Chemical Physics Letters (v.390, #1-3)

A robust pulse sequence for the determination of small homonuclear dipolar couplings in magic-angle spinning NMR by Per Eugen Kristiansen; Marina Carravetta; Wai Cheu Lai; Malcolm H. Levitt (1-7).
We present a new solid-state NMR pulse sequence that accomplishes efficient broad-band dipolar recoupling in systems with small dipolar couplings and large chemical shift anisotropies. The method involves a supercycled symmetry-based recoupling sequence incorporated in a constant-interval data acquisition strategy. The supercycle removes destructive higher-order average Hamiltonian terms, and makes the method more robust at long time intervals. We demonstrate 38.4% double-quantum filtering efficiency on diammonium [1,4-13C2]-fumarate in which the internuclear distance, as estimated by X-ray diffraction, is 387.8 pm. The estimated 13C–13C dipolar coupling was −136.5 ± 5.1 Hz, corresponding to an internuclear distance of 382.5 ± 4 pm.

The general failure of Kleinman symmetry in practical nonlinear optical applications by Christopher A. Dailey; Brian J. Burke; Garth J. Simpson (8-13).
Evidence is presented to refute the general applicability of the overall permutation symmetry condition originally proposed by Kleinman in describing the non-resonant nonlinear optical properties of the overwhelming majority of practical materials and systems. Kramers–Kronig dispersion relations demonstrate that the range of validity of Kleinman symmetry is substantially more restrictive than is widely assumed. These findings are supported by numerous experimental observations of effects explicitly forbidden by Kleinman symmetry but allowed by the dispersion relations. Considerations of molecular symmetry coupled with the Kramers–Kronig dispersion relations yield alternative simple and general macroscopic symmetry relations that are consistent with experimental observations.

Adsorption isotherms obtained by Smit et al. using Monte-Carlo simulation for alkane molecule adsorption in the narrow-bore nanotubular pores of Aluminophosphates show a highly unusual structure with chain length dependent steps and whose interpretation is uncertain. An exact calculation of the statistical mechanics of a lattice model of alkane molecule adsorption shows that the isotherm structure arises from the energetic cost of packing molecules into pores and is not directly related to capillary condensation. Three-dimensional interactions are not required to produce the isotherm steps.

Using terahertz pulsed spectroscopy to study crystallinity of pharmaceutical materials by Clare J. Strachan; Thomas Rades; David A. Newnham; Keith C. Gordon; Michael Pepper; Philip F. Taday (20-24).
The application of terahertz pulsed spectroscopy to polymorphic, liquid crystalline and amorphous forms of pharmaceutical compounds has been investigated. The different polymorphic forms of carbamazepine and enalapril maleate exhibit distinct terahertz absorbance spectra. In contrast to crystalline indomethacin and fenoprofen calcium, amorphous indomethacin and liquid crystalline fenoprofen calcium show no absorption modes, which is likely to be due to a lack of order. These findings suggest that the modes observed are due to crystalline phonon and possibly hydrogen-bonding vibrations. The large spectral differences between different forms of the compounds studied is evidence that terahertz pulsed spectroscopy is well-suited to distinguishing crystallinity differences in pharmaceutical compounds.

Magneto-dynamics of chiral carbon nanotubes by V. Krstić; G. Wagnière; G.L.J.A. Rikken (25-28).
Carbon nanotubes exist in achiral and chiral forms. The chiral nanotubes exist as two enantiomers which are each others' mirror image. By means of symmetry arguments it can be shown that a magnetic field imparts a linear momentum to the chiral nanotube. Inversely, a moving chiral nanotube generates a magnetic field. In order to quantify the first effect, the chiral nanotube is approximated by the quantum mechanical model of a free electron on a helix.

