Chemical Physics Letters (v.406, #4-6)
Editorial board (CO2).
Configuration interaction singles method with multilayer fragment molecular orbital scheme by Yuji Mochizuki; Shigeru Koikegami; Shinji Amari; Katsunori Segawa; Kazuo Kitaura; Tatsuya Nakano (283-288).
We have developed a parallelized integral-direct solver for configuration interaction singles (CIS) in the Abinit-mp program, by accepting the recently proposed multilayer fragment molecular orbital (MLFMO) method. In the MLFMO–CIS scheme, the region of interest in photoactive issues can be treated with the environmental potential at the Hartree–Fock (HF) level. The parallel efficiency is observed to be reasonable for the formaldehyde hydration system. A realistic applicability of the method is demonstrated for the photoactive yellow protein (PYP) including 125 amino acid residues.
Laser-based synthesis of core Ag-shell AgI nanoparticles by Hua Tan; Wai Yip Fan (289-293).
A laser-controlled synthesis of silver iodide (AgI) nanoparticles with isolable AgI shell–Ag core stable intermediates is achieved via molecular iodine photodissociation in the presence of pure Ag nanoparticles dispersed in water. Ag nanoparticles were introduced into the solution containing sodium dodecylsulphate surfactants and iodine by ablating a piece of silver foil with a 532 nm pulsed Nd-YAG laser. Transmission electron microscopy images showed that different AgI shell–Ag core sizes could be achieved by controlling the photolysis of I2 in solution. These nanoparticles were also found to catalyse an atom-economy Grignard–Barbier organic reaction.
Electronic structure calculations of radical reactions for poly(methyl methacrylate) degradation by Patrick F. Conforti; Barbara J. Garrison (294-299).
The hybrid CBS-QB3 electronic structure approach is used to calculate the reaction energetics for decomposition reactions of radicals formed from UV radiation of the polymer poly(methyl methacrylate) (PMMA). Relative to the photon created radical species, the decarboxylation reaction to form CO2 is exothermic whereas the reaction to form CO is endothermic. For degradation of the polymer in low-Earth orbit (LEO) conditions, the synergy of the reaction with O(3P) atoms is considered. The addition of O atoms to all of the radicals is exothermic, leading in many cases to the formation of a stable molecule and another radical species.
The enthalpy of the O–H bond homolytic dissociation: Basis-set extrapolated density functional theory and coupled cluster calculations by B.J. Costa Cabral; Sylvio Canuto (300-305).
The O–H bond homolytic dissociation of water, hydrogen peroxide, methanol, phenol, and cathecol is investigated by density functional theory (DFT) and ab initio coupled cluster calculations. DFT results are based on several recently proposed functionals, including B98, PBE, VSXC, and HCTH. The dependence of DFT results on the basis-set size is discussed using correlation-consistent polarized (cc-pVXZ) basis-sets (X = 2–5). A scheme proposed by Truhlar is used to extrapolate CCSD energies. Basis-set extrapolated CCSD results for the O–H bond homolytic dissociation enthalpies of phenol and cathecol are in excellent agreement with experimental information.
Density functional study of the TiO2–dopamine complex by Manuel Vega-Arroyo; Pierre R. LeBreton; Tijana Rajh; Peter Zapol; Larry A. Curtiss (306-311).
The binding energies and excitation energies of dopamine interacting with TiO2 clusters of different sizes representing an anatase surface are calculated. Results indicate that bidentate adsorption of dopamine on undercoordinated sites containing a Ti＝O double bond is more stable than monodentate or molecular adsorption on the (1 0 1) anatase surface. A large red shift in the absorption spectrum of TiO2–dopamine is calculated, in agreement with experimental studies. We also investigate how the optical properties of TiO2–dopamine are affected by adding carboxyl thymine and subsequent base pairing with adenine.
A new perspective on the mechanism of asymmetric amplification by Kouichi Asakura; Tetsuya Yamamoto; Sawako Inoue; Shuichi Osanai; Dilip K. Kondepudi; Tomohiko Yamaguchi (312-317).
