Chemical Physics Letters (v.397, #1-3)
Editorial board (IFC).
Anthracene derivative for a non-doped blue-emitting organic electroluminescence device with both excellent color purity and high efficiency by Silu Tao; Ziruo Hong; Zhaokuai Peng; Weigang Ju; Xiaohong Zhang; Pengfei Wang; Shikang Wu; Shuitong Lee (1-4).
A new anthracene derivative 2-tert-butyl-9,10-bis-(β-naphthyl)-anthracene (TBADN) was synthesized and used as a blue light-emitting material in a non-doped organic light-emitting diode (OLED). The OLED showed efficient blue emission with excellent Commission International de L’Eclairage (CIE) coordinates (x = 0.14, y = 0.10) and a maximum current efficiency of 2.6 cd/A. Compared with the prototypical blue OLEDs based on 9,10-bis-(β-naphthyl)-anthracene, the present device showed much improved color purity and efficiency. The improved performance is due to the reduction of molecular aggregation and the change of molecular electronic state by introducing of the bulky tert-butyl group on anthracene.
Influence of water on desorption rates of benzene adsorbed within single-wall carbon nanohorns by J. Fan; M. Yudasaka; Y. Kasuya; D. Kasuya; S. Iijima (5-10).
We analyzed the desorption of benzene adsorbed on single-wall carbon nanohorns (SWNHs) which have structures similar to single-wall carbon nanotubes. Two types of benzene-adsorption sites were found inside the SWNH tubules – the inner wall of sidewalls and that of tips. The amount of adsorbed benzene was greater at the former sites, while benzene adsorbed more strongly at the latter sites. We also found that the desorption-rate of benzene adsorbed inside the SWNHs that had been touched by water droplets or exposed to water vapor in advance became faster in dry air, but slowed in air saturated with water vapor.
A continuously recirculating optical pumping apparatus for high xenon polarization and surface NMR studies by Kevin Knagge; Jonathan Prange; Daniel Raftery (11-16).
A continuously recirculating xenon optical pumping apparatus was constructed and coupled to a 200 MHz NMR spectrometer. Steady-state 129Xe polarizations as high as 69% were achieved approximately 5 min after circulation was begun, and this polarization is >3.5 times larger than observed for single pass operation. Using this apparatus, spin polarization induced nuclear Overhauser effect (SPINOE) experiments were performed on porous silicon samples and on 13CD3OD adsorbed on TiO2-coated optical fibers to evaluate the capabilities of the system for studying low surface areas samples. The 13C enhancement achieved was approximately 14. The recirculating optical pumping system provides high xenon polarization at moderate laser powers for a variety of NMR studies.
Critical length of nanowires for hydrophobic behavior by Yu-Hung Cheng; Chung-Kuang Chou; Chih Chen; Syh-Yuh Cheng (17-20).
This Letter investigates the wetting behavior on surface with well-controlled nanoscale structure. Water and water–alcohol droplets were brought to contact the surface electroplated by Ag nanowires. It is found that hydrophobic behavior becomes more pronounced as the length of the nanowires increases. A critical length of approximately 100 nm is observed, beyond which the contact angle approaches a steady value of 130°. In addition, the contact angle of water levels off around 160° when the length of the fluorine-coated Ag nanowires exceeds the critical value of 100 nm. The mechanism of the hydrophobic behavior on surface with nanoscale structure is proposed.
Photofragment translational spectroscopy of nitric acid at 248 nm with VUV photoionization detection of products by M.J. Krisch; M.C. Reid; L.R. McCunn; L.J. Butler; J. Shu (21-25).
This study examines the 248-nm photodissociation of nitric acid (HNO3) and characterizes the translational energy distribution of the nascent photofragments. Photofragment translational spectroscopy with VUV photoionization detection evidenced one product channel, cleavage of HNO3 to form OH + NO2, and established an upper limit on the contribution from the O + HONO formation channel of 3%. These data contribute an independent measurement to a literature debate regarding the branching between these two channels.
Theoretical studies on the nature of uranyl–silicate, uranyl–phosphate and uranyl–arsenate interactions in the model H2UO2SiO4 · 3H2O, HUO2PO4 · 3H2O, and HUO2AsO4 · 3H2O molecules by D. Majumdar; K. Balasubramanian (26-33).
Extensive ab initio calculations have been carried out on the structure and spectra of H2UO2SiO4 · 3H2O, HUO2PO4 · 3H2O, and HUO2AsO4 · 3H2O. The calculated structures and vibrational spectra have been compared with the available experimental data. The nature of uranyl–anion (silicate, phosphate, and arsenate) bonding characteristics of these molecules is discussed.
Breaking N2 triple bond: the coupled-cluster corrected multi-reference configuration interaction description by L. Meissner; J. Gryniaków; I. Hubač (34-39).
The coupled-cluster corrections to multi-reference configuration interaction method with singles and doubles (MR-CISD) are applied to describe the N2 dissociation process which is a prototypical case of the triple-bond breaking. The exact solvability of the double-zeta N2 model used in the calculation permits comparison of results obtained within approximate schemes with the exact ones thus allows us to evaluate their performance. In our approach the MR-CISD method is corrected to improve description of the dynamic correlation thus an adequate selection of the MR-CISD reference space becomes an important factor for the successful application of the method. Several different reference spaces are tested.