New data on the high resolution spectra of vibronic bands of the aniline–neon van der Waals complex with excess vibrational energy up to 1000 cm−1 above the S1 origin have been obtained. The rotationally resolved structure of the 121 0 and 6a2 0 bands of both 20Ne–aniline and 22Ne–aniline isotopomers reveal: (1) a dynamical contribution to the linewidth of the molecular eigenstates, (2) the existence of an accidental perturbation responsible for a local increase of the relaxation rate. The results are interpreted in terms of the competition between intramolecular vibrational redistribution and direct vibrational pre-dissociation processes.

Dynamics of a highly branched lipid bilayer: a molecular dynamics study by Wataru Shinoda; Masuhiro Mikami; Teruhiko Baba; Masakatsu Hato (35-40).
A comparison of branch-chained diphytanoylphosphatidylcholine (DPhPC) and straight-chained dipalmitoylphosphatidylcholine (DPPC) for their dynamics in the bilayers is made using 10 ns molecular dynamics simulations in the microcanonical ensemble. It is demonstrated that DPhPC molecules, compared with DPPC, indeed have slower wobbling, rotational, and translational motions by a factor of 2–3, whereas slightly faster headgroup rotation. The revision of the lipid dynamics due to chain branching is similar to that observed by the addition of cholesterol.

Two-photon spectroscopic properties of a new chlorin derivative photosensitizer by P.D. Zhao; P. Chen; G.Q. Tang; G.L. Zhang; W.J. Chen (41-44).
We report on the two-photon-excited (TPE) fluorescence spectrum and lifetime of a new chlorin derivative photosensitizer (CDP) in 0.9% NaCl solution with femtosecond laser pulses at 800 nm. The TPE fluorescence spectrum is similar to that obtained by one-photon excitation (OPE). The lifetimes of TPE and OPE fluorescence of CDP are of the order of 4.7 and 5.0 ns, respectively. The two-photon absorption (TPA) cross-section is σ 2 ≈33.6×10−50 cm4 s photon−1 at 800 nm. Our results indicate that the TPE and OPE photodynamic processes of CDP are basically similar. The lifetime and TPA cross-section suggest CDP may be a potential agent for two photon fluorescent microscopy and imaging as well as a photosensitizer in photodynamic therapy.

Ultrafast excitation relaxation dynamics and energy transfer in the siphonaxanthin-containing green alga Codium fragile by Seiji Akimoto; Iwao Yamazaki; Akio Murakami; Shinichi Takaichi; Mamoru Mimuro (45-49).
Ultrafast excitation relaxation dynamics and energy transfer processes in the siphonaxanthin (Siph)-containing green alga, Codium fragile, were examined using femtosecond time-resolved fluorescence spectroscopy. Fluorescence anisotropy decay and fluorescence lifetimes clearly indicated that an efficient Siph-to-chlorophyll (Chl) a energy transfer was achieved via the S1 state of Siph with a time constant of 400 fs. Energy migration times among Chl molecules were also resolved. Siph in the chloroplasts exhibited a new absorption band at approximately 535 nm, and we proposed that this originated from a new excited state (S x ) between the S2 and S1 states based on fluorescence anisotropy decay.

Photoionization of NO(A 2 Σ + , v=0,N) at 226 nm: ion-recoil momentum spectroscopy by Alexei I. Chichinin; Tina S. Einfeld; Christof Maul; Karl-Heinz Gericke (50-54).
We report the first observation of ion recoil induced by the ionization process for a molecule. The applicability of the method has been demonstrated by determining the β 2 and β 4 anisotropy parameters of the angular distributions of NO+ ions in the resonance-enhanced two-photon ionization of NO(X 2 Π 1/2 , v=0,J) via the A 2 Σ + (v *=0, N *) state at 226 nm. An energy resolution in the range of 10 μeV is demonstrated. The method might prove to be particularly useful for studying complex ionization-fragmentation processes as they occur for example for superexcited molecules.

