and 177 K and investigated by low temperature scanning tunnelling microscopy. Selective population of (3 1 1) steps and local surface restructuring are observed for molecules adsorbed with their axis parallel to intrinsic steps. Thanks to the good matching between molecular dimensions and surface corrugation, molecules oriented perpendicularly to the steps assume conformations which allow tunnelling also through the molecular wire. The molecular wire terminations are hence self-contacted to the Cu(2 1 1) surface native (1 1 1) and (3 1 1) step edges.
Photoinduced electron transfer from anatase to rutile in partially reduced TiO2 (P-25) nanoparticles: An ESR study by Kenji Komaguchi; Haruka Nakano; Atsunori Araki; Yutaka Harima (338-342).
The photoeffects of trapped electrons in partially reduced TiO2 nanoparticles were studied by in situ ESR spectroscopy. The study revealed the preferential electron transfer from the anatase to the rutile phases in the TiO2 (P-25) particles upon illumination with an energy lower than the band gap at 77 K.The photoeffects of trapped electrons (Ti3+) in partially reduced TiO2 nanoparticles were studied by in situ ESR spectroscopy. For the pure phase samples, upon illumination with an energy lower than the band gap, the Ti3+ spectra decreased in intensity; however, the initial ESR signal was restored within 30 min in the dark at 77 K. For the TiO2 (P-25) particles, the ESR line shape changed significantly with being constant in the integrated intensity of the signal after the restoration. It was found that the trapped electrons can transfer from the anatase phase to the rutile phase in TiO2 (P-25) by photoexcitation.
Sonochemical synthesis of ferromagnetic core–shell Fe3O4–FeP nanoparticles and FeP nanoshells by C.G. Hu; Y. Li; J.P. Liu; Y.Y. Zhang; G. Bao; B. Buchine; Z.L. Wang (343-347).
Polycrystalline iron phosphide coated iron oxide and hollow iron phosphide nanoparticles were synthesized by sonichemistry. Structure analysis indicated that the diameters of these nanoparticles were less than 14 nm, and the core–shell and hollow nanoparticles are Fe3O4–FeP and FeP, respectively. Magnetic measurement demonstrated that both the core–shell Fe3O3–FeP and hollow FeP nanoparticles exhibited ferromagnetic behaviors.Polycrystalline iron phosphide coated iron oxide and hollow iron phosphide nanoparticles were synthesized by sonichemistry. Structure analysis indicated that the diameters of these nanoparticles were less than 14 nm, and the core–shell and hollow nanoparticles are Fe3O4–FeP and FeP, respectively. Magnetic measurement demonstrated that both the core–shell Fe3O4–FeP and hollow FeP nanoparticles exhibited ferromagnetic behaviors.
Hot-electron assisted reaction of p-nitrobenzoic acid adsorbed on metal–insulator–metal tunnel junction’s electrode surface by T. Wadayama; M. Yokawa (348-351).
The adsorbed PNBA− bands at the active junction’s area (A) increase in intensity with bias-voltage and a new band attributable to the azo-group emerges at voltages greater than +2.2 eV. In contrast, the non-active surface (B) shows no change. The results indicate that the anisotropic molecular surface can be fabricated.Surface-enhanced Raman scattering spectra of p-nitrobenzoic acid (PNBA) on the Ag electrode of a Ag/AlO x /Al tunnel junction are measured under application of a bias voltage. The bands caused by the adsorbed PNBA− at the active junction’s area increase in intensity with bias voltage and a new band attributable to the azo-group emerges at voltages greater than +2.2 eV. The intensity profile of the new band is similar to the junction’s Tafel plot. In contrast, the non-active electrode surface shows no change in the bands. These results indicate the tunnel junction might furnish a surface template for an anisotropic molecular structure.
A simple route to water-soluble size-tunable monodispersed Pd nanoparticles from light decomposition of Pd(PPh3)4 by Hua Tan; Tong Zhan; Wai Yip Fan (352-355).
Water-soluble monodispersed palladium nanoparticles of diameters 2.5, 5 and 10 nm controlled by varying the concentration of CTAB micelles have been prepared from light decomposition of Pd(PPh3)4.Water-soluble monodispersed palladium nanoparticles of diameters 2.5, 5 and 10 nm controlled by varying the concentration of CTAB (hexadecyltrimethylammonium bromide) micelles have been prepared from light decomposition of Pd(PPh3)4. The size and structure of these single crystalline particles have been confirmed using UV–vis spectroscopy, high resolution transmission electron microscope, energy dispersive X-ray analysis and powder X-ray diffraction methods.
