Chemical Physics Letters (v.387, #4-6)

Enzyme functionality and solvation of Subtilisin Carlsberg: from hours to femtoseconds by J.K.Amisha Kamal; Tianbing Xia; Samir Kumar Pal; Liang Zhao; Ahmed H Zewail (209-215).
We report studies of the enzymatic activity of Subtilisin Carlsberg (SC) in different solvents and pH's using two substrates. From the Michaelis–Menten mechanism, we found the specificity constant (k cat/K M) of enzymatic activity to be retarded when organic solvents, such as acetonitrile or dioxane, are added to the aqueous medium or when the pH is lowered. In order to address the role of solvation, we also studied the femtosecond dynamics of the enzyme and the solubility of substrates and products. We elucidate the nature of the free energy surface from the knowledge of the free energy change (K M), catalytic turn over (k cat), solvation, and effect of pH on the enzymatic activity.

Approximate cumulative reaction probabilities have been calculated from two empirical rate equations: one is the 3-parameter rate equation, AT n exp(−E/k B T), and the other is the modified Arrhenius equation, A exp(−E0/k B T2+T0 2 ) proposed in Chem. Phys. Lett. 160 (1989) 295, for expressing the rate constants at low temperatures. Numerical calculations were made for the D + H2  → DH + H reaction. It is shown that this reaction occurs mainly through tunneling at 200 K, and that the 3-parameter rate equation involves the tunneling effect along with the correction at high temperatures.

Caging enzyme function: α-chymotrypsin in reverse micelle by Ranjit Biswas; Samir Kumar Pal (221-226).
We report studies of the enzymatic activity of α-chymotrypsin (CHT) in aqueous buffer and AOT reverse micelle with various degrees of hydration using the substrate Ala–Ala–Phe–7-amido-4-methylcoumarin (AMC). From Michaelis–Menten kinetics, we determined equilibrium and rate constants for catalytic activity in aqueous buffer. In the reverse micelle we found that the activity of CHT to be retarded by two orders of magnitude compared to that in aqueous buffer. The activity is also found to be nearly insensitive to the degree of hydration of reverse micelle. From these studies, we attempt to elucidate the influence of hydration on enzyme activity.

Hybrid adaptive grid algorithm for wave packet propagation by Dmytro Babyuk; Robert E. Wyatt (227-232).
A three-stage hybrid adaptive algorithm is applied to wave packet scattering from a repulsive barrier. As the packet approaches the barrier during the first stage, quantum hydrodynamic equations (QHE) are integrated on a moving equally-spaced grid. In the second stage, when nodes form in the reflected wave packet, the wavefunction is integrated on a fixed grid while the transmitted part is still treated using the QHE. In the third stage, when ripples have replaced the nodes, the QHE are integrated separately for the reflected and transmitted components. The method is stable for long propagation times (1 ns).

Stability of high-energy nitrogen-rich sulfides S(N4) m by Li Jie Wang; Paul G. Mezey (233-237).
Ab initio calculations suggest that structures S(N4) m (m=1–3) correspond to local energy minima on the relevant potential energy surfaces. S(N4)3 is 5.8 kcal/mol lower in energy than the transition structure of dissociation, and sulfur atom prefers an sp3d2 hybridization. S(N4)2 and SN4 are somewhat more stable kinetically, due to 17.3 and 13.5 kcal/mol barriers of dissociation. The low gas phase barriers of S(N4) m mean that these nitrogen-rich sulfides require external stabilization if they are to be used as high-energy density materials. The special role of the sulfur d-orbitals in the geometrical arrangements of these systems was also investigated.

A QSPR study on optical limiting of organic compounds by Per Lind; Cesar Lopes; Kjell Öberg; Bertil Eliasson (238-242).
The optical limiting performance of 23 structurally different organic compounds has been measured at the wavelength of 532 nm. Molecular orbital ab initio calculations were performed to generate molecular electronic variables that were applied in a quantitative structure–property relationship (QSPR) study. A model that predicts the optical limiting response was constructed by using a partial least square (PLS) analysis. Six variables that play a major role for the optical limiting ability of organic materials were identified.

An HF/3-21G calculation was performed for crambin, which is present in seeds of Crambe abyssinica, at the recent 0.54 Å−1 resolution X-ray geometry. The resulting electron distribution function was analyzed using Bader’s topological method. The density at bond critical points in the peptide unit shows some scatter in the correlation with bond length. Additionally, (3,−3) critical points (local minima) were located in ∇ 2ρ( r ) within the valence shell charge concentration region of the carbonyl oxygen atoms. These points always lie near the plane of the peptide unit, which itself is sometimes not precisely planar.