It is observed that Fe3O4 nanoparticles exhibit a Verwey transition at approximately 120 K, in agreement with that observed in the corresponding bulk sample. While, the transition vanishes in the Fe3O4 nanoparticles formed under a 0.25 T magnetic field. It is found that the magnetic field induced oxidation of part of the Fe2+ ions on octahedral sites from lower spin states to higher spin states (Fe3+) during the formation of the nanoparticles, and then resulted in the vanishing of charge ordering between Fe2+ and Fe3+ on the octahedral sites below Verwey transition temperature (T V) due to lacking of Fe2+ in some layers.

A new approach is proposed to provide ultimate answers to such problem as the affinity difference between individual α- and β-subunits in different conformational forms of tetrameric hemoglobin. The approach is based on determination of the bimolecular association rate constant for O2 rebinding and the apparent quantum yield of photodissociation from single flash photolysis experiment. The potential of the approach is demonstrated with α- and β-subunits within human hemoglobin in the R-state.

Mass analyzed threshold ionization spectroscopy of p-fluorophenol cation and the p-fluoro substitution effect by Bing Zhang; Changyong Li; Huawei Su; Jung Lee Lin; Wen Bih Tzeng (65-70).
The origin of the S1  ← S0 electronic transition and the adiabatic ionization energy of p-fluorophenol are determined to be 35 117 ± 2 and 68 577 ± 5 cm−1, which are lower than those of phenol by 1232 and 48 cm−1, respectively. Most of the active vibrations in the electronic excited S1 and cationic ground D0 states are related to the in-plane ring modes. The p-fluoro substitution not only causes red shifts in the transition energies but also leads to a decrease in the frequencies of the observed vibrations. The present experimental findings are well supported by our ab initio and density functional calculations.

A density functional theory study applied for carbon isotope effects in the non-aqueous [Cu(CO)]+/CO system by Yuriko Ono; Yasuhiko Fujii; Shigeru Nagase; Takanobu Ishida (71-78).
DFT calculations were performed on the carbon isotopomers of CO and CO-complexes [Cu(NH2CH2CH2OH)3(CO)]+, [Cu(CH3OH)3(CO)]+ and results compared with (Du's) experimental results on the carbon isotope exchange equilibria between CO and CO–copper-complex. The gas-phase model was used even for calculating the isotope effects involving the solutes of solutions. Contributions of the extramolecular motion of the solute molecular to the RPFR are responsible for the steep slope of the lnα-vs. −1/T plot of Du's data, where α is the isotope separation factor which is identical to K in the present exchange system. The calculated result agrees well with (Du's) experiment data.

Identification of tetrahedrally ordered Si–O–Al environments in molecular sieves by {27Al}–29Si REAPDOR NMR by S. Ganapathy; Rajiv Kumar; V. Montouillout; C. Fernandez; J.P. Amoureux (79-83).
The silicon sites tetrahedrally connected to aluminum in framework positions of a molecular sieve may be identified by a selective reintroduction of the hetero-nuclear 27Al–29Si dipolar interaction through Rotational Echo Adiabatic Passage DOuble Resonance (REAPDOR) NMR. In this rotor synchronized 29Si MAS experiment, an effective dipolar dephasing of the Si–O–Al, over Si–O–Si, environments is shown to aid in the identification of silicon sites in the immediate vicinity of aluminum. Application of the method in the structurally interesting and novel molecular sieve ETAS-10 provides valuable insights on the details of aluminum substitution in the zeolite lattice and further leads to the first direct NMR estimate of Al–Si distance (r Al–Si=323±5 pm) in ETAS-10.

Study on optimization of molecular structure using Hamiltonian algorithm by Kazushige Ohtawara; Hiroyuki Teramae (84-88).
We apply the Hamiltonian algorithm combined with ab initio molecular orbital calculation to the optimization of molecular structure. The 6000 iterative calculations at Hartree–Fock 6-31G** levels shows that the HCN structure can be obtained even starting from the optimized structure of the HNC molecule, which cannot be achieved by conventional optimization methods, such as the Newton–Raphson method. The initial kinetic energies of less than 0.05 hartree and greater than 0.5 hartree fail in the optimization. The incorporation of a mixing term in the momentum space can accelerate the optimization.