Single-wall carbon nanotubes encaging linear chain C10H2 polyyne molecules inside by Daisuke Nishide; Hirofumi Dohi; Tomonari Wakabayashi; Eiji Nishibori; Shinobu Aoyagi; Masashi Ishida; Satoshi Kikuchi; Ryo Kitaura; Toshiki Sugai; Makoto Sakata; Hisanori Shinohara (356-360).
A new hybrid material C10H2@SWNTs, single-wall carbon nanotubes (SWNTs) encapsulating C10H2 polyyne molecules, has been synthesized and characterized by Raman spectroscopy. Being trapped inside the SWNTs, C10H2 molecules are shown to be stable well above 300 °C even under dry-air conditions.A new hybrid material C10H2@SWNTs, single-wall carbon nanotubes (SWNTs) encapsulating C10H2 polyyne molecules, has been synthesized and confirmed by Raman spectroscopy and X-ray diffraction measurement. The C10H2 polyyne molecules composed of linearly bonded sp-carbon atoms are aligned inside the SWNTs. This hybrid material exhibits a characteristic Raman signal at 2066 cm−1 attributable to the stretching vibration of the C10H2 molecules interacting with SWNTs. Being trapped inside the SWNTs, the otherwise unstable C10H2 molecules are shown to be stable well above 300 °C under dry-air conditions.
High-field magnetization of V15 cluster at ultra-low temperatures: Importance of antisymmetric exchange and its precise estimation by Alex Tarantul; Boris Tsukerblat; Achim Müller (361-366).
The low temperature adiabatic magnetization of the nanoscopic V15 cluster exhibiting a triangular spin-frustrated V 3 IV array is analyzed. The orientation of the antisymmetric (AS) exchange vector is shown to play crucial role in spin-frustrated systems. We were able for the first time to estimate precisely components of the AS vector.The low temperature adiabatic magnetization of the nanoscopic V15 cluster exhibiting a triangular spin-frustrated V 3 IV array is analyzed within the model that includes isotropic exchange interactions and antisymmetric (AS) exchange. Along with the absolute value of AS exchange the orientation of the AS vector is shown to play an important physical role in the spin-frustrated systems. We were able to reach a perfect fit to the experimental data on the stepwise magnetization vs. field in the whole temperature range and for the first time to estimate precisely two components of the AS vector, namely, in-plane and the perpendicular parts.
Effects of energetic stability in transport measurements of single benzene-dithiolate by the STM break junction technique by Satoru Tanibayashi; Tomofumi Tada; Satoshi Watanabe; Hideo Sekino (367-370).
The conductance behavior of the stretching processes in the STM break junction experiments was theoretically studied. The expected value of conductance computed with the three kinds of processes shows a flat plateau of conductance similar to the one observed by Xiao et al. [Nano Lett. 4 (2003) 267].The conductance behavior of the stretching processes in the STM break junction experiments was studied taking account of the effects of the energetic stability of the junction composed of benzene-dithiolate (BDT) and two Au(1 1 1) surfaces using the first principles calculations. The expected value of conductance computed with the three kinds of processes, including the one where only one junction is extended with tilted BDT, shows a flat plateau of conductance similar to the one observed by Xiao et al. [X. Xaio, B. Xu, N.J. Tao, Nano Lett. 4 (2003) 267] just before the break of the junctions.
Retardation of orientation relaxation of azo-dye doped amorphous polymers upon all-optical poling by S.W. Chan; J.-M. Nunzi; A. Quatela; M. Casalboni (371-375).
Relaxation of the all-optically induced orientation of azo-dyes in a polymer follows an unusual behaviour: it is inverted with respect to optically assisted orientation. We show that the polar orientation relaxation follows the duration of the all-optical poling process: the longer the poling, the slower the polar relaxation time.The orientation relaxation of azo-dyes upon all-optical poling was studied. Azo-dye doped amorphous polymers were poled for different durations by all-optical poling at several temperatures. A quasi-permanent macroscopic second-order nonlinear optical susceptibility χ (2) was inscribed in the dye-doped centrosymmetric polymer systems. Relaxation of the χ (2) was monitored by second harmonic generation. It shows that the polar orientation relaxation follows the duration of the poling process: the longer the poling, the slower the polar relaxation time. Causes of the orientation relaxation retardation are discussed.