Mechanical behavior of functionalized nanotubes by S. Namilae; N. Chandra; C. Shet (247-252).
The potential use of carbon nanotubes as reinforcements in composite materials is greatly enhanced by improving the fiber-matrix interface bonding. A proposed method to increase the fiber-matrix bonding is by functionalizing the nanotubes. We use molecular dynamics and statics simulations to study the tensile mechanical response of functionalized carbon nanotubes. It is found that the there is a marginal increase in stiffness in functionalized nanotubes, and the stiffness values are found to increase with the increase in number of attachments. When deformed at high temperatures, formation of topological and failure are found to occur at lower strains.

The first study of static polarizability and polarizability anisotropy of small iron clusters up to four atoms calculated in the framework of density functional theory is presented. The calculations were of all-electron type and performed using a finite field approach implemented in the density functional program AllChem. A newly developed first-order field induced iron basis set for density functional calculations was employed. The calculated polarizability of iron clusters shows that the size dependency of the static polarizability per atom of iron clusters follows the same trend as that observed for sodium and copper clusters.

Fluorescence from the second excited singlet state of 3-hydroxyflavone in supercritical CO2 by Nitin Chattopadhyay; Monica Barroso; Carlos Serpa; Luis G. Arnaut; Sebastião J. Formosinho (258-262).
Fluorescence from the second excited singlet state (S2) of 3-hydroxyflavone (3HF) has been observed for the first time in supercritical carbon dioxide (sc-CO2) environment. Steady-state experiments reveal that the intramolecular proton transfer is less effective from the S2 state of 3HF compared to that from the S1 state.

Photophysics of 3-hydroxyflavone in supercritical CO2: a probe to study the microenvironment of SCF by Nitin Chattopadhyay; Monica Barroso; Carlos Serpa; M. Isilda Silva; Luis G. Arnaut; Sebastião J. Formosinho (263-266).
The excitation of 3-hydroxyflavone (3HF) to its second excited singlet state (S2) gives rise to dual fluorescence in supercritical carbon dioxide. The ultraviolet fluorescence originated from the S2 state of 3HF is well separated from the green emission emanating from the tautomeric form, produced via the excited state intramolecular proton transfer. The relative intensity of the S2 to the tautomer fluorescence (S2/T) has been studied as a function of pressure and temperature. It is shown that this ratio reflects the microheterogeneity of the supercritical CO2, and confirms the value of fluorometric probes in disclosing the microscopic properties of supercritical fluids.

Thymine excision from DNA by subexcitation electrons by Hassan Abdoul-Carime; Sascha Gohlke; Esther Fischbach; Jessica Scheike; Eugen Illenberger (267-270).
We show the ability of slow electrons to effectively decompose gas phase thymidine into the sugar and thyminyl moiety, at comparable intensities. The reaction proceeds via dissociative electron attachment at energies below the threshold for electronic excitation (<3 eV), with the excess charge localized on the respective fragments. Within nucleic acid, this reaction may excise thymine from the DNA strands. Since ballistic low energy electrons are the predominant radiolytic species, the present findings represent an essential reaction in the understanding of the initial events in radiation damage of DNA.

Ab initio study of CNT NO2 gas sensor by Shu Peng; Kyeongjae Cho; Pengfei Qi; Hongjie Dai (271-276).
NO2 gas adsorption, diffusion, and reaction on a single walled carbon nanotube (SWNT) surface are studied using ab initio simulations. The small diffusion barriers of NO2 on SWNT surface suggest that NO2 molecules can produce NO and NO3 through chemical reactions. From the estimation of diffusion barriers and binding energies of NO2, NO, and NO3 on a SWNT surface, we show that NO3 is the most likely long-lived species on SWNT. This finding enables us to explain why the experimental recovery times of NO2 gas sensors have been measured to be as long as 12 h.

Complementing our recent work on subspace wavepacket propagation [Chem. Phys. Lett. 336 (2001) 149], we introduce a Lanczos-based implementation of the Faber polynomial quantum long-time propagator. The original version [J. Chem. Phys. 101 (1994) 10493] implicitly handles non-Hermitian Hamiltonians, that is, those perturbed by imaginary absorbing potentials to handle unwanted reflection effects. However, like many wavepacket propagation schemes, it encounters a bottleneck associated with dense matrix–vector multiplications. Our implementation seeks to reduce the quantity of such costly operations without sacrificing numerical accuracy. For some benchmark scattering problems, our approach compares favourably with the original.