A mechanism of asymmetric amplification, i.e., chemical reaction in which enantiomeric excess, ee, of a product is higher than that of chiral auxiliary for catalyst, was investigated. The reaction rate and the ee of the product differed significantly when the order of reagent addition was changed. A kinetic model formulated to explain this phenomenon predicted that the ee of the product should vary during the reaction. Our experimental investigation indeed found the variation of ee predicted by this theoretical model. There has been no previous report observing such a variation in ee during asymmetric amplification and a different ee produced by changing the order of reagent addition.
The MP2 energy as a functional of the Hartree–Fock density matrix by Péter R. Surján (318-320).
The explicit E [P] functional is presented, where E  is the second order Møller–Plesset correlation energy and P is the standard Hartree–Fock density matrix. The ideas leading to this functional are implicit in previous studies, but the significance of its existence has not yet been sufficiently emphasized and its simple explicit form has not been presented. With the proposed functional one may obtain the correlation energy in the absence of molecular orbitals, knowing merely the density matrix. This may further facilitate linear scaling computation of the correlation energy.
Entrance channel complexes of cationic aromatic SN2 reactions: IR spectra of fluorobenzene+–(H2O) n clusters by Ulrich Lorenz; Nicola Solcà; Otto Dopfer (321-326).
Microhydrated fluorobenzene cation clusters, C6H5F+–(H2O) n with n = 1 and 2, were characterized by IR photodissociation spectra in the O–H stretch range and UB3LYP/6-31G* calculations. The intermolecular C6H5F+–H2O potential features several minima with charge–dipole orientation and comparable binding energies (D 0 ∼ 9 ± 1 kcal/mol). The C6H5F+–H2O spectrum is consistent with a structure in which the O atom of H2O approaches the C6H5F+ cation from above the aromatic plane. The C6H5F+–(H2O)2 spectrum reveals the presence of two isomers, in which either a (H2O)2 dimer or two single H2O ligands are attached to C6H5F+. The detected C6H5F+–(H2O)1,2 complexes were unreactive with respect to nucleophilic substitution.
The influence of the structure of the radical cation dimer pair of aromatic molecules on the principal values of a g-tensor: DFT predictions by Alexander Petrenko; Kevin Redding; Lowell D. Kispert (327-331).
The density functional theory calculations were carried out to determine the influence of the structure of the radical cation dimer pair of model aromatic molecules on the principal values of a g-tensor. The calculated results for different model structures of (naphthalene)2 and (p-dimethylenebenzene)2 and individual model naphthalene and p-dimethylenebenzene molecules were analyzed by comparing results of calculations for different models. This comparison predicts an analogous effect for g-tensor principal values of P 700 + special dimer pair radical cation in core Photosystem I and for g-tensor principal values of the P 700 T special dimer pair triplet radical in core Photosystem I. The change in the g-tensor principal values in stacked structures of p-terphenyl cation radical was deduced from an extended model stacked multimer structure.
Molecular dynamics study of the ionic conductivity of 1-n-butyl-3-methylimidazolium salts as ionic liquids by Sang Uck Lee; Jaehoon Jung; Young-Kyu Han (332-340).
We have performed a molecular dynamics simulation to investigate the ionic conductivities of the 1-n-butyl-3-methylimidazolium salts [BMIM]+[Anion]− as ionic liquids, where the anions are PF 6 - and the fluorinated organic anions CF3COO−, C3F7COO−, CF 3 SO 3 - , and C 4 F 9 SO 3 - . We developed bonded force field parameters for the anions and applied them to the molecular dynamics simulations. The calculated ionic conductivities are qualitatively in good agreement with the experimental values, demonstrating that the volume and self-diffusion coefficient of ionic liquids are important factors in determining the ionic conductivity of ionic liquids.
Encapsulation of halide anions in perhydrogenated silicon fullerene: X−@Si20H20 (X = F, Cl, Br, I) by Fabio Pichierri; Vijay Kumar; Yoshiyuki Kawazoe (341-344).
We report the results of a density functional study of the encapsulation of halide anions into the dodecahedral cage of the perhydrogenated silicon fullerene Si20H20. The HOMO–LUMO energy gap of the endohedral complexes X−@Si20H20 (X = F, Cl, Br, I) is only ∼0.5 eV larger than that computed for the empty fullerene. The amount of charge that is being transferred from the encapsulated anion to the fullerene increases from F− (∼10%) to I− (>70%). Only the encapsulation of Br− does not alter the cage thus indicating that this spherical anion might be employed in the anion-templated synthesis of the elusive Si20H20 cluster.