Cobalt doped rings and cages of ZnO clusters: Motifs for magnetic cluster-assembled materials by A.C. Reber; S.N. Khanna; J.S. Hunjan; M.R. Beltrán (376-380).
First principles electronic structure studies have found that Zn12O12 cages are particularly stable units. When doped with a single Co or Fe atom, the doped units carry a magnetic moment of 3 and 4 μ B, respectively. Doping with two Co sites leads to ferromagnetically coupling due to direct exchange interaction.First principles electronic structure studies on pure and doped Zn n O n clusters have been carried out to identify elementary motifs with potential for cluster materials. In pure clusters Zn12O12 cages are shown to be particularly stable. When doped with a single Co or Fe atom, the doped units carry a magnetic moment of 3.0 μ B and 4.0 μ B, respectively. Doping of Zn12O12 with two Co sites leads to ferromagnetically coupled Co moments due to direct exchange interaction. It is proposed that the assemblies of such multiple doped units may lead to semiconductors with larger doping than attainable in bulk or films.
Supported Ni catalysts from nominal monolayer grow single-walled carbon nanotubes by Kazunori Kakehi; Suguru Noda; Shohei Chiashi; Shigeo Maruyama (381-385).
Ni catalysts tend to yield multi-walled carbon nanotubes when supported on substrates. We screened nominal Ni thickness on a SiO2 substrate and found that Ni nanoparticles did catalyze the growth of single-walled carbon nanotubes during chemical vapor deposition only when its nominal thickness was as thin as subnanometers.Fe, Co, and Ni are catalytically effective for growing single-walled carbon nanotubes (SWNTs). On substrates, however, Ni tends to yield only multi-walled carbon nanotubes. Because enhanced surface diffusion at the elevated growth temperature required for deposition might cause coarsening of Ni catalyst nanoparticles, adjusting the nominal Ni thickness should be crucial for controlling the particle size. Using our previously developed combinatorial method, we prepared a thickness profile of Ni on a quartz glass (SiO2) substrate and found that Ni nanoparticles catalyzed the growth of SWNTs by chemical vapor deposition only when nominal Ni thickness was in the monolayer range.
Growing fullerenes from seed: Growth transformations of fullerene polyhedra by Gunnar Brinkmann; Dieter Franceus; Patrick W. Fowler; Jack E. Graver (386-393).
A cut-and-paste approach using a family of structurally similar ‘growth patches’, and starting from a 24-vertex fullerene ‘seed’, allows formal construction of all fullerene isomers with up to at least 200 atoms.A cut-and-paste approach using a family of structurally similar ‘growth patches’ (pairs of non-isomorphic patches with the same boundary but containing different numbers of vertices) allows formal construction from a C24 seed of all fullerene isomers with up to at least 200 atoms. Algorithmic and chemical implications are discussed.
First-principles study of pentaerythritol tetranitrate single crystals under high pressure: Vibrational properties by W.F. Perger; Jijun Zhao; J.M. Winey; Y.M. Gupta (394-399).
The vibrational frequencies of the molecular crystal PETN are calculated at ambient and under hydrostatic pressure up to 4 GPa.First-principles theoretical methods were used to investigate the vibrational properties of pentaerythritol tetranitrate (PETN) under hydrostatic compression up to 4 GPa. Bond lengths and bond angles for the PETN molecules and the pressure–volume relation for the crystal under high pressure were calculated and compared with previous calculations and with experimental results. Based on the calculated optimized geometries at ambient conditions and under hydrostatic pressure, the frequencies of the internal vibrational modes of the PETN molecules in the crystal and pressure-induced frequency shifts of these vibrational modes were obtained. The calculated vibrational frequencies are compared with previous single molecule calculations and with experimental data.
Ligand design modulates photoinduced properties of cobalt-dioxolene valence tautomers by Alessandra Beni; Andrea Dei; David A. Shultz; Lorenzo Sorace (400-404).