Inhibition of one-electron oxidation of 1-pyrenesulfonate (PySA) included in cyclodextrins by sulfate radical anion (SO4 •−) occurred to give PySA radical cation (Py •+SA) with a peak at 455 nm during the pulse radiolysis of a mixture of PySA, potassium peroxodisulfate, and t-butanol. PySA is partly included in β-cyclodextrins (βCD) to form a PySA/βCD complex, while it exists only as a 2:2-inclusion complex, (PySA)2/(γCD)2 in γCD. The oxidation of PySA by SO4 •−was completely inhibited in βCD and γCD. This is explained by the shielding effect of CDs on the bimolecular collisional process of PySA and (PySA)2 in CDs with SO4 •−.

Multiplex integrated cavity output spectroscopy of cold PAH cations by Ludovic Biennier; Farid Salama; Manish Gupta; Anthony O'Keefe (287-294).
Multiplex Integrated Cavity Output Spectroscopy (MICOS) is a new cavity-enhanced absorption method that allows the use of broadband dye nanosecond pulsed laser sources and offers a sensitivity equivalent to CRDS. MICOS has been coupled to a pulsed discharge slit nozzle to measure the spectra of the cold naphthalene (C10H8 +), acenaphthene (C12H10 +) and pyrene (C16H10 +) cations in the gas phase. A femtosecond relaxation timescale is measured for the D5←D0  (0–0) transition of C16H10 +. Spectra recorded at high plasma energies also show evidence of fragmentation. The CH radical is observed and carbon nanoparticles are generated in the plasma.

A new NMR method is presented to measure selectively the self-diffusion coefficient of molecules with 13C–1H bonds. The method is based on the selection of spectral lines by both 13C chemical-shift and 13C–1H J-coupling encoding, which generally is adequate to individuate a molecular species. Although the approach has preferential utilization in bio-molecular systems, it may be employed when a direct or indirect chemical bond has chemical shift and J-coupling coordinates able to localize uniquely a certain molecular species. The method may also be utilized to attain self-diffusion weighted NMR imaging (MRI) of single molecular species. Here results on glucose metabolites in aqueous solutions are presented. The approach shows a chemical selectivity, which is higher than the traditional NMR stimulated echo approach.

Resonant Raman spectra of carbon nanotube bundles observed by perpendicularly polarized light by A. Grüneis; R. Saito; J. Jiang; Ge.G. Samsonidze; M.A. Pimenta; A. Jorio; A.G. Souza Filho; G. Dresselhaus; M.S. Dresselhaus (301-306).
We calculated the resonance condition for the radial breathing Raman mode for single wall carbon nanotube (SWNT) bundles for light polarization parallel and perpendicular to the tube axis. The radial breathing modes that are not observed in isolated SWNTs, but are observed in SWNT bundles, are assigned to a resonance process for light with perpendicular polarization. Asymmetry between the valence and conduction π energy bands becomes essential for obtaining resonance conditions. We find that due to a high joint density of states, armchair SWNTs have the largest optical transition intensities.

CFD prediction of carbon nanotube production rate in a CVD reactor by Hajime Endo; Kazunori Kuwana; Kozo Saito; Dali Qian; Rodney Andrews; Eric A. Grulke (307-311).
Chemical vapor deposition (CVD) is known as one of the most efficient methods of synthesizing carbon nanotubes. This Letter presents a computational fluid dynamics (CFD) model to predict the production rate of nanotubes via catalytic decomposition of xylene in a CVD reactor. In our model, two gas-phase reactions and four surface reactions were considered. The rate constants of the surface reactions were determined using the inverse technique based on the measured tail gas concentrations. The predicted production rate agreed well with the experimental data, validating our model.

Reactions of amide group with fluorine as revealed with surface analytics by Tihomir Solomun; Arnd Schimanski; Heinz Sturm; Eugen Illenberger (312-316).
Thin polyamide-6 films were exposed to fluorine gas and analysed with photoelectron and infrared spectroscopies. Fluorine cleaves the amide C–N bond resulting in the formation of the –COOH and –NF2 terminal groups. This is evident from large shifts in the N1s binding energy (+5 eV) and CO stretching frequency (∼80 cm−1), appearance of ester oxygen in the XPS spectra, as well as by the 19F nmr spectra of volatile products consistent with a terminal NF2 group.

A simple analytical expression for the current function pertaining to the irreversible electron transfer processes in linear sweep voltammetry is formulated for the systems obeying Marcus-like mechanisms. The influence of activation overpotential on the current function has been pointed out. The variation of the current function with solvent reorganization energy has also been illustrated which is in agreement with Marcus theory. The current function expression was verified experimentally using the reductive cleavage of carbon tetrachloride in N,N -dimethylformamide at glassy carbon electrodes.