Vibrational energy dynamics of water studied with ultrafast Stokes and anti-Stokes Raman spectroscopy by Zhaohui Wang; Yoonsoo Pang; Dana D. Dlott (40-45).
The transient Stokes Raman spectroscopy method is introduced to study the dynamics of OH-stretching vibrations in water excited by ultrashort infrared pulses. The combination of Stokes and anti-Stokes Raman probing allows the the absorption and emission contributions to be measured separately. Experiments with 3400 cm−1 pumping of OH-stretching of HOD solute in D2O solvent are reported. The Stokes Raman method is used to study the delay between the excited-state decay and the ground-state recovery, the vibrational Stokes shift, and the generation of weakened hydrogen bonding due to heat released by vibrational relaxation.
Direct experimental validation of the Jones–Ray effect by Poul B. Petersen; Justin C. Johnson; Kelly P. Knutsen; Richard J. Saykally (46-50).
In 1937, Jones and Ray observed a minimum in the surface tension of electrolyte solutions at ∼ 1 mM concentrations. According to the Gibbs adsorption equation, a decreasing surface tension corresponds to an enhanced ion concentration at the interface, which is contrary to textbook descriptions based on Onsanger–Samaras theory. The ‘Jones–Ray Effect’ has since been essentially dismissed as an artifact of the indirect experimental method used, and remains today as a curiosity. Here, we present direct experimental confirmation of the enhanced anion concentration around 1 mM of alkali iodide solutions using resonance enhanced femtosecond second harmonic generation, and the extraction of a large and negative value for the surface excess free energy (−6.2 ± 0.2 kcal/mol).
Confirmation of enhanced anion concentration at the liquid water surface by Poul B. Petersen; Richard J. Saykally (51-55).
The textbook view of the liquid electrolyte surfaces as being devoid of ions have recently been challenged by molecular dynamics simulations, which predict a surface enhancement of highly polarizable anions. Here we present the first direct experimental verification of this prediction. Enhanced azide ( N 3 - ) concentrations were measured at the liquid surface by femtosecond second harmonic generation (SHG) experiments exploiting the charge-transfer-to-solvent (CTTS) resonance of N 3 - , yielding a surface excess free energy of −9.9 ± 0.3 kJ/mole. Such surface-enhanced concentrations of anions could have important consequences for the chemical reactions taking place on atmospheric aerosols and at the ocean-air interface.
The parallel π–π stacking: a model study with MP2 and DFT methods by Xiangyu Ye; Zhen-Hua Li; Wenning Wang; Kangnian Fan; Wei Xu; Zhongyi Hua (56-61).
The parallel π–π stacking of benzene molecules was studied using Density Functional Theory (DFT) and second-order Moller–Plesset perturbation theory (MP2) methods. The DFT methods are proved to be inadequate in prediction of π–π stacking conformation and interaction energy. Cluster model calculations at the MP2/6-311 + G** level predicted an optimized conformation which is very close to the structure of the parallel-displaced benzene dimer. The calculated inter-plane distance of 3.3 Å is in good agreement with the observation in organic molecular crystals. The interaction energy predicted at MP2 level revealed that the pairwise interaction energy increases with the number of the parallel-stacked benzene molecules.
Ab initio study on the (O2–HCl)+ complex by Nobuaki Tanaka; Hiromasa Nishikiori; Tsuneo Fujii; Wade N. Sisk (62-66).
The (O2–HCl)+ complex has been investigated theoretically in the doublet and quartet states. Equilibrium structures have been calculated at the CCSD level of theory with the aug-cc-pVDZ and 6-311++G(2d,2p) basis sets. One non-planar and two planar complexes are found in the doublet and quartet states, respectively. The doublet state complex is predicted to possess the largest interaction energy and be the most stable. Natural bond orbital analysis revealed intermolecular charge transfers occur followed by intramolecular charge rearrangement. The calculated vibrational frequencies are compared with those observed in solid Ne.
Magnetic resonance imaging of a magnetic field-dependent chemical wave by Robert Evans; Christiane R. Timmel; P.J. Hore; Melanie M. Britton (67-72).
The magnetic field dependence of the travelling wave formed during the reaction of (ethylenediaminetetraacetato)cobalt(II) (Co(II)EDTA2−) and hydrogen peroxide was studied using magnetic resonance imaging (MRI). The reaction was investigated in a vertical tube, in which the wave was initiated from above. The wave propagated downwards, initially with a flat wavefront before forming a finger. Magnetic field effects were observed only once the finger had formed. The wave propagation was accelerated by a magnetic field with a negative gradient (i.e., when the field was stronger at the top of the tube than at the bottom) and slightly decelerated by positive field gradients.
Bulk Zn1 − x Co x O magnetic semiconductors prepared by hydrothermal technique by M. Bouloudenine; N. Viart; S. Colis; A. Dinia (73-76).