Time-resolved kinetic studies on quenching of HCCl ( A ˜ 1 A ″ ( 040 ) ) by alkane and alcohol molecules by Xueliang Yang; Yunzhen Liu; Hailing Wang; Yang Chen; Congxiang Chen (345-350).
HCCl ( X ˜ 1 A ′ ) radicals were produced by laser photolysis of HCClBr2 at 213 nm, and were electronically excited to A ˜ 1 A ″ ( 040 ) at 617.97 nm with a dye laser pumped by a Nd:YAG laser. Experimental quenching data of HCCl ( A ˜ 1 A ″ ( 040 ) ) by alkane and alcohol molecules were measured at room temperature (293 K) by observing the time-resolved total fluorescence signals in a cell where the total pressure was 23.0 Torr. It was shown that the quenching rate constant of HCCl ( A ˜ 1 A ″ ( 040 ) ) by alkane molecules increase almost linearly with the number of C–H bonds contained in the homologous molecules. The formation cross-sections of the complexes between HCCl ( A ˜ 1 A ″ ) and quenchers were calculated by means of collision complex model and the attractive forces between the collision partners were considered to play an important role in the quenching processes of HCCl ( A ˜ 1 A ″ ( 040 ) ) by the quenchers studied in this work.
Theoretical study of the HCN–CH3 and HNC–CH3 radicals: Hydrogen and covalent bonding by M. Solimannejad; M.E. Alikhani (351-354).
The interaction between the methyl radical with hydrogen cyanide and hydrogen iso-cyanide is reported at several ab initio levels of theory. Four structures are studied: two hydrogen-bonded (H3C⋯HCN and H3C⋯HNC) and two covalent-bonded (H3C–NCH and H3C–CNH) structures. It is shown that hydrogen cyanide forms a weak hydrogen bond with the methyl radical ( D e CP = − 1.3 kcal / mol ) , while its covalent-bonded isomer is mostly unbound with respect to the fragments ground state ( D e CP = + 0.5 kcal / mol ) . The ground state of the hydrogen isocyanide complexed with the methyl radical is found to be a covalent-bonded complex ( D e CP = − 25.5 kcal / mol ) , whereas its hydrogen-bonded isomer is only a weak complex ( D e CP = − 2.2 kcal / mol ) .
Hydrogen bond stabilization in Diels–Alder transition states: The cycloaddition of hydroxy-ortho-quinodimethane with fumaric acid and dimethylfumarate by V. Tamilmani; C.A. Daul; J. Lage Robles; C.G. Bochet; P. Venuvanalingam (355-359).
DFT investigations on the mechanism of Diels–Alder reactions of a hydroxy-ortho-quinodimethane with fumaric acid derivatives were performed to understand the origin of the syn or anti configuration of the adducts. The diene hydroxyl group and the dieneophile carboxyl group show hydrogen bonding in the transition state, significantly favouring the syn product. This reaction is poorly diastereoselective for R = CO2Me (ratio syn/anti = 57:43) and significantly improved for R = CO2H (ratio syn/anti = 71:29). The stereoselectivities are properly predicted from transition structures calculated at the B3LYP/6-31G(d) level.
Preferential formation of mixed dimers in aluminium containing porphyrin–phthalocyanine systems: A photophysical study by Mário Rui Pereira; João A. Ferreira; Graham Hungerford (360-365).
The interaction of chloroaluminium phthalocyanine and aluminium porphyrin in solution was studied using UV–visible and fluorescence techniques. The spectra of the porphyrin alone exhibited new bands attributed to aggregates and a value of −12.6 kJ mol−1 for the enthalpy of dimerization was obtained. A small dimerization constant of 5.8 × 103 M−1 was found for phthalocyanine homodimers and preferential formation of mixed dimers over porphyrin homodimers was observed experimentally and supported by molecular modelling. k d and ΔH values of 5.7 × 104 M−1 and −21.1 kJ mol−1 were found in the mixed system, along with an enhancement in phthalocyanine fluorescence.