The isotopic composition of dihydrogen generated from formaldehyde in highly basic solutions has been investigated. It is shown that two pathways are available for the reaction. In the first pathway, one hydrogen atom is aquated hydrogen and the other is methylene-hydrogen. In the second pathway both hydrogen atoms originate from the methylene moiety of the formaldehyde. When the source of dihydrogen is the corresponding reaction of glyoxylate, only the first pathway is observed. The changes of the Mulliken charges and the geometrical parameters in dependence on the number of H-bonded water molecules support the experimental finding that the probability of both hydrogen atoms originating from the methylene moiety of formaldehyde is higher.

An ESR study of dynamic biradicals of two TEMPOs bridged with –(SiMe2) n – (n=1–4) in liquid solution by Kenji Komaguchi; Toshiyuki Iida; Yumiko Goh; Joji Ohshita; Atsutaka Kunai; Masaru Shiotani (327-331).
Biradicals composed of two TEMPOs (2,2,6,6-tetramethylpiperidinol-oxyl) bridged with –(SiMe2) n – (n=1–4) to each other were synthesized and subjected to an ESR study. A quintet spectrum of an isotropic 14N-hyperfine splitting of 21.6 MHz (g=2.0070) was observed for biradical 1 (n=1) and a triplet of 43.3 MHz (g=2.0072) for biradical 4 (n=4) in 3-methylpentane at 190 K. The Si-linkage was found to effectively enhance the spin–spin exchange interaction compared with the corresponding carbon fragments. The reversible temperature dependence of the spectra was analyzed based on a model of a modulated spin exchange interaction due to a tumbling motion. The apparent activation energies for the intramolecular dynamics were found to be 5.1–10.6 kJ mol−1 in 3-methylpentane and 2-methyltetrahydrofuran solutions.

A model for the van der Waals bond by Valerio Magnasco (332-338).
A two-state model of van der Waals (VdW) interactions is presented which completes the elementary description of the interactions occurring between atoms and molecules. A weak VdW bond is formed between closed-shell atoms or molecules as soon as the small Pauli repulsion is offset in long range by attractive VdW interactions. These are distortion and dispersion interactions, related to the electric properties of the interacting molecules, and described as small second-order effects in terms of long range interaction integrals βs. The explicit forms of these βs are derived from classical electrostatics for atom–atom, atom–linear molecule dispersion, and atom–linear molecule induction. Comparison between C 6 dispersion and induction coefficients for simple homodimers shows that dispersion is, in general, the most important attractive VdW interaction in long range.

Two-photon spectroscopy of aligned acetaldehyde by Y. Kim; H. Meyer (339-344).
We reinvestigate the two-photon absorption of the (3s-n) transition in acetaldehyde and its implications for the observation of collision-induced alignment. The two-photon spectroscopy of an aligned ensemble of acetaldehyde produced in collisions with He provides clear evidence for the quantum interference of tensors of different rank. The observed polarization effect can be understood in terms of the non-vanishing tensor components Z 0 (0)=1.0, Z 0 (2)=0.4±0.1 and |Z ±2 (2)|=0.3±0.1. For a collision energy of 916 cm−1, the alignment is largely consistent with the predictions of the kinematic apse model.

Change of molecular packing and orientation from monolayer to multilayers of hydrogenated and fluorinated carboxylates studied by in-plane X-ray diffraction together with NEXAFS spectroscopy at C K-edge by Atsuhiro Fujimori; Yoshiko Sugita; Hiroo Nakahara; Eisuke Ito; Masahiko Hara; Noritaka Matsuie; Kaname Kanai; Yukio Ouchi; Kazuhiko Seki (345-351).
By applying the in-plane X-ray diffraction together with the NEXAFS spectroscopy to organized molecular films, the molecular orientation and packing from the monomolecular layers to multilayers of hydrogenated and fluorinated long-chain carboxylic acids and carboxylates were characterized. The two-dimensional molecular packing in the monolayers for cadmium salts of fatty acids was clearly different from those for fatty acids as well as those in the multilayers, whereas the fluorinated long-chain carboxylates had hexagonal packing of the rod like molecules common in both mono- and multilayers. This seems to be probably due to difference of molecular cohesive energy between hydrocarbons and fluorocarbons themselves.