We have used a hydrothermal technique to synthesize polycrystalline Zn1 − x Co x O diluted magnetic semiconductor. The synthesis temperature was of 240 °C and the Co concentration of 10 at.%. X-ray diffraction indicates that the Co-doped ZnO thus prepared has the pure ZnO wurtzite structure without any significant change in the cell parameters. Optical absorption measurements show several absorption bands that are due to the transitions between the crystal-field-split 3d levels of tetrahedral Co2+ substituting Zn2+ ions. Room temperature magnetization measurements reveal a paramagnetic behavior for the Co-doped ZnO samples. This is attributed to the absence of free carriers.
Hydrogen adsorption in C60 at pressures up to 2000 atm by A.V. Talyzin; S. Klyamkin (77-81).
Hydrogen adsorption isotherms of crystalline C60 were measured in the temperature interval from 223 to 573 K and under hydrogen pressure up to 2000 atm. Only the 573 K isotherm exhibited evidence for chemisorption starting from ∼800 atm. Hydrogen adsorption for isotherms measured below 473 K appeared to be not saturated even at 2000 atm. Maximum observed adsorption for these isotherms is almost the same and corresponds to 1.6–1.8 H2 molecules per C60. In contrast to experiments performed at lower pressure, presented data can not be explained only by adsorption of single H2 molecule in octahedral sites of C60 structure.
An investigation of the HOMO electron density distribution of cyclopentene by electron momentum spectroscopy by X.G. Ren; C.G. Ning; J.K. Deng; S.F. Zhang; G.L. Su; H. Zhou; B. Li; G.Q. Li (82-86).
The highest occupied molecular orbital (HOMO) of cyclopentene (C5H8) has been studied by a binary (e, 2e) electron momentum spectroscopy, at an impact energy of 1200 eV plus the binding energy and using symmetric non-coplanar kinematics. The first measurements of the complete valence shell binding energy spectra and the HOMO momentum profile are reported. The experimental momentum profile of HOMO is compared with the theoretical momentum profiles calculated using Hartree–Fock and density functional theory method with various basis sets. The EMS experimental result is well described by the calculations.
Time-resolved transient electroluminescence measurements of emission from DCM-doped Alq3 layers by C.W. Ma; O. Lengyel; J. Kovac; I. Bello; C.S. Lee; S.T. Lee (87-90).
Organic light-emitting devices (OLEDs) using NPB (α-naphthylphenylbiphenyl diamine) as the hole-transport layer and DCM [4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran] doped Alq3[tris-(8-hydroxyquinoline)] as the emission layer were studied using a time-resolved transient electroluminescence method. Upon application of a pseudo-rectangular voltage pulse, the luminance increased and overshot to maxima. Using suitable spectrum filters the overshoot luminance peaks were identified to originate solely from the DCM emission. When two consecutive voltage pulses are applied, the overshoot vanished during the second pulse when time gap is shorter than 1 ms. It was considered to be related to carrier traps in the DCM molecules.
Engineering nanostructures for giant optical fields by Martin Moskovits; Dae Hong Jeong (91-95).
SERS spectra obtained from two nanostructures are reported. In the first, silver nanoparticles are assembled using a dithiol molecular linker into small clusters appropriately structured to produce strong local electromagnetic (em) fields in the interstitial regions between neighboring nanoparticles, precisely where the molecular linker resides. The second consists of bifurcated silver nanowires, predicted to show strong enhancements in the cleft of the bifurcation when excited by light polarized across the cleft. The results suggest that the giant SERS enhancements needed for near-single-molecule sensitivity largely result from extraordinarily intense local em fileds at geometrically favorable locations in nanostructures.
Two-dimensional nuclear magnetic resonance spectroscopy in optically pumped semiconductors by Anil Patel; Clifford R. Bowers (96-100).
Optical pumping enhanced double quantum nuclear spin coherences were detected in bulk GaAs and InP by two-dimensional NMR. The stimulation of the coherences was achieved using a single non-selective resonant RF pulse. This is unusual because stimulation of such coherences from a spin system at thermal equilibrium in high field would normally require a minimum of two pulses. A density matrix analysis, combined with a time-resolved study of the build-up of the double quantum coherence in GaAs, suggests that the enhancement of the double quantum coherence amplitude stems from optical pumping of dipolar nuclear spin order.
Anomalous doping effect on Ag-doped DNA conductor by H. Mayama; T. Hiroya; K. Inagaki; S. Tanda; K. Yoshikawa (101-105).
We report novel experimental results of chemical doping effect on Ag-doped DNA conductor. The prepared Ag-doped DNA samples were confirmed by EXAFS that Ag+ was doped into π-way. In I–V measurements at room temperature, nonlinear I–V curves with hysteresis emerged and systematic change in electrical conductivity σ was observed from 10−10 to 10−6 Ω−1 cm−1 under doping condition [Ag+]/[Base pair] = 10−6−10. The relation between the conductivity and dopant concentration showed a weak dependence σ ∝ [Ag+]0.5. This ‘weakly doping effect’ may be caused by the long-range correlated randomness of sequence in DNA, in contrast with usual doped organic conductors.