Magnetic and EPR data suggest the occurrence of photoinduced Valence Tautomerism in a cobalt(III)-polydioxolene polymer. The 1D nature of the system results in a larger amount of cooperativity than previously observed in monomers. Analysis of kinetics data further suggest the existence of a relaxation mechanisms based on phonon assisted tunnelling.A cobalt(III)-polydioxolene polymer undergoing valence tautomeric interconversion was irradiated at cryogenic temperatures. Magnetic and EPR data suggest the occurrence of photoinduced VT interconversion, with a maximum degree of about 10%. The kinetics data evidence a larger amount of cooperativity than previously observed in simple monomer, a phenomenon that we attribute to the 1D nature of the system. In the range 9–40 K the relaxation time follows two different regimes, both temperature dependent. The small values of the activation energies suggest the existence of phonon assisted relaxation mechanisms based on a tunneling process involving the totalsymmetric breathing mode of the complex.
Spontaneous switching of permanent dipoles in single conjugated polymer molecules by Florian Schindler; John M. Lupton; Jochen Feldmann (405-410).
Electric fields applied in low temperature single molecule spectroscopy of conjugated polymers open a direct window to the microscopic charge distribution within the individual molecule. We typically observe a linear Stark effect, characteristic of either an internal electric field within the molecule or a difference in polarisation of ground and excited state. Here, we report evidence for spontaneous switching of the permanent dipole responsible for the shift in emission with field in a ladder-type polymer. This switching most likely results from photoinduced radical formation and annihilation and can be linked to blinking in single molecules and nanocrystal quantum dots.Electric fields applied in low temperature single molecule spectroscopy of conjugated polymers open a direct window to the microscopic charge distribution within the individual molecule. We typically observe a linear Stark effect, characteristic of either an internal electric field within the molecule or a difference in polarisation of ground and excited state. Here, we report evidence for spontaneous switching of the permanent dipole responsible for the shift in emission with field in a ladder-type polymer. This switching most likely results from photoinduced radical formation and annihilation and can be linked to blinking in single molecules and nanocrystal quantum dots.
Theoretical study of molecule mediated spin-polarized electron tunneling between magnetic materials by Haiying He; Ravindra Pandey; Shashi P. Karna (411-415).
Spin-polarized electron tunneling via a self-assembled monolayer of σ-bonded bicyclo[2.2.2]octane-1,4-dithiol on Ni(1 1 1) is calculated by first-principles methods. Comparison with a similar study involving π-conjugated molecules, suggests that the magnitude of the tunnel current and the spin-dependent current are strongly influenced by the nature of chemical bonds in the molecular structure.Spin-polarized electron tunneling between a Ni tip and a self-assembled monolayer, consisting of σ-bonded bicyclo[2.2.2]octane-1,4-dithiol molecules, deposited on Ni(1 1 1) surface is calculated by density functional approach within Bardeen, Tersoff, and Hamann formalism. The magnitude of the tunneling current is predicted to depend on the spin alignments of the probe tip and the substrate. Comparison with a similar study involving benzene-dithiol, a π-conjugated molecule, suggests that the magnitude of the tunnel current as well as the spin-dependent current is strongly influenced by the nature of the chemical bonds in the molecular structure.
Catalytic decomposition of n-heptane for the growth of high quality single wall carbon nanotubes by D. Grimm; A. Grüneis; C. Kramberger; M. Rümmeli; T. Gemming; B. Büchner; A. Barreiro; H. Kuzmany; R. Pfeiffer; T. Pichler (416-420).
High quality single wall carbon nanotubes (SWCNT) are grown using n-heptane as carbon feedstock and Ni/Co acetylacetonate catalyst precursors.A selective synthesis of clean SWCNT with an improved yield as well as individual SWCNT rooting from lithographically patterned catalyst islands at low temperatures is achieved.High quality single wall carbon nanotubes (SWCNT) were grown using n-heptane as the carbon feedstock and Ni/Co acetylacetonate catalyst precursors. They were characterized with regards to morphology, diameter distributions and yield using microscopic and spectroscopic techniques. n-Heptane provides a cheap and effective carbon source for the selective synthesis of clean SWCNTs at 680 °C with improved yield in comparison to other carbon sources. In addition we show the applicability of selective growth of individual SWCNTs rooting from lithographically patterned catalyst islands at this low temperature.
On wafer TiO2 nanotube-layer formation by anodization of Ti-films on Si by J.M. Macak; H. Tsuchiya; S. Berger; S. Bauer; S. Fujimoto; P. Schmuki (421-425).