Time-dependent DFT (TD-DFT), CIS, and CASSCF calculations of the excited singlet states of diphenylacetylene demonstrate the existence of a low energy crossing between the initially excited ππ state (1 1B1u in D2h) and the dark πσ state (1 1Au in C2h). The state switch from the linear ππ state to the bent πσ state accounts for all the unusual photophysical and spectroscopic properties of DPA, including an abrupt fluorescence break-off, and the appearance of the temperature/viscosity dependent transient absorption at 700 nm. The calculations also yield the ππ /πσ intersection for phenylacetylene and benzonitrile, suggesting that the state switch may be a phenomenon of common occurrence in aromatic molecules containing CC and CN groups.

Role of defects on the gas sensing properties of carbon nanotubes thin films: experiment and theory by L. Valentini; F. Mercuri; I. Armentano; C. Cantalini; S. Picozzi; L. Lozzi; S. Santucci; A. Sgamellotti; J.M. Kenny (356-361).

Spectroscopic studies of proton transfer in hydrogen bonding: adenine complexed to HCl by A. Dkhissi; L. Houben; L. Adamowicz; G. Maes (362-366).
The H-bond interaction of the adenine with HCl is investigated using the combined matrix-isolation FT-IR and theoretical density functional theory. Theoretical calculations indicate that three closed complexes of the type III (proton transfer or ion pair H-bond), each containing two hydrogen bond, i.e., N1 +–H⋯Cl⋯H–NH; N3 +–H⋯Cl⋯H–N9 and N7 +–H⋯Cl⋯H–NH, have been obtained. The experimental spectra are consistent with this prediction.

The angular pattern of scattered X-ray radiation (1.2–2.5 Å) from flames has been measured and analyzed. The results are compared with calculations on different molecules, such as polyaromatic hydrocarbons, fullerenes and other spherical structures. Measurements have also been performed on soot condensed on a cooling plate inserted inside a flame. Size- and shape-dependent structures are observed in the measured patterns from flames as well as soot measurements. The agreement between calculations and measurements allow the determination of characteristic sizes of the different structures. We have identified aromatic and graphitic structures and features related to sub-nanometer spherical structures.

Nanoscale array of inversely biased molecular rectifiers by F. Jäckel; Z. Wang; M.D. Watson; K. Müllen; J.P. Rabe (372-376).
We report a scanning tunneling microscopy (STM) and spectroscopy (STS) study of an electron donor (hexa-peri-hexabenzocoronene, HBC) covalently linked to six electron acceptors (anthraquinone, AQ) in self-assembled monolayers at the graphite–liquid-interface. The HBCs and AQs order in two-component nanoscale arrays with distinctly different electronic properties of their elements as reflected by the relative STM contrast depending on the sample bias. STS reveals an inverse rectifying behavior of the two moieties within the tunneling junction, which is attributed to resonantly enhanced tunneling through the HOMO of the HBC and the LUMO of the AQ.

Inhibition effects of ethanol on the kinetics of glucose metabolism by S. cerevisiae: NMR and modelling study by Maso Ricci; Silvia Martini; Claudia Bonechi; Lorenza Trabalzini; Annalisa Santucci; Claudio Rossi (377-382).
Saccharomyces cerevisiae is an important model to understand the eukaryotic cells control mechanisms. In this Letter, an approach based on in vivo 13C NMR and mathematical modelling was presented to develop a basis for a deeper understanding of eukaryotic responses to environmental stresses. Despite the few metabolites included, the model describes correctly the dynamical behaviour of glucose degradation and ethanol production, providing a qualitative and quantitative description of the response of S. cerevisiae metabolism to stressful concentrations of ethanol. The data and the model highlight that an exogenous stress is able to influence the cellular activity and the ethanol production rate constant.

An intracellular calcium oscillations model subject to external colored noise is investigated. Internal signal stochastic resonance (ISSR) can be induced and significantly influenced by colored noise. The signal-to-noise ratio (SNR) exhibits two maxima with the increment of the correlation time as the noise intensity is fixed, indicating the occurrence of stochastic bi-resonance. Additionally, we find ISSR and explicit internal signal stochastic resonance (EISSR) have quite similar responses to colored noise, which implies there are some commonalities in their mechanisms.

We present an embedding scheme to introduce local corrections at post Hartree–Fock level to density functional theory (DFT) calculations. As a first application we study proton jump reactions in the zeolite HSSZ-13 and show that energy barriers and rate constants are significantly changed by second-order Møller–Plesset perturbation theory (MP2) corrections to plane wave based DFT calculations. Electronic energy barriers increase from 68 to 81 kJ/mol (dry zeolite), and from 22 to 30 kJ/mol (hydrated zeolite). The predicted heats of adsorption of one water molecule onto the Brønsted acidic sites O1 and O2 are 73 and 69 kJ/mol, respectively.