Gaussian weighting in the quasiclassical trajectory method by Laurent Bonnet; Jean-Claude Rayez (106-109).
In standard quasiclassical trajectory calculations, each trajectory has the same statistical weight. Alternately, the Gaussian weighting method is an ad hoc procedure which consists in weighting each trajectory by a Gaussian-like coefficient such that the closer the final actions to integer values, the larger the coefficient. The goal of the present note is to justify such a method in the framework of classical S matrix theory.
Excited-state processes in protochlorophyllide a – a femtosecond time-resolved absorption study by B. Dietzek; R. Maksimenka; T. Siebert; E. Birckner; W. Kiefer; J. Popp; G. Hermann; M. Schmitt (110-115).
The excited-state dynamics of protochlorophyllide a, a porphyrine like compound and precursor of the chlorophyll biosynthesis, was studied by femtosecond absorption spectroscopy. Three kinetic components with time constants of 4, 27 and 200 ps are found to be involved in the excited-state decay. According to similar kinetic processes observed in the ultrafast dynamics of prophyrins, the 4-ps component is attributed to vibrational relaxation leading to thermal equilibrium in the lowest excited singlet state. The 27- and 200-ps processes are suggested to correspond with the decay via a second decay channel into the electronic ground state.
Experimental characterization of the Ne + ICl(X,ν″ = 0) and Ne + ICl(B,ν′ = 2) multi-dimensional intermolecular potentials by David B. Strasfeld; Joshua P. Darr; Richard A. Loomis (116-122).
Multiple features associated with transitions of the near T-shaped and linear Ne⋯I35,37Cl(X,ν′ = 0) conformers are observed in laser-induced fluorescence spectra recorded in the ICl B–X, 2–0 and 3–0 spectral regions. The T-shaped complexes access the lowest intermolecular vibrational level, n b ′ = 0 , within the Ne + ICl(B,ν′) potential, while the linear complexes access four intermolecular bending levels, n b ′ = 1 – 4 , that form a progression of features up to the Ne + ICl(B,ν′) dissociation limit. The binding energy of the energetically more stable, ground state linear Ne⋯I35Cl(X,ν″ = 0) conformer is measured to be 84(1) cm−1 in action spectroscopy experiments.
Selective ionization via different electronic pathways by optimal control demonstrated for 23Na39K/23Na41K by Albrecht Lindinger; Franziska Vetter; Cosmin Lupulescu; Mateusz Plewicki; Stefan M. Weber; Andrea Merli; Ludger Wöste (123-127).
Selective optimization of different isotopomers in an ionization process with shaped fs-laser pulses is presented for 23Na39K/23Na41K. By employing evolution strategies in a closed feedback loop a considerably high enhancement by a total factor of about 25 of one isotope compared to the other and reversed is measured. Surprisingly, vibrational levels of differing electronic states are utilized for the different isotopomer selections. Our approach generally allows to influence vibrational wave functions by coherent interaction with the corresponding spectral pulse components on the fs-time scale.
Polymer-assisted synthesis of aligned amorphous silicon nanowires and their core/shell structures with Au nanoparticles by Xing-bin Yan; Tao Xu; Shan Xu; Gang Chen; Qun-ji Xue; Sheng-rong Yang (128-132).
Aligned amorphous Si nanowires (SiNWs) were synthesized directly from Si substrates with the assistance of a new carbon-based network polymer, poly(phenylcarbyne), during the heat-treatment in Ar atmosphere at 1120 °C. A core/shell structure of SiNWs wrapped with Au nanoparticles was simply fabricated as well. The analytic results of the morphology and microstructure confirmed the orientation and the amorphous nature of the SiNWs, and the high dispersion of Au nanoparticles on the surface of the SiNWs without any aggregation. The formation of the SiNWs was explained on the basis of the reaction of carbon with the native silica layer covering Si substrates.
Structure diagram of gold nanoparticles in solution under irradiation of UV pulse laser by Fumitaka Mafuné (133-137).
Gold nanoparticles with 10 nm average diameter were prepared in aqueous solutions of sodium dodecyl sulfate (SDS) at prescribed concentrations. A solution containing nanoparticles was irradiated with a focused pulse laser at 355 nm. The nanoparticles were either fragmented under irradiation into those with 2.5 nm average diameter or formed nano-scale networks, depending on the SDS concentration and the laser fluence. A structure diagram of the products after irradiation, constructed as functions of the concentration and the fluence, provided information on the mechanism of fragmentation and formation of nanonetworks.
Structure of solid-supported lipid–DNA–metal complexes investigated by energy dispersive X-ray diffraction by G. Caracciolo; C. Sadun; R. Caminiti; M. Pisani; P. Bruni; O. Francescangeli (138-143).
When mixing aqueous solutions of DNA and dioloeyl-phosphatidylcholine multilamellar liposomes in the presence of Mn2+ ions, a multilamellar liquid-crystalline phase is formed in which DNA monolayers are comprised between opposing lipid bilayers. Here, we report on a new experimental procedure resulting in the formation of solid-supported DOPC–DNA–Mn2+ complexes in the biologically relevant excess water condition. The supramolecular structure of solid-supported complexes, characterized by means of Energy Dispersive X-ray Diffraction, exhibits very similar structural properties with respect to the solution structure of the complexes as revealed by synchrotron Small Angle X-ray Scattering measurements.