High-intensity and ground-state influence on photoassociation line shapes of 88Sr by E.M.S. Ribeiro; A.L.M. Zanelatto; R.d.J. Napolitano (89-93).
The photoassociation probabilities of a sample of ultracold strontium atoms at 1 μK, are analyzed under the systematically varied conditions of frequency detuning and laser intensities, and for different dispersion values of the ground state potential curve. At low intensities, different values of dispersion coefficient of the ground state potential can give the same line shape, but at high enough intensity this multiplicity is lifted and the revealed periodic behavior is broken. The intensity of the laser becomes a control knob in the laboratory and it can be used to make better determinations of the ground state potential energy curve.

When molecules meet: a femtosecond study of the protonation of a base by Søren Rud Keiding; Dorte Madsen; Jane Larsen; Svend Knak Jensen; Jan Thøgersen (94-97).
The femtosecond dynamics of bi-molecular reactions is difficult to study as a common starting point for the reacting molecules cannot be established. However, by photochemical conversion of an un-reactive molecule into a reactive molecule, we can effectively mix two equilibrium solutions of reactive molecules on a picosecond timescale and follow the subsequent evolution of the bi-molecular reaction with femtosecond time resolution. We study the protonation of a base (peroxynitrite) and are able to separate the diffusive encounters of the two reacting molecules from the on-contact reaction probability for protonation of the base.

Electro-optic characterization of two novel organic materials in thin polymeric films by D. Anestopoulos; G. Tsigaridas; P. Persephonis; V. Giannetas; I. Spiliopoulos; P. Karastatiris; J. Mikroyannidis (98-103).
The linear electro-optic coefficients (Pockels coefficients) of two novel organic chromophores, doped in thin films of poly(methyl methacrylate) (PMMA), are determined through a simple experimental method based on a waveguide sample geometry. A DC electric field is applied onto each polymeric film inducing birefringence. This varies the polarization state of a laser beam passing through the film. Measuring these variations, the electro-optic coefficients can be determined for different values of the applied electric field. The microscopic molecular parameters, dipole moment μ and first order hyperpolarizability β are calculated. The results indicate that the existence of ionic bonds at the edge of the molecule of a chromophore increases its dipole moment, while the presence of strong acceptors enhances its first order hyperpolarizability.

Anomalous change in interfacial tension induced by collapses of AOT microemulsions at heptane/water interface by Masahiko Takahashi; Hiroharu Yui; Yasuhiro Ikezoe; Tsuguo Sawada (104-109).
Dynamic behavior of water-in-oil microemulsions at the oil/water interface was investigated using the quasi-elastic laser scattering method. We observed an anomalous rebound behavior of interfacial tension γ induced by collapses of microemulsions and adsorptions of AOT molecules at the interface. γ rapidly decreased and reached a minimum value (5.5 mN/m) at about 500 s after the preparation of the interface, and then increased gradually for about 2000 s to the equilibrium value (8.0 mN/m). We considered the mechanism of the rebound behavior in terms of transient change in interfacial thickness induced by the collapses of AOT microemulsions.

Intermolecular transfer integrals, and associated band-structures of organic molecular materials can be calculated through a dimer approach. Extensive numerical studies are performed on an ethylene π-dimer to investigate the basis sets dependence of transfer integrals. Convergence of calculated transfer integrals is achieved with respect to both Gaussian and plane-wave basis sets, provided the same level of theory is used. Effects of diffuse and polarization Gaussian functions on transfer integrals are identified. Comparison of experimental and theoretical values of transfer integrals of the TTF–TCNQ charge transfer salt is also presented.