In order to theoretically study on the magnetic coupling interaction in the Mn–Mn dimer, quantum chemical calculations on the equilibrium Mn–Mn distance R e, total energy E T, binding energies B e and exchange interaction energies E(S) under different spin multiplets were performed at CASPT2 level of theory. It is found that the calculated R e, E T, and B e values are correlated with the spin multiplet, and with increasing the total spin S, R e increases, but E T and B e exhibit a decrease trend. The exchange interaction energies E(S) deviate significantly from the `Lande interval rule'. This unusual magnetic phenomenon is primarily attributed to the biquadratic j(S a ·S b )2 term contribution in spin Hamiltonian for the Mn–Mn dimer.

Nano-particulate CuI film formed on porous copper substrate by iodination by Yang Yang; Xuefei Li; Bin Zhao; Huilan Chen; Ximao Bao (400-404).
A nano-particulate thin CuI film is fabricated by iodination of a porous copper substrate that was prepared by using an alumina mask and characteristic properties of these films are studied.

Some dynamical properties of nitrogen-14 quadrupolar spin-system with non-symmetric electric field gradient tensor by T.N. Rudakov; V.T. Mikhaltsevitch; P.A. Hayes; W.P. Chisholm (405-409).
The behaviour of nuclear quadrupole resonance (NQR) signal was studied in the `observation windows' between RF pulses after applying a multi-pulse sequence to a nitrogen-14 spin-system with a non-symmetric electric field gradient tensor using a phase-cycling technique. The experiments revealed some peculiarities in the behaviour of the signals which are important for the understanding of the dynamic properties of the quadrupolar spin-system.

Ab initio studies of MHe n +(M=Be, Mg; n=1–4) complexes by Xinping Bu; Chongli Zhong; A.F Jalbout (410-414).
The MHe n +(M=Be, Mg) complexes with n=1–4 were investigated by ab initio calculations at the levels of HF, MP2 and MP2(full)/6-311+G(3df, 3pd). The complexes were found to be stable, and the calculated results show that the C3V geometry is stable for the MHe3 + complexes, and the C2V geometry is stable for the MHe4 + complexes.

For the analysis of the spin-dipole (SD) term of the indirect NMR spin–spin coupling constant, the SD spin-polarization distribution and the SD energy density distribution are derived and used to explain magnitude and sign of the SD term. Orbital pairs (occupied, virtual) are identified that are most important for the SD spin–spin coupling mechanism. The induction of strong SD spin-polarization requires low excitation energies and complementing nodal properties of zeroth and first-order orbitals. The SD components for 1 J(CC) of typical CC bonds are analyzed. The SD term is a sensitive antenna for detecting the π-character of a bond.

MP2/cc-pVXZ and MP2/aug-cc-pVXZ (X=D, T, Q) complete basis set extrapolation calculations were carried out on the four minimum energy structures located on the potential energy surface of the OCS   (HCCH)2 van der Waals complex. The trimer structure consists of an averaged structure representing the dynamical interconversion between two equivalent forms with the (HCCH)2 face adopting a T-shaped conformation. The transition structure is a energetically close-lying geometry with a near-parallel disposition of the two HCCH fragments.

Positronium inhibition in naphthalene at high pressures by Tomasz Goworek; Jan Wawryszczuk; Radoslaw Zaleski (433-435).
The lifetime of ortho-positronium in solid naphthalene shortens with the rise of pressure as a result of diminishing the free spaces in which it is trapped. At the pressure ≈100 MPa the size of these spaces is too small to accommodate the Ps atom (no energy level in the well), and the intensity of ortho-Ps component, initially weakly dependent on pressure, abruptly drops to zero. The narrow range in which ortho-Ps disappears indicates uniformity of Ps-accommodating voids. The nonmonotonous dependence of free positron lifetime is discussed in the framework of the blob model.

High spectral resolution multiplex CARS spectroscopy using chirped pulses by K.P. Knutsen; J.C. Johnson; A.E. Miller; P.B. Petersen; R.J. Saykally (436-441).
A simple technique for achieving high spectral resolution coherent anti-Stokes Raman scattering (CARS) spectra with a femtosecond laser system is presented. A linearly chirped and stretched (∼10 ps) pump pulse generates CARS signal only when overlapped in time with the Stokes pulse (90 fs), creating a `temporal slit' that defines the spectral resolution of the technique. Multiplex CARS spectra for liquid methanol and liquid isooctane are presented, demonstrating a spectral resolution of better than 5 cm−1. This new chirped (c-CARS) technique should prove useful for chemically-selective imaging applications, as it significantly reduces the non-resonant background contribution.