Thermodynamical viability of the reactions of DMSO with OH, O2 and O3 atmospheric oxidants and a test of the IB extrapolation method by Paula de Souza Sombrio; Jaqueline Ceolin de Bona; Stella Maris Resende (144-147).
The thermochemistry of the reaction of dimethyl sulfoxide with OH, O2 and O3 was investigated at a highly correlated ab initio level of theory. For the OH radical, channels that lead to CH3S(O)CH2 + H2O, CH3S(O)OH + CH3 and CH3SO + CH3OH products are spontaneous. All possibilities studied for the reaction with O2 are non-spontaneous. The reaction channels with O3 producing CH3SO + CH3OOO and CH3S(O)2CH3 + O2 are thermodynamically favorable. The performance of the IB method for reaction energies containing sulfur compounds was investigated, and the results show that this extrapolation is not as efficient as expected, producing results of accuracy intermediate between cc-pVTZ and cc-pVQZ levels.
Substituent and solvent effects on the UV/Vis absorption spectra of 5-(4-substituted arylazo)-6-hydroxy-4-methyl-3-cyano-2-pyridones by Gordana S. Ušćumlić; Dusanˇ Z.ˇ Mijin; Nataša V. Valentić; Vlatka V. Vajs; Biljana M. Sušić (148-153).
Absorption spectra of ten 5-(4-substituted arylazo)-6-hydroxy-4-methyl-3-cyano-2-pyridones have been recorded in fifteen solvents in the range 200–600 nm. The substituents at the phenyl nucleus are as follows: OH, OCH3, CH3, C2H5, H, Cl, Br, I, COOH and NO2. The effects of substituents on the absorption spectra of investigated compounds are interpreted by correlation of absorption frequencies with simple Hammett equation. The effects of solvent polarity and solvent/solute hydrogen bonding interactions are analyzed by means of linear solvation energy relationships concept proposed by Kamlet and Taft. The azo-hydrazone tuatomeric equilibration is found to depend upon substituents as well as on solvents.
Efficient calculation of the structural and electronic properties of mixed valence materials: application to Prussian Blue analogues by Jacek C. Wojdeł; Stefan T. Bromley (154-159).
Mixed valence materials containing the same atom type in different spin and/or oxidation states, although displaying great applications potential, present a considerable challenge to accurate efficient electronic structure calculations employing ultra-soft pseudo-potentials (USPPs). Ideally USPPs should aim for full transferability between all centres of the same atom type. Via examining an archetypal class of mixed valence materials (Prussian Blue analogues) we show: (i) using a single USPP appears be a non-transferable approach for the mixed valence centres and (ii) such materials can be treated via a mixed-USPP approach whereby each mixed valence centre type is assigned a suitable USPP.
The ionization and dissociation mechanisms of pyridine–ammonia hydrogen bonding complex by Tujin Shi; Jianhong Ge; Jingzhong Guo; Qihe Zhu (160-168).
The energetics, geometrical structures, ionization process, dissociation channels of pyridine-ammonia (Py⋯NH3) and the corresponding cation complexes are investigated with ab initio theory. Vertical ionization potentials (vIPs) were calculated at the spin projection UMP2/6-31G(d,p) (PUMP2/6-31G(d,p)) level. During the relaxation process, the vertically ionized complex can gain some excess energy, which makes relevant dissociation channels favorable. The potential energy surface of the rearrangement processes and the dissociation channels were calculated at B3LYP/6-31G(d,p)//R(U)HF/6-31G(d,p) level, showing that when the Py⋯NH3 is vertically ionized, the dissociation into PyH+ and NH2 is the dominant channel. Also, the rearrangement processes (proton transfer) were investigated in detail by moving the proton along the hydrogen bond.
Ultraviolet photoelectron spectra of Ti2@C80 by Kentaro Iwasaki; Shojun Hino; Daisuke Yoshimura; Baopeng Cao; Toshiya Okazaki; Hisanori Shinohara (169-173).
Ultraviolet photoelectron spectra of metallofullerene Ti2@C80 were measured using a synchrotron orbital radiation light source. The band intensity of the Ti2@C80 spectra was found to be dependent on the incident photon energy, similar to observations for other fullerenes. The spectral onset energy was 0.8 eV below the Fermi level, and was comparable to that of Ca@C82, but smaller than that of the empty C80. Using comparisons between UPS and molecular orbital calculations, the number of electrons transferred from the titanium atom to C80 was estimated.
Some comments on the coupled cluster with generalized singles and doubles (CCGSD) ansatz by Debashis Mukherjee; Werner Kutzelnigg (174-179).