Hydroperoxy radical as hydrogen bond donor: NH3–HOO complex – ab initio and topological study by Andrzej Bil; Zdzisław Latajka (366-370).
This Letter analyses the hydrogen bond donor properties of the HOO radical. The NH3–HOO radical is examined by means of ab initio as well as topological methods. The obtained results are in good agreement with the conclusions given in an experimental paper devoted to the examination of this complex by means of IR spectroscopy in an argon matrix. In particular, present calculations confirm an open structure of this complex and the assignment of the observed bands. Anharmonic IR spectra for the complex are calculated. The necessity of distinction between geometry and structure of the complex is emphasized as the complex has an open structure and cyclic geometry.
Adiabatic corrections to the energies of 50 typical medium size molecules containing H atoms by José R. Mohallem; Cristina P. Gonçalves; Tathiana Moreira (371-374).
The adiabatic correction is calculated for a series of 50 typical medium size molecules containing H atoms, most of them for the first time. The effect increases with the size of organic compounds. For this kind of molecules it is found, as a general rule, that the adiabatic correction per electron is an almost constant value, amounting approximately 0.27 × 10−3 au.
Influence of extra-framework cations on the diffusion of alkanes in silicalite: Comparison between quasi-elastic neutron scattering and molecular simulations by Frédéric Leroy; Hervé Jobic (375-380).
Quasi-elastic neutron scattering (QENS) has been used to study the diffusion of n-octane in silicalite. A larger diffusivity is found when compared with previous experiments performed in Na–ZSM-5, by a factor of 4. MD simulations have been performed for n-butane, n-hexane, and n-octane in silicalite and in a model zeolite with atomic defects to mimic the steric hindrance due to extra-framework cations in ZSM-5. The new QENS measurements and the MD simulations explain to a large extent the discrepancy previously observed for n-octane in MFI-type zeolites.
Oriented silicon nanowires on silicon substrates from oxide-assisted growth and gold catalysts by Yuan Yao; Fanghua Li; Shuit-Tong Lee (381-385).
High-density, oriented silicon nanowires (SiNWs) array were fabricated on (0 0 1) silicon substrates by the oxide-assisted growth method assisted with Au catalyst in a hot filament chemical vapor deposition system. The yield of SiNWs was different with the synthesis temperature. Au particles were present at the tips of the SiNWs and limited the wire diameter. High resolution transmission electron microscopy revealed the epitaxial SiNWs on the Si substrate.
Electronic spectroscopy of anthracene molecules trapped in helium nanodroplets by Serge Krasnokutski; Gaël Rouillé; Friedrich Huisken (386-392).
The electronic spectroscopy of anthracene trapped in liquid helium nanodroplets has been studied in the spectral region of the S1 ← S0 transition using both laser-induced fluorescence and molecular beam depletion spectroscopy with mass spectrometric detection. The absorption band has been located at 27 625.9 cm−1, red-shifted by 61.4 cm−1 from the respective gas phase transition. It consists of two well separated maxima and a long tail to the blue side which is essentially assigned to the phonon wing. The origin of the band structure is discussed in this Letter.
An electron localization function study of the trimerization of acetylene: Reaction mechanism and development of aromaticity by Juan C. Santos; Victor Polo; Juan Andrés (393-397).
The reaction mechanism and the development of the aromaticity along the trimerization of acetylene to yield benzene have been analyzed by means of use of the electron localization function (ELF) and the catastrophe theory. The electronic rearrangements associated to bond breaking/forming processes are characterized by four catastrophes, which determine five domains of structural stability of the ELF topology along the intrinsic reaction path. The analysis of the ELF separated into in-plane (σ) and out-of-plane (π) contributions shows that the transition structure (TS) has a low σ electron delocalization, being π-aromaticity developed at the final stage of the reaction.
Evidence for blueshift by weak exciton confinement and tuning of bandgap in superparamagnetic nanocomposites by Swapna S. Nair; Mercy Mathews; M.R. Anantharaman (398-403).