Extended coupled-cluster approach for magnetizabilities of small molecules by Prashant Uday Manohar; Nayana Vaval; Sourav Pal (442-447).
Extended coupled-cluster method has emerged as a compact method for study of energies and electric properties of molecules and extended systems. In this Letter, we present a linear response to the above method for study of magnetizabilities of small test molecules. Specifically, we have presented results of diamagnetic and paramagnetic magnetizabilities of HF and CO in appropriate basis sets and studied the gauge dependence and basis set dependence of the properties evaluated through the above method. The results have been compared with SCF and NCC values, as well as experimental values.

A novel mechanism of charge separation in a dimer of two-orbital molecular system is proposed. The effective electron–electron repulsive energy in the dimer, U eff, has been estimated by means of valence-bond (VB) model calculations for the ground state of the dimer. It has been found that the HOMO–LUMO interplay leads to negative U eff in the strong dimerization condition, indicating spontaneous separation of charges on dimers (2 dimer  → dimer0  + dimer2−). Possible relevance to experimental features in some [Pd(dmit)2] salts (dmit=1,3-dithiol-2-thione-4,5-dithiolate) is discussed.

The structural, electronic and vibrational properties of LiOH and NaOH: an ab initio study by Mohammadou Mérawa; Pierre Labeguerie; Piero Ugliengo; Klaus Doll; Roberto Dovesi (453-459).
The structural equilibrium parameters, the formation and hydration energies, and the O–H vibrational frequencies of LiOH and NaOH have been investigated at the ab initio level by using the periodic Crystal package. Four different methods have been adopted for comparison. The computed structural parameters are in good agreement with experiment. Computational results are all in excellent agreement with experiment, except for the heat of hydration of LiOH, which was found to be overestimated with respect to experiment. The OH group in the two cases does not present any hydrogen bond type interaction. Among the four methods, B3LYP gives the best results for all the features considered, in particular for the OH(D) vibrational data.

In order to analyze the fluctuation of proteins, which plays an important role for folding structure and stability, an ab initio MO-MD program (FMO-HA) based on the fragment MO method has been developed and examined its efficiency in comparison with conventional RHF MO-MD. FMO gives the same potential of dissociation energy between fragments as well as RHF. FMO-HA and RHF MO-MD calculations show similar trajectories and geometrical changes. Furthermore, FMO-HA simulation enables us to elucidate the interaction energy between fragments accompanying with the dynamics. FMO-HA method is an efficient tool to determine the driving force of fluctuation of proteins.

Indium-doped zinc oxide nanobelts by Jiansheng Jie; Guanzhong Wang; Xinhai Han; Qingxuan Yu; Yuan Liao; Gongpu Li; J.G. Hou (466-470).
In-doped ZnO nanobelts were fabricated by thermal evaporation with assistance of gold catalyst. The nanobelts have high crystal quality and grow along [10 1 ̄ 0] direction with (0 0 0 1) dominated surface, and have an average In:Zn value of 1:30. A growth mechanism based on VLS is proposed to understand the nanobelts growth, explaining Au particles are only found at the ends of short narrow part of the nanobelts that are mostly uniform broad flat. The ZnO UV emission peak redshifting about 200 meV after doping gives an estimate of the carrier density in the doped ZnO nanobelts can be as high as 7 × 1019 cm−3.

We have constructed a small ferroin-catalyzed Belousov–Zhabotinsky reactor connected with a main reactor through continuous mass flow. When each reactor is in an independent oscillating state, the activation energy of the oscillation frequency differs considerably from each other, which enables us to investigate the oscillating state of the former under precise control of the latter through coupling strength and frequency difference. With increasing flow rate, both synchronized and intermittent oscillations appear according to the sign of the frequency difference. A precursor exists near the synchronization, while the transition from resting to oscillating state takes place in a timely manner for the intermittent oscillation.

Stability of As n [n=4, 8, 20, 28, 32, 36, 60] cage structures by Tunna Baruah; Mark R. Pederson; Rajendra R. Zope; M.R. Beltrán (476-480).
We present all-electron density functional study of the geometry, electronic structure, vibrational modes, polarizabilities as well as the infrared and Raman spectra of fullerene-like arsenic cages. The stability of As n cages for sizes 4, 8, 20, 28, 32, 36, and 60 wherein each As atom is threefold coordinated is examined. We find that all the cages studied are vibrationally stable and while all the clusters are energetically stable with respect to isolated arsenic atoms, only As20 is energetically stable against dissociation into As4. We suggest that the Raman spectra might be a means for observing the As20 molecule in gas phase.