In this Letter, we present some comments on the nature of the CCGSD ansatz Ψ = e T Φ for an n-electron wave function, with T a linear combination of general one- and two-particle operators. Nooijen had conjectured that such a parameterization is possible for the exact eigenstate Ψ. We point out that the essential reason for the invalidity of this conjecture lies in the fact that the basis operators into which the Fock space Hamiltonian can be expanded, are not closed under commutation, i.e. do not span a Lie algebra. We give two proofs, based, respectively, on the variation principle and the method of moments, to show this. The variational proof traces the same ground as in an earlier one by Nakatsuji, which did not get the due recognition. We, however, formulate it in such a way that the key role of the algebra of the operators of T becomes transparent. We also discuss a related proof of Mazziotti. Our second proof sheds further light on why the ansatz, while not exact, might still provide an accurate description of a many-electron state, as has been found in some recent computational studies. We also discuss two recent attempts to disprove the exactness of the ansatz, based on a dimensionality argument.
Theoretical study on all-metal aromatic complexes: interaction with small gas molecule by Xingbang Hu; Haoran Li; Wanchun Liang; Shijun Han (180-184).
The recent advance of the aromaticity concept into the all-metal species enlightens us to explore whether all-metal aromatic system Al 4 2 - can adsorb small gas molecule on its surface. Y ( Y = Al 4 2 - , LiAl 4 - and Li 2 Al 4 ) and X (X = H2, N2, O2, F2, Cl2, Br2, CO and SO) were chosen for this purpose. When interacting with X, the similarities and differences between all-metal aromatic system Al 4 2 - / LiAl 4 - / Li 2 Al 4 and organic aromatic systems were discussed. Some special phenomena of Y⋯X induced by the characteristic of Al 4 2 - were investigated, which may give a base for the future research on the potential catalysis of these complexes.
Theoretical investigations of the C–H⋯N interactions and molecular electrostatic potentials: aza derivatives of cubane by Nilesh R. Dhumal; Shridhar P. Gejji (185-193).
Weak C–H⋯N interactions, which are electrostatic in nature, in a series of aza derivatives of cubane, (CH)8 − α N α (α = 1–7) have been investigated by employing the ab initio and hybrid density functional methods. The characteristics of interactions have been analyzed using the topography of the molecular electrostatic potential, which reveal shallow minima near nitrogen on encompassing from the lowest energy isomers of azacubane to heptaazacubane. From the natural bond orbital analysis it has been shown that nitrogen lone pair localization increases on encompassing from aza to heptaazacubane. Consequent C–H stretching frequencies, particularly their red and blue shifts, have been discussed.
Spectroscopy and thermodynamics of LiS/NaS (X2Π and A2Σ+) and LiS+/NaS+(X3Σ− and A3Π) by Edmond P.F. Lee; Timothy G. Wright (194-199).
Potential energy curves are calculated for the X2Π and A2Σ+ states of LiS and NaS and the X3Σ− and A3Π states of LiS+and NaS+. The RCCSD(T)/aug-cc-pVXZ levels of theory are employed (X = Q, 5 and ∞), where the ∞Z results are obtained at each bond distance, R, employing a two-point extrapolation to the basis set limit. From the three sets of curves, spectroscopic constants, ionization and dissociation energies are derived. Comparison is made to available experimental and calculational results.
Molecular reorientation in assembled CO structures and contrast inversion in STM by Eeva Niemi; Jouko Nieminen (200-204).
Recent scanning tunneling microscopy experiments [S. Zöphel, J. Repp, G. Meyer, K.-H. Rieder, Chem. Phys. Lett. 310 (1999) 145; A.J. Heinrich, C.P. Lutz, J.A. Gupta, D.M. Eigler, Science 298 (2002) 1381] for CO on Cu(1 1 1) and Cu(2 1 1) surfaces show CO monomers as dark depressions, whereas dimers and trimers appear as bright patterns. The dark image of a monomer has been shown to result from a destructive interference between two tunneling paths [J. Nieminen, E. Niemi, K.-H. Rieder, Surf. Sci. 552 (2004) L47]. In this Letter, we show how switching between tunneling channels within the through molecule path can be induced by reorientation of a molecule. Hence, a destructive interference between through vacuum and through molecule paths can be reversed into constructive interference by manipulating the adsorbate geometry.
Evidence for hydrogen bond-like C–H–O interactions in aqueous 1,4-dioxane probed by high pressure by Hai-Chou Chang; Jyh-Chiang Jiang; Ching-Wei Chuang; Sheng Hsien Lin (205-210).
We have investigated the effect of pressure versus C–H–O interactions in 1,4-dioxane/D2O mixtures. Hydrogen bond-like C–H–O interaction may be a distinct possibility to understand the origin of the spectral features observed under high pressure. Based on the results of density functional theory calculations, the structural identification of the pressure-induced hydrophobic isomers is complicated by the presence of more than one stable isomeric form. This study demonstrates that high pressure can be used as a valuable means of triggering hydrogen bond-like C–H–O interactions.
The effect of thickness, pore size and structure of a nanomembrane on the flux and selectivity in reverse osmosis separations: a molecular dynamics study by Sohail Murad; Ludwig C. Nitsche (211-215).