Superparamagnetic nanocomposites based on γ-Fe2O3 and sulphonated polystyrene were synthesised by ion-exchange process and the structural characterisation has been carried out using X-ray diffraction technique. Doping of cobalt in to the γ-Fe2O3 lattice was effected in situ and the doping was varied in the atomic percentage range 1–10. The optical absorption studies show a band gap of 2.84 eV, which is blue shifted by 0.64 eV when compared to the reported values for the bulk samples (2.2 eV). This is explained on the basis of weak quantum confinement. Further size reduction can result in a strong confinement, which can yield transparent magnetic nanocomposites because of further blue shifting. The band gap gets red shifted further with the addition of cobalt in the lattice and this red shift increases with the increase in doping. The observed red shift can be attributed to the strain in the lattice caused by the anisotropy induced by the addition of cobalt. Thus, tuning of bandgap and blue shifting is aided by weak exciton confinement and further red shifting of the bandgap is assisted by cobalt doping.
Fate of several hydroxyalkyl isoprene radicals: Formation of hydroxycarbonyl compounds by Víctor M. Ramírez-Ramírez; Ignacio Nebot-Gil (404-408).
The fate of two hydroxyalkyl radicals derived from the oxidation of isoprene with OH radical, resulting in the formation of two hydroxycarbonyls, was investigated by means of theoretical quantum chemistry methods. All the stationary points were optimised at the UMP2/6-31G(d) level, and high-level ab initio calculations were performed at the QCISD(T)/6-31G(d) level of computation upon MP2 optimised structures in order to refine the energy of the molecules characterised. Our results show that the reaction of hydroxyalkyl radicals with O2 is a very favoured pathway that explains the formation of the two hydroxycarbonyls optimised.
Free energy and entropy calculations in the conformational equilibrium of 1,2-dichloroethane in water by Sergio Madurga; Eudald Vilaseca (409-414).
Using Monte Carlo free energy perturbation simulations, the entropy variation of the trans–gauche conformational equilibrium of 1,2-dichloroethane in water has been computed. Thermodynamic cycles have been used to evaluate the contribution of the van der Waals, electrostatic and polarization forces. Although the experimental free energy is reproduced, the simultaneous reproduction of the experimental free energy and entropy thermodynamic quantities cannot be obtained. The scaling of the solute atomic charge and polarizability values is not able to improve the results. To get proper entropy values for this conformational equilibrium, a new reparametrization involving both solute and solvent molecules is required.
NH3(ν 2) inversion doubling and two-mode interaction of PH3(ν 4,ν 2) in V–V energy transfer with PH 2 ( X ˜ 2 B 1 ; v 2 ″ = 1 ) by Chieu Nguyen Xuan (415-419).
The collision induced deactivation constants of PH 2 ( X ˜ 2 B 1 ; v 2 ″ = 1 ) by H2S and NH3 have been determined. The NH3 constant appears to be anomalously high with respect to other polyatomic quenchers data in V–V energy transfer with PH 2 ( v 2 ″ = 1 ) . This deviation of the NH3 value has been ascribed to the inversion doubling of this molecule. The deactivation constant by PH3, determined in a previous work, has been re-examined. The removal of PH 2 ( v 2 ″ = 1 ) should be due to two PH3 vibrational modes, i.e., ν 2 and ν 4, and not to the single ν 4, as formerly assumed, and their respective contributions have been estimated.
Preparation and photophysical properties of nanostructured 9-cyanoanthracene by S.K. Pal; S.K. Batabyal; T. Ganguly (420-424).
This Letter reports a new method (refluxed) along with the conventional sonication method for preparation of nanoparticles of well-known electron acceptor 9-cyanoanthracene (9CNA). The photophysical properties of the nanostructured 9CNA, prepared from both the methods were investigated by steady-state and time resolved spectroscopic techniques. Nanoclusters, made from the refluxed method, are mostly one-dimensional wire-like structure whereas in the sonication method formations of both one and three-dimensional nanocluster of 9CNA were confirmed from TEM investigation. Irradiation of both the 9CNA nano dispersions results in formations of both the delocalized π-electronic (polaron–exciton) and the locally excited states.
Self-assembled methanofullerene vesicles and their encapsulation of pyrene by Junxin Li; Na Sun; Pu Zhang; Zhi-Xin Guo; Daoben Zhu (425-429).