We propose to use Spin-Flip (SF) methods for calculating electron transfer coupling strengths in terms of energy gaps between adiabatic states. The SF variant of Configuration-Interaction-Singles (SF-CIS) significantly improves descriptions of adiabatic states in charge-transfer systems and yields reliable energy splittings at the electron-transfer (ET) transition state. The SF-CIS scheme is more robust than the Hartree–Fock Koopmans Theorem, and its coupling dependence on intermolecular separation is correct even in diffuse basis sets. The SF approach allows for the systematic inclusion of dynamical correlation effects in electron transfer couplings. Our results indicate a small dynamical correlation effect for intermolecular electron transfer couplings.

An approach is presented to calculate the electronic spectra of molecules in solution or adsorbed on surfaces. Through limiting electronic excitations to include only those between orbitals localized on the solute or adsorbant, large computational savings are achieved with minimal additional error. This approach has been implemented within time-dependent density functional theory and single excitation configuration interaction. Calculations of the electronic spectrum of formamide in water and carbon monoxide on the Ni(1 1 1) surface illustrate the method.

Spectral broadening in a microdroplet dye laser by Anders G. Knospe; Alfred S. Kwok (130-135).
We have observed broadening of the lasing spectrum of 60-μm diameter micrdroplet dye lasers. The spectral width of microdroplet dye lasers consisting of Rhodamine 6G or Pyrromethene 597 is essentially constant when water is used as a solvent but broaden by >30% at high input-laser intensities when ethanol is used as solvent. Spectral broadening is preceded by stimulated Raman scattering of ethanol in the microdroplets as the input-laser intensity increases.

Two-photon absorption (TPA) spectra of C60 in toluene were measured for a wide wavelength region from 270 to 680 nm by femtosecond pump–probe nondegenerate TPA spectroscopy. A distinct TPA band peaked at 314 nm was observed, and its intensity was evaluated to be 80 GM. The depolarization ratio of the TPA band was found to be zero within the experimental uncertainty, which indicates that this band is due to a totally symmetric (Ag) two-photon allowed excited state. The energy of the observed Ag state is about 1 eV below a prediction based on the theoretically calculated π-electron energies.

Infrared spectra of [Mg · (H2O)1,2]+ and [Al · (H2O)1,2]+ are measured in the OH stretching region (3200–3800 cm−1). The spectra show the symmetric and asymmetric OH stretching bands of water molecules that are directly bound to the metal ions through metal–oxygen intermolecular bonds. In addition to these bands, the [Al · (H2O)2]+ ion has another band at 3714 cm−1. This band is assigned to the free OH stretching vibration of the [HO–Al–H]+ ion; the aluminum ion is inserted into the O–H bond of one water molecule in [Al · (H2O)2]+.

Time and kinetic energy resolved delayed electron emission in small carbon cluster anions by J.B. Wills; F. Pagliarulo; B. Baguenard; F. Lépine; Christian Bordas (145-150).
We present the first study of time-resolved delayed electron emission in small anionic carbon clusters. Using photoelectron velocity map imaging spectroscopy in conjunction with time-gated detection we are able to resolve delayed electron emission at different stages of the emission process. This unique capability is an essential tool to analyse pure thermionic energy spectra under well-defined conditions. The more striking result of the present work is that the effective temperature at a given delay after excitation is determined by the emission rate, rather than by the excitation energy deposited in the cluster.

Charge order, orbital order, and electron localization in the Magnéli phase Ti4O7 by V. Eyert; U. Schwingenschlögl; U. Eckern (151-156).
The metal–insulator transition of the Magnéli phase Ti4O7 is studied by means of augmented spherical wave (ASW) electronic structure calculations as based on density functional theory and the local density approximation. The results show that the metal–insulator transition arises from a complex interplay of charge order, orbital order, and singlet formation of those Ti 3d states which mediate metal–metal bonding inside the four-atom chains characteristic of the material. Ti4O7 thus combines important aspects of Fe3O4 and VO2. While the charge ordering closely resembles that observed at the Verwey transition, the orbital order and singlet formation appear to be identical to the mechanisms driving the metal–insulator transition of vanadium dioxide.