Molecular dynamics simulations examine the effect of pore size, structure and membrane thickness on flux and selectivity in reverse osmosis. Membranes are modeled using layers of barrier molecules tethered harmonically to periodic lattice sites. Permeation occurs within a Knudsen like regime where close confinement in nanopores precludes water–water interactions, leaving water–pore interactions to determine hydraulic resistance. Results show the solvent flux to be rather insensitive to an appropriately defined tortuosity. Ion selectivity seems to correlate primarily with overall hydraulic resistance, irrespective of the number of membrane layers.
Dynamics of photoisomerisation and rotational relaxation of 3,3′-diethyloxadicarbocyanine iodide in room temperature ionic liquid and binary mixture of ionic liquid and water by Debdeep Chakrabarty; Anjan Chakraborty; Partha Hazra; Debabrata Seth; Nilmoni Sarkar (216-221).
The dynamics of photoisomerisation and rotational relaxation of 3,3′-diethyloxadicarbocyanine iodide (DODCI) in room temperature ionic liquid (IL) and binary mixture of IL and water are investigated using steady state and time resolved fluorescence spectroscopy. The photoisomerisation rate of DODCI is drastically retarded in room temperature IL 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) compared to isopolar solvent. The rotational relaxation time of the same dye is much slower in IL compared to the isopolar conventional solvent and become faster in presence of traces amount of water. The activation energy for photoisomerisation in different media (IL and IL-water) is also determined.
A theoretical model to calculate linear electro-optic effect in crystals by Chuangtian Chen; Huatong Yang; Zhizhong Wang; Zheshuai Lin (222-226).
A simplified theoretical model is suggested to deal with the phonon–electronic coupling process and then to calculate electro-optic coefficients in which the interaction between the lattice vibrations induced by low frequency external electric field and electrons can be contributed. Results show that the dominant contribution to the electro-optical effect should be ascribed to the new correction term deduced from interaction between lattice vibrations and electron motion, rather than the pure electron contribution. The differences of the magnitude of the correction for different materials mainly come from the differences of their static dielectric constants.
Upconversion luminescence from Nd3+-doped gerimania-ormosil organic–inorganic hybrid films derived at low temperature by Wenxiu Que; X. Hu (227-232).
Nd3+-doped germania-ormosil hybrid films are synthesized by a sol–gel spin-coating technique for photonic applications. Acid-catalyzed solutions of γ-glycidoxypropyltrimethoxysilane mixed with gemanium isopropoxide are used as matrix precursors. Planar waveguide films with a thickness of about 1.8-μm are obtained by a single spin-coating process and at low temperature heat treatment. The effects of Nd3+ doping concentration and heat treatment temperature on upconversion emission of the hybrid films are studied. An intense room-temperature violet upconversion emission at 397 nm is observed from the hybrid film with an optimum Nd3+ concentration of 0.5 mol% upon excitation with a yellow light at 584 nm.
Shear viscosity of simple fluids in porous media: molecular dynamics simulations and correlation models (II) – methane in silicate pores by Hui Zhang; Bing-jian Zhang; Jing-jun Zhang (233-236).
As a continuation of our last paper [Chem. Phys. Lett. 350 (2001) 247], the shear viscosity of fluid methane in silicate porous media have been calculcated using equilibrium molecular dynamics simulations, and two similar correlation models are also presented which can describe the viscosity value under different densities, temperatures and pore widths.
Photodecomposition reaction of trapped aniline cation by photofragment excitation spectroscopy by Keiko Kato; Kaoru Yamanouchi (237-241).
A photofragment excitation spectrum of aniline cation, C 6 H 5 NH 2 + , was measured in the range of 450–400 nm by ion-trap mass spectrometry. The trapped cations exposed to a nanosecond laser field (I ≈ 1 MW/cm2, Δt ≈ 10 ns) absorbed two photons and dissociated into C 5 H 6 + efficiently in the 427–417 nm range. From a comparison with the photoelectron spectrum of neutral aniline, it is identified that the photodissociation of aniline cation into C 5 H 6 + proceeds via the second electronically excited ( B ˜ 2 B 1 ) state.
Low velocity experiments for collision energy dependence of partial ionization cross-sections of C2H2 with He*(23S) metastable atoms by Takuya Horio; Takuro Hatamoto; Naoki Kishimoto; Koichi Ohno (242-246).
Collision energy dependence of partial ionization cross-sections of C2H2 by collision with He*(23S) metastable atoms in low collision energy regions (20–50 meV) was first observed using a liquid N2 cooled discharge nozzle source. Negative collision energy dependence was found for ionizations from σCH molecular orbitals, while positive collision energy dependence has been obtained in higher collision energy region of 100–360 meV. These results can be explained by the anisotropic interaction of the present system, and especially the low collision energy feature should indicate that a shallow attractive well exists around hydrogen atom.
Unique graphical representation of protein sequences based on nucleotide triplet codons by Milan Randić; Jure Zupan; Alexandru T. Balaban (247-252).
We consider a graphical representation of proteins as an alternative to the usual representation of proteins as a sequence listing the natural amino acids. The approach is based on a graphical representation of triplets of DNA in which the interior of a square or the interior of a tetrahedron is used to accommodate 64 sites for the 64 codons. By associating a zigzag curve and various matrices with a protein, just as was the case with graphical representation of DNA, one can construct selected invariants to serve as protein descriptors. The approach is illustrated on the A-chain of human insulin.