Fullerene vesicles were fabricated from a neutral methanofullerene derivative with hydrophobic–hydrophobic–hydrophilic structure (TDC60). For the first time, a water-insoluble organic molecule of pyrene was encapsulated into the vesicles and resulted in novel organic core-shell suprastructure and the photophysical properties were researched systemically.
Ab initio study of the water adsorption on hydroxylated graphite surfaces by B. Collignon; P.N.M. Hoang; S. Picaud; J.C. Rayez (430-435).
In this work, we study the interaction between small water aggregates and hydroxylated graphite surfaces by means of quantum calculations. The hydroxylated graphite surfaces are modelled by anchoring OH groups on the face side or on the edges of a graphite crystallite of nanometer size. The quantum calculations based on the ONIOM approach aim at characterizing the adsorption properties (structure and adsorption energy) of small water aggregates containing up to five water molecules, in order to better understand at a molecular level the role of these OH sites on the hydrophilic properties of graphite surface modelling soot emitted by aircraft.
Spectroscopic properties of Pr3+: 1D2 → 1G4 transition in SiO2-based glasses by Yong Gyu Choi; Jung Hyun Baik; Jong Heo (436-440).
The Pr3+: 1D2 → 1G4 transition in silica-based oxide glasses, which emits a strong luminescence centered at about 1530 nm with full-width at half-maximum wider than 200 nm, may reserve potential practicality owing to its fairly long fluorescence lifetime of ∼270 μs corresponding to theoretical quantum efficiency approaching unity and its emission wavelengths matching up to the optical communication window of silica transmission fiber. To minimize non-radiative energy transfers among the active ions, the host materials need doping concentration of Pr2O3 tantamount to not more than 0.01 mol%. Impact of ground state absorption to (3F3, 3F4) level on the emission is discussed and then efficient excitation schemes are proposed.
Investigation of the CO + NO reaction over the Cu(0 0 1) surface by P.J. Godowski; J. Onsgaard; A. Ga¸gor; M. Kondys; Zhe Shen Li (441-445).
Coadsorption of NO + CO and CO + NO on Cu(0 0 1) at 115 K was investigated by valence band and core-level photoelectron spectroscopy based on the use of synchrotron radiation (SR-PS). Site exchange between NO and CO takes place when a CO saturated Cu(0 0 1) surface is exposed to NO. Both molecular and dissociated NO are observed on the surface. The effect of heating to 300 K was followed. The opposite adsorption sequence, CO exposure of the Cu(0 0 1) surface with preadsorbed NO, results in oxidation of CO and bonding of CO2. Heating to 300 K causes desorption of the adsorbed CO2, NO and N.
Theoretical study of the dehydrogenation reaction of ethane catalyzed by zeolites containing non-framework gallium species: The 3-step mechanism × the 1-step concerted mechanism by Marcio Soares Pereira; Marco Antonio Chaer Nascimento (446-451).
The dehydrogenation reaction of ethane in gallium containing zeolites was studied using density functional theory (DFT) and a non-framework gallium species in the dihydridegallium ion form. Two different mechanisms were considered when examining the dehydrogenation reaction of ethane: a 3-step mechanism and a 1-step concerted mechanism. The activation energy calculated for the concerted mechanism is greater than the one calculated for the 3-step mechanism. In spite of that, due to the major conformational changes involved in the 3-step mechanism, the concerted one could be favored once one considers the effects of the zeolite framework, mainly for larger substrates.
Dipolar field effects described by boson operators techniques: The case of intermolecular multiple-quantum coherences in liquids by W. Nosel; T. Gili; S. Capuani; B. Maraviglia (452-456).
Dipolar couplings between macroscopically distant spins in solution nuclear magnetic resonance (NMR) are treated. We propose a novel technique to calculate the intermolecular multiple-quantum coherences (iMQCs) based on a boson operators approach. The choice of an annihilation and creation operator basis set allows us to produce a general expression of the NMR signal depending on local inhomogeneities of magnetic field. The general expression we derive fits into the well known background of iMQCs signal descriptions [J. Jeener, J. Chem. Phys. 112 (2000) 5091] and turns into the conventional quantum-mechanical Warren formulation [S. Lee, W. Richter, S. Vathyam, W.S. Warren, J. Chem. Phys. 105 (1996) 874] by means of appropriate approximations.