Using a new technique, highly organized TiO2 nanotubular surfaces can be grown by the anodization of titanium on silicon substrates. The tubes are open at the top and their dimensions are given by the applied potential. The key to grow them is using temperatures close to 0 °C during anodization.In this work, we present the self-organized formation of anodic TiO2 nanotubular layers on flat and thin sputter-deposited layers of titanium on silicon. The TiO2 nanotubes were grown by anodization of these substrates in HF/H2SO4 electrolytes at different potentials between 5 V and 20 V resulting in tubes with diameter ranging from 30 to 100 nm. The key to achieve an ordered layer from the thin film samples is to operate at low temperatures. This results in a conversion efficiency of Ti to TiO2 nanotubes close to 100% and prevents loss of large amounts of the tubes due to chemical dissolution.
Preparation of Fe–Pt alloy particles by pulsed laser ablation in liquid medium by Yoshie Ishikawa; Kenji Kawaguchi; Yoshiki Shimizu; Takeshi Sasaki; Naoto Koshizaki (426-429).
Fe–Pt particles were prepared by pulsed laser ablation in degassed hexane and deionized water. The atomic composition of the obtained binary metal significantly depended on liquid media. Fe23Pt77 close to FePt3 and Fe38Pt62 which contributed to L10 phase formation were produced in hexane, however only Fe26Pt74 close to FePt3 was produced in water.Fe–Pt alloy particles were prepared by pulsed laser ablation in degassed hexane and deionized water. The atomic composition of the obtained binary metal particles significantly depended on the liquid media. Fe23Pt77 close to FePt3 and Fe38Pt62 which contributed to the L10 phase formation were produced in hexane, however only Fe26Pt74 close to FePt3 was produced in water. The absence of oxygen atoms in the molecule of the liquid medium was important because oxidation of iron species led to deviation from stoichiometric alloying. As-prepared particles produced in hexane had a random phase that was changed to the L10 phase by heat treatment at temperatures higher than 773 K.
Peierls instability and electron–phonon coupling in a one-dimensional sodium wire by Prasenjit Sen (430-435).
An atomic wire of Na does not have a Peierls instability over a range of inter-atomic distances. This may be due to a very small electron–phonon (EP) coupling in the wire. At larger interatomic distances, the EP coupling increases, and the wire undergoes a PT.We have studied Peierls instability in an atomically thin wire of sodium atoms using first-principles density-functional methods. A Na wire has a stable uniform linear structure over a range of inter-atomic distances. At smaller inter-atomic distances it develops a zigzag distortion. At larger inter-atomic distances, just before breaking, a Na wire undergoes a very weak Peierls dimerization. This Peierls transition in a Na wire is associated with a large increase in electron–phonon coupling.
Conformation-dependent hydrogen evolution with cobalt(II)tetraphenylporphyrin solubilized into poly(l-glutamate)–decylammonium ion complex by Pascaline Ngweniform; Yoshihumi Kusumoto; Miyuki Ikeda; Shouichi Somekawa; Bashir Ahmmad (436-439).
Visible light irradiation of a system consisting of cobalt(II)tetraphenylporphyrin, methylviologen, ethylenediaminetetraacetic acid disodium salt and Pt-loaded poly(l-glutamate) (Poly(Glu)) in aqueous decylammonium chloride (DeAC) solution, resulted in hydrogen production. The rate of hydrogen evolution depended on the change in the conformation of Poly(Glu) induced by the cooperative binding with DeAC.Hydrogen production was performed under visible light irradiation by using a system consisting of cobalt(II)tetraphenylporphyrin, methylviologen, ethylenediaminetetraacetic acid disodium salt and Pt-loaded poly(l-glutamate) (Poly(Glu)) in aqueous decylammonium chloride (DeAC) solution. The rate of hydrogen evolution depended on the change in the conformation of Poly(Glu) induced by the cooperative binding with DeAC.
Single nucleotide polymorphism analysis using different colored dye dimer probes by Nicole Marmé; Achim Friedrich; Dalia Denapaite; Regine Hakenbeck; Jens-Peter Knemeyer (440-445).