Effect of the symmetric stretch on the dipole polarizability of the cyclic form of the ozone molecule: a study based on high-level ab initio and density functional theory calculations by Anastasios Haskopoulos; George Maroulis (253-257).
We have calculated the effect of the symmetric stretching on the dipole polarizability (α αβ ) of the cyclic form of ozone, O3(D3h). We have used both conventional ab initio and density functional theory methods. All basis sets have been especially designed for polarizability calculations on O3(D3h). At the CCSD(T)/[9s6p5d1f] level of theory the α αβ invariants change rapidly around R e = 1.444 Å as α ¯ ( R ) / e 2 a 0 2 E h - 1 = 16.49 + 8.68 ( R - R e ) + 0.38 ( R - R e ) 2 - 2.63 ( R - R e ) 3 + 0.51 ( R - R e ) 4 , Δ α ( R ) / e 2 a 0 2 E h - 1 = - 6.79 - 7.93 ( R - R e ) + 0.32 ( R - R e ) 2 + 2.15 ( R - R e ) 3 . The B3LYP, B3P86 and B3PW91 density functional theory methods agree quite well with the most accurate conventional ab initio values for the mean polarizability at R e but tend to overestimate the magnitude of the anisotropy. The same trend is very much obvious for the derivatives ( d α ¯ / d R ) e and (dΔα/R)e.
Non-linear optical response of single carrier 2-D anharmonic quantum dots by Manas Ghosh; Ram Kuntal Hazra; S.P. Bhattacharyya (258-264).
A linear variational route is explored for computing the first non-linear polarizability (β) of single carrier quantum dots with anharmonicity in the confinement potential. Variations in β with variations in the strength of the confining potential (ω 0), the perpendicular magnetic field strength (ω c) and the strength of a specific form of anharmonic coupling (λ) are analyzed. A 2 × 2 model is used to predict analytically the nature of λ, ω c and ω 0 dependence of β and compare with what is obtained from a more detailed calculation.
Oscillations and period-doubling bifurcations in the electrochemical oxidation of thiourea by Liangqin Xu; Qingyu Gao; Jiamin Feng; Jichang Wang (265-270).
The electrochemical oxidation of thiourea on a Pt electrode was found to exhibit both simple and period-doubled oscillations. Measurements of the potentiostatic I/Ø behavior and impedance spectra suggest that the studied system belongs to the hidden negative differential resistance (HNDR) oscillator. The dependence of complex oscillations on initial compositions of the reaction mixture and temperature has also been characterized, which showed that: (1) lowering the reaction temperature facilitates the occurrence of complex oscillations; (2) the frequency of oscillation increases linearly with respect to the temperature; and (3) hydrochloric acid exhibits stronger influence on the reaction behavior than nitric acid.
Insight into carbon nanotubes-template reaction at high temperature by Long Hu; Y.X. Li; X.X. Ding; C. Tang; S.R. Qi (271-276).
Different types of carbon nanotubes (CNTs), including multi-walled CNTs, single-walled CNTs bundles, isolated single- or double-walled CNTs and nano-bamboo structured CNTs, were used as the templates to synthesize SiC and BN one-dimensional nanostructures within the framework of high-temperature CNTs-template reaction. We found that the structures of SiC and BN products weakly depend on the topology of the used CNTs. BN can completely maintain the starting topology of CNTs, while the hollow CNTs collapsed to SiC nanowires with solid interiors. The involved reaction mechanisms were discussed based on TEM observations for the products synthesized from the different reaction sources.
A new model for the molecular structure of supported vanadium oxide catalysts by Onno L.J. Gijzeman; Joost N.J. van Lingen; Joop H. van Lenthe; Stan J. Tinnemans; Daphne E. Keller; Bert M. Weckhuysen (277-281).
Raman spectroscopy experiments found the V＝O stretching frequency for the supported VO4 species to decrease with increasing catalyst temperature. Calculations on the vibrational frequencies of several models using density functional theory show that a consistent description of the experimental data can be obtained if we assume that the VO4 species are anchored to the oxidic surface by one V–O bond only, in contrast to the traditional pyramidal model, which assumes three V–Osupport bonds and one V＝O. The proposed VO3 structure points away from the surface and consists of one V＝O unit and an active oxygen ‘molecule’ loosely bound to the vanadium atom, a peroxide species.
Polarized spectral analysis of Nd3+ ions in LaB3O6 biaxial crystal by Yujin Chen; Xiuqin Lin; Zundu Luo; Yidong Huang (282-287).
Nd3+:LaB3O6 crystal has been grown by the Czochraski method and the accurate concentration of Nd3+ ions in the crystal was measured. The orientation relationship between the crystallographic axes and optical axes was determined. The polarized absorption spectra, polarized fluorescence spectra and fluorescence decay curve of Nd3+ ions in the LaB3O6 crystal were measured at room temperature. Some important spectroscopic parameters were obtained based on the Judd–Ofelt theory and the Fuchtbauer–Ladenburg formula. The discussions about the effect of crystal structure on the spectroscopic properties of Nd3+ ions were given.