Fractal dimension and photoluminescence of ZnO tetrapod nanowhiskers by Run Wu; Yingge Yang; Shanhai Cong; Zhanghan Wu; Changsheng Xie; Hiroyuki Usui; Kenji Kawaguchi; Naoto Koshizaki (457-461).
ZnO tetrapod nanowhiskers were prepared and characterized using fractal dimension analysis. The fractal dimension of well-developed ZnO nanowhiskers was higher than 1.7, while that of ZnO nanoparticles was lower than 1.6. In addition to UV band-edge emission, nanowhiskers of large fractal dimension having well-developed ZnO crystalline feet and a Zn phase at the tetrapod center exhibited two visible emissions at wavelengths of 419 and 438 nm at room temperature.
Three-photon absorption enhancement in symmetrical charge transfer pull–pull fluorene derivatives by Ion Cohanoschi; Kevin D. Belfield; Florencio E. Hernández (462-466).
We report the multiphoton-induced upconversion fluorescence of 2,7-bisbenzothiazole-9,9-didecylfluorene (Acceptor-π-Acceptor) in hexane solution, pumping at wavelengths from 300 to 1200 nm, and its three-photon absorption cross-section at 1095 nm ( σ 3 ′ = 355 × 10 - 78 cm 6 s 2 photon - 2 for the transition S0 → S1). The multiphoton-induced fluorescence emission and the absorption measurements of 2,7-bisbenzothiazole-9,9-didecylfluorene in hexane were performed with a tunable OPG pumped by a Nd-YAG picosecond laser. It is demonstrated that the strong symmetrical electron-transfer from the electron rich fluorene core to the two electron-withdrawing benzothiazole end groups enhances σ 3 ′ . An increase of approximately four and nine fold, with respect to its Donor-π-Donor and Acceptor-π-Donor counterparts, respectively, was observed.
Accuracy and sensitivity of determining molecular orientation at interfaces using sum frequency generation vibrational spectroscopy by Wei Gan; Bao-hua Wu; Hua Chen; Yuan Guo; Hong-fei Wang (467-473).
Polarization null angle (PNA) method is an accurate alternative to the commonly used polarization intensity ratio method in determination of molecular orientation at interfaces with sum frequency generation vibrational spectroscopy (SFG-VS). Here, the accuracy and sensitivity of PNA method is tested on different experimental configurations. It is found that its accuracy and sensitivity are more sensitive to the incident angle of the visible beam than the IR beam, and the range of the optimal experimental configurations is identified. This development makes better understanding of the polarization measurement in SFG-VS, and should find more applications for interface studies.
Orientation of nitrous oxide on palladium(1 1 0) by STM by Kazuo Watanabe; Anton Kokalj; Yoshiya Inokuchi; Izabela Rzeznicka; Keijiro Ohshimo; Nobuyuki Nishi; Tatsuo Matsushima (474-478).
The adsorption structure of N2O on Pd(1 1 0) was analyzed below 14 K by scanning-tunneling microscopy. The N2O monomer was oriented along the [0 0 1] direction in the on-top form. Furthermore, the formation of small aggregates extending along the [ 1 1 ¯ 0 ] direction was observed. The observed images were well-simulated for two types of cluster structures optimized by density-functional theory calculations. The components in the aggregates are proposed to be in a tilted form either on bridge sites or on-top sites.
Optical spectra of quantum dots: A non-adiabatic approach by T.O. Cheche; M.C. Chang (479-482).
The presence of accompanying resonances to the longitudinal optical phonon satellites in the optical spectra of semiconductor quantum dots is confirmed theoretically by a non-adiabatic approach of the optical absorption. The theory is applied to simulate features of the optical spectra of small spherical GaAs/AlAs quantum dots. The intensity and the spectral position of the accompanying resonances are influenced by both optically active and dark levels and increase to measurable values with temperature.
Ab initio quantum chemical study of electron transfer in carboranes by Ranjit Pati; Andrew C. Pineda; Ravindra Pandey; Shashi P. Karna (483-488).