About the topological classification of the metal–metal bond by Giuliana Gervasio; Riccardo Bianchi; Domenica Marabello (481-484).
Metal–metal bonds belong, from the topological point of view, to the wide class of the closed shell interactions proposed by Bader. Such a simple classification is, however, not satisfying in the description of these bonds and the nature of the metal–metal bond, in particular in polynuclear complexes, is debated. Using some topological and energy parameters, a comparison is made between polynuclear complexes and bulk metals and indicates the similar nature of these bonds.

In the iterative solution of the contracted Schrödinger equation (CSE) the 3- and 4-particle reduced density matrices (RDMs) are reconstructed from the 2-RDM via cumulant expansions. Under 1-particle unitary transformations, we establish that the connected (or cumulant) part of an RDM maps onto the connected part of the RDM in the transformed basis set. Consequently, neglecting the connected RDM in the CSE produces an error which is invariant under unitary transformations of the one-particle basis set. We illustrate this result with calculations on beryllium. The present results are applicable to unitary localization in linear-scaling RDM calculations for large molecules.

Aligned terrylene molecules in a spin-coated ultrathin crystalline film of p-terphenyl by R.J. Pfab; J. Zimmermann; C. Hettich; I. Gerhardt; A. Renn; V. Sandoghdar (490-495).
We report on the use of a simple spin casting procedure to fabricate very thin crystalline films of p-terphenyl doped with fluorescent terrylene molecules. By performing single molecule studies, we show that the guest molecules are oriented normal to the plane of the film. We find that despite the very low thickness of the p-terphenyl matrix, as thin as only 20 molecular layers, about half of the embedded emitters withstand photobleaching for illumination times of at least a day.

Highly efficient and stable doped hybrid organic–inorganic materials for solid-state dye lasers by Angel Costela; Inmaculada Garcı&#x0301;a-Moreno; Clara Gómez; Olga Garcı&#x0301;a; Leoncio Garrido; Roberto Sastre (496-501).
Significant enhancement on the laser action of Rhodamine 6G (Rh6G) has been obtained for solid-state dye lasers based on hybrid matrices obtained by simultaneous polymerisation of 2-hydroxyethyl methacrylate with different weight proportions of tetraethoxysilane or tetramethoxysilane. Lasing efficiencies of up 28% and high stabilities, with no sign of degradation, albeit with some oscillations, in the initial laser output after 100 000 pump pulses at 10 Hz were demonstrated when pumping the samples transversely at 532 nm with 5.5 mJ/pulse. This photostability is, to the best of our knowledge, the highest achieved to date for organic, inorganic and hybrid matrices doped with Rh6G.

Self-assembled monolayers made of thiolated conjugated wires attached on gold surfaces currently attract a considerable interest in the field of nanoelectronics. The interactions taking place at the metal/molecule interface govern the electronic structure of the complex, and hence the barriers for charge injection from the electrodes to the molecules. Considering benzenethiol as a prototype molecule, we investigate here the way the electronic structure is affected by the nature of the anchoring site of the sulfur atom on the gold surface and by the relative orientation of the molecule with respect to the surface. We also assess whether the changes in the molecular electronic properties upon substitution are similar for the isolated molecule and for the molecule attached on the gold surface. Our results provide strong evidences that, in order to introduce functionalities and/or improve charge injection in molecular devices, the electronic properties of conjugated molecular wires can be tailored by derivatization independently of the metal electrodes.

Time dependent DFT investigation on the two lowest 1Bu states of the trans isomer of stilbene and stiff-stilbenes by Roberto Improta; Fabrizio Santoro; Christian Dietl; Evangelos Papastathopoulos; Gustav Gerber (509-516).
We investigate at TD-DFT/PBE0/6-31+G(d,p) level of theory, the two lowest Bu states of the trans isomer of stilbene and two stiff-stilbenes, whose phenyl rings are blocked in the molecular plane by alkylic bridges, and whose two first Bu bands have been observed. At the Franck–Condon point, computations have been performed both in gas and in condensed phase by PCM method, and the results for the two stiff-stilbenes are in very good agreement with the experiments, predicting a strongly absorbing Bu state with a main HOMO → LUMO character and, about 0.6–0.7 eV higher in energy, a second weak absorbing Bu state, combination of the two HOMO → LUMO + 1 and HOMO-1 → LUMO excitations. A very similar picture is predicted for trans-stilbene in agreement with the experimental data and estimate. The dependence of the vertical excitation energies on the C–C ethylenic bond-distances and on the rotation of the phenyl rings has been explored for trans-stilbene in gas phase.

Author index (518-526).