Fluorescence quenching by dye dimer formation has been utilized to develop hairpin-structured DNA probes for the detection of a single nucleotide polymorphism (SNP) in DNA sequences implicated in the penicillin resistance of Streptococcus pneumoniae. Depending on the target DNA either the green-labeled or the red-labeled DNA probe is opened and thus fluoresces.Fluorescence quenching by dye dimer formation has been utilized to develop hairpin-structured DNA probes for the detection of a single nucleotide polymorphism (SNP) in the penicillin target gene pbp2x, which is implicated in the penicillin resistance of Streptococcus pneumoniae. We designed two specific DNA probes for the identification of the pbp2x genes from a penicillin susceptible strain R6 and a resistant strain Streptococcus mitis 661 using green-fluorescent tetramethylrhodamine (TMR) and red-fluorescent DY-636, respectively. Hybridization of each of the probes to its respective target DNA sequence opened the DNA hairpin probes, consequently breaking the nonfluorescent dye dimers into fluorescent species. This hybridization of the target with the hairpin probe achieved single nucleotide specific detection at nanomolar concentrations via increased fluorescence.
Polaron dynamics in highly ordered molecular crystals by M. Hultell; S. Stafström (446-450).
We have studied polaron transport in highly ordered molecular crystals as a function of the intermolecular interaction strength, J. Our results show that there is a smooth transition from a nonadiabatic (upper) to an adiabatic (lower) polaronic drift process over the regime 20 < J < 120 meV.From a numerical solution of the time-dependent Schrödinger equation and the lattice equation of motion we obtain a microscopic picture of polaron transport in highly ordered molecular crystals in the presence of an external electric field. We have chosen the pentacene single crystal as a model system, but study the transport as a function of the intermolecular interaction strength, J. We observe a smooth transition from a nonadiabatic to an adiabatic polaronic drift process over the regime 20 < J < 120 meV. For intermolecular interaction strengths above ∼120 meV the polaron is no longer stable and the transport becomes band like.
Surface-enhanced infrared absorption spectroscopy using chemically deposited Pd thin film electrodes by Hiroto Miyake; Eiji Hosono; Masatoshi Osawa; Tatsuhiro Okada (451-456).
We report here the first observation of surface-enhanced infrared absorption (SEIRA) on chemically deposited Pd on Si. So far, SEIRA-active Pd thin films have been prepared by electrochemical deposition of Pd on SEIRA-active metals. The chemically deposited Pd film was able to remove the problem in the electrodeposited Pd.We report here the first observation of surface-enhanced infrared absorption (SEIRA) on chemically deposited Pd on Si. So far, SEIRA-active Pd films have been prepared by electrochemical deposition of Pd on SEIRA-active metals. When such films are used in solution to examine electrochemical reactions, however, Pd is dissolved into the solution at high potentials. The dissolution of Pd exposes the underlying metal surface and obscures the analysis of reactions on Pd surface. This problem can be removed by chemically depositing Pd directly onto the Si substrate. The strong SEIRAS effect of the chemically deposited Pd was demonstrated for CO adsorbed on the surface in acid under potential control. The dissolution of the Si substrate under anodic polarization is also discussed.
Measurement-assisted quantum dynamics control of 5-level system using intense CW-laser fields by M. Sugawara (457-460).
A new quantum control scheme using intense CW-laser fields together with quantum measurement is applied to Kobrak–Rice 5-level (KR5) quantum system. Population dynamics of the KR5 system under frequent measurements is clarified by effective Liouville equation . It is found that one can control stationary distribution by varying laser intensities.A new quantum control scheme using intense CW-laser fields together with quantum measurement is applied to Kobrak–Rice 5-level (KR5) quantum system. Population dynamics of the KR5 system under frequent measurements is clarified by effective Liouville equation. It is found that one can control the stationary population distribution that appears in t → ∞ limit by varying laser intensities.
Two new unitary-invariant and size-consistent perturbation theoretical approaches to the electron correlation energy by Reinhold F. Fink (461-466).
Using a second quantization representation of the Hamiltonian, an operator representation is derived which corresponds to the indicated partitioning of the CI-matrix in excitation degrees. This gives rise to a new Rayleigh–Schrödinger perturbation theory which is of comparable quality as the well established Møller–Plesset and Coupled-Cluster methods.Two Rayleigh–Schrödinger perturbation methods are proposed. In the first method, the unperturbed Hamiltonian is that part of the second quantization Hamiltonian that retains the number of electrons in the occupied orbital space. In the second method the electron-repulsion integrals (ERIs) with four non-occupied orbitals are substituted by ERIs with four occupied orbitals. Both approaches are size consistent and invariant with respect to unitary orbital transformations. Comparison of electronic energies with full CI, coupled-cluster, and Møller–Plesset results demonstrate that the new approaches are more accurate than Møller–Plesset perturbation theory and comparable with coupled-cluster results.
Author Index (467-475).