The electron transfer (ET) properties of 10- and 12-vertex carboranes are investigated by the ab initio Hartree–Fock method within the Marcus-Hush (MH) two-state model and the Koopman theorem (KT) approach. The calculated value of the ET coupling matrix element, V AB, is consistently higher in the KT approach than in the MH two-state model. For the carborane molecules functionalized by –CH2 groups at C-vertices, V AB strongly depends on the relative orientation of the planes containing the terminal –CH2 groups. The predicted conformation dependence of V AB offers a molecular mechanism to control ET between two active centers in molecular systems.
The importance of tunneling effect to the decomposition of 2,2-dimethoxypropane and 2,2-diethoxypropane by Hui Jiang; Haoran Li; Tao Wu; Shijun Han (489-494).
The experimental results show that the decompositions of 2,2-dimethoxypropane (DMP) and 2,2-diethoxypropane (DEP) have nearly identical rate ratio of 2-methoxypropene (MPP) and 2-ethoxypropene (EPP) in ionic liquids. The yields ratio of MPP/methanol and EPP/ethanol were nearly 1.0. The four-center cyclic transition state was found in B3LYP density functional theory of level. Surprisingly, the experimental observations and theoretical rate constants ratio (k DEP/k DMP) appeared to differ about ten magnitudes at the experimental temperatures range. Further, dynamics study indicated that the significant tunneling effect played an important role in the identical rate constants ratio of the decomposition reactions at low temperatures range.
Air–liquid interface of ionic liquid + H2O binary system studied by surface tension measurement and sum-frequency generation spectroscopy by Jaeho Sung; Yoonnam Jeon; Doseok Kim; Takashi Iwahashi; Toshifumi Iimori; Kazuhiko Seki; Yukio Ouchi (495-500).
Surface of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) + water mixture is investigated using surface tension measurement and sum-frequency generation spectroscopy. The liquid surface is mostly covered by the [BMIM]+ cations at very low bulk concentration. An unusual increase in surface tension from mole fraction c ≈ 0.016 up to ≈0.05 suggested that the BF 4 - anions start to appear at the surface from c ≈ 0.016 until the anions and cations are equally populated at c ≈ 0.05 or higher. From the analysis of the spectra, the terminal methyl group of the butyl chain in the cation is polar-oriented with its symmetry axis aligning rather vertical to the surface for the whole range of concentration.
The magnitude of pseudo-potential errors for density functional calculations by Christian Janfelt; Frank Jensen (501-503).
It is shown that the use of pseudo-potentials for replacing the core electrons leads to errors in relative energies for density functional calculations which are comparable to the errors from using double or triple zeta type basis sets for systems composed of first- and second-row elements, respectively. The pseudo-potential error is ∼10 kJ/mol for relative energies, although errors in atomization energies are significantly larger.
Conformational properties of poly (vinyl Fluoride) based upon ab initio electronic structure calculations by Zhi-Jie Zhang; Zhong-Yuan Lu; Ze-Sheng Li; Chia-Chung Sun (504-508).
The geometries and conformational energies of model segments of poly (vinyl fluoride) (PVF) are obtained from quantum chemistry calculations and used to determine the statistical weight parameters in a rotational isomeric state (RIS) model. The interaction energies show that the electrostatic interaction is important in the molecules containing high electronegative atoms. The calculated characteristic ratio is in agreement with available theoretical values by means of molecular mechanics (MM).
π-electronic charge-transfer interactions in supramolecular complex formation between fullerenes and 5,10,15,20-tetrahexylporphyrin by Sumanta Bhattacharya; Naoki Komatsu; Manas Banerjee (509-518).
UV–Vis spectral investigations on fullerenes/5,10,15,20-tetrahexylporphyrin (TP) supramolecular complexes are reported in CCl4 and CHCl3. An absorption band due to charge transfer (CT) transition is observed in the visible region. Vertical ionization potential of TP was determined from the CT transition energy. CT is very weak in these complexes as reflected from very low values of oscillator strengths and transition dipole strengths. All of the complexes are found to be stable with 1:1 stoichiometry. Thermodynamic parameters for the supramolecular complexes of TP with - and fullerenes are reported. The high formation constant value for the fullerene/TP complex as compared to fullerene/TP complex indicates selectivity of TP molecule towards fullerene.
Author Index (519-526).