Topology of the hydrogen bond networks in liquid water at room and supercritical conditions: a small-world structure by Vivianni Marques Leite dos Santos; F.G. Brady Moreira; Ricardo L. Longo (157-161).
Monte Carlo NPT simulations were performed for water at room and supercritical thermodynamic conditions using the TIP5P model potential. The topology of the hydrogen bond patterns was characterized by local (clustering coefficient, path length and degree distribution) and global (spectral analysis) properties. The analysis was performed on 500 uncorrelated configurations at room and supercritical (500 bar and 673 K) conditions. Small-world behavior (highly clustered and small path lengths) was characterized for supercritical water, whereas for room condition, a giant cluster appears and percolates the whole system. These results might have important consequences upon using (near-) supercritical water as new reaction media.

An electron momentum spectroscopy study of the highest occupied molecular orbital of difluoromethane by G.L. Su; C.G. Ning; S.F. Zhang; X.G. Ren; H. Zhou; B. Li; F. Huang; G.Q. Li; J.K. Deng; Y. Wang (162-165).
The highest occupied molecular orbital (HOMO)of difluoromethane (CH2F2) has been firstly studied by binary (e, 2e) electron momentum spectroscopy (EMS), at the impact energy of 1200 eV plus binding energy, and using symmetric non-coplanar kinematics. The experimental momentum profile of the HOMO is compared with Hartree–Fock (HF)and density functional theory (DFT) methods with various basis sets. The experimental measurement is well described by the HF and DFT calculations except for the low-momentum region.

Au-nano-particles production by pico-second ultra-violet laser deposition in Au-ion doped PMMA film by Tomohiro Hirose; Takashige Omatsu; Masakazu Sugiyama; Susumu Inasawa; Seiichiro Koda (166-169).
We have demonstrated a novel technique for Au-nano-particle production in a polymer thin film based on the pico-second ultra-violet laser deposition. The Au-nano-particles produced by this technique were finely controlled without aggregation and the average size was ∼20 nm. We also investigated holographic grating formation in the polymer film by pico-second ultra-violet laser deposition technique.

Polarizabilities of small annulenes from Cholesky CC2 linear response theory by I. Garcı́a Cuesta; T. Bondo Pedersen; H. Koch; A.M.J. Sánchez de Merás (170-175).
Using recently developed algorithms based on Cholesky decomposition of two-electron integrals to compute response properties at the correlated level, the static and dynamic (at 589 nm) polarizabilities of [4n  + 2]-annulenes (n=1, 2, 3, 4) have been calculated. The results show that the perpendicular component increases along the series linearly with the number of double bonds. The in-plane static polarizability is also increasing linearly with the area of the aromatic ring in the case of the delocalized species. However, linearity is lost for the localized conformations and for the dynamic polarizability.

The isomerization of [H2O–CO] •+ and [HC(O)OH] •+ into [HO–C–OH] •+: proton-transport catalysis by CO by Cathy Y. Wong; Paul J.A. Ruttink; Peter C. Burgers; Johan K. Terlouw (176-180).
Mass spectrometry based experiments show that the m/z 46 ion generated in chemical ionization experiments of CO with a trace of water is not the previously proposed formic acid ion, HC(O)OH •+ (1). Instead, the more stable dihydroxycarbene ion, HO–C–OH •+ (2) is formed. A mechanistic analysis using the CBS-QB3 model chemistry supports the reaction sequence: (CO)2 •+  + H2O → H2O–CO •+ (3), followed by the CO catalyzed isomerization: 3  + CO →  2  + CO. Solitary ions 1 and 2 do not interconvert, but theory and experiment agree that CO also efficiently catalyzes the conversion 1  →  2.

Gas phase aggregates of protected clusters by Jobin Cyriac; V.R. Rajeev Kumar; T. Pradeep (181-185).
29 kDa gold cluster molecules with thiol protection were synthesized and size separated by chromatography. Their direct laser desorption leads to large scale clustering and the mass spectral features extend up to 500 kDa. Effect of alkanethiol chain length on clustering suggests that monolayer interaction is the key to this phenomenon. Role of different matrices on clustering in the matrix assisted laser desorption ionization (MALDI) process has been investigated.

A generalized exchange-correlation functional: the Neural-Networks approach by Xiao Zheng; LiHong Hu; XiuJun Wang; GuanHua Chen (186-192).
A Neural-Networks approach is employed to improve B3LYP exchange-correlation functional by taking into account of high-order contributions. The new B3LYP functional is based on a Neural-Network whose structure and synaptic weights are determined from 116 known experimental energy data [J. Chem. Phys. 98 (1993) 5648]. It leads to better agreement between the first-principles calculations and the experimental results. The new functional is further tested by applying it to calculate 40 ionization potentials and 40 enthalpies of formation in G2-2 test set [J. Chem. Phys. 109 (1998) 42] using 6-311+G(3df,2p) basis set. The root-mean-square errors are reduced from those of conventional B3LYP calculations.

We study the dielectric susceptibility of liquid hydrogen chloride at a temperature of 313 K using ab initio molecular dynamics evolving in a homogeneous electric field. For an evolution in absence of electric field, the calculated neutron structure factor shows good agreement with the experimental one, supporting the structural properties of our model. We obtain the real and imaginary parts of the dielectric susceptibility as a function of frequency from the evolution of the polarization upon the onset of an electric field. Our simulations give a static dielectric constant of 3.65, in good agreement with the measured value of 3.8.

Time dependent evolution of vanadium pentoxide nanowires in sols by Sung Joon Park; Jeong Sook Ha; Yu Jin Chang; Gyu Tae Kim (199-202).
We report on the time dependent growth of vanadium pentoxide (V2O5) nanowires in V2O5 sols prepared from ammonium (meta)-vanadate in the presence of an acidic ion exchanger at different temperatures. V2O5 nanowires were adsorbed on SiO2/Si substrate pretreated with 3-aminopropyltriethoxysilane (3-APS) and the structural evolution at 24 °C was investigated by atomic force microscope (AFM) and scanning tunneling microscope (STM). Optical absorption and current–voltage measurements confirmed the gradual growth of V2O5 nanowires with time. At the higher temperatures of the sol solution, the elongation rate of the V2O5 nanowires was enhanced, indicating the endothermic growth process.

Electronic structure near the Fermi level of the organic semiconductor copper phthalocyanine by James E. Downes; Cormac McGuinness; Per-Anders Glans; Timothy Learmonth; Dongfeng Fu; Paul Sheridan; Kevin E. Smith (203-207).
The electronic structure of thin films of the prototypical organic semiconductor copper phthalocyanine (CuPc) has been measured using resonant soft X-ray emission spectroscopy. We report the observation of two discrete states near E F. This differs from published photoemission results, but is in excellent agreement with density functional calculations. The implications of this result for the use of resonant soft X-ray emission (SXE) in the study of organic semiconductors are discussed. We also compare our data to published X-ray emission results, and show that the latter display clear evidence of beam damage.

Vibrationally resolved in situ XPS study of activated adsorption of methane on Pt(1 1 1) by T. Fuhrmann; M. Kinne; C.M. Whelan; J.F. Zhu; R. Denecke; H.-P. Steinrück (208-213).
A combination of high-resolution X-ray photoelectron spectroscopy at BESSY II and molecular beam techniques has been used to investigate the dissociative adsorption of CH4 and CD4 on a Pt(1 1 1) surface. From a detailed analysis of C 1s core-level spectra, CH3 (CD3) has been identified as the adsorbed species at 120 K, independent of the kinetic energy of the impinging methane molecules (in the range from 0.25 to 0.83 eV). The spectra show a unique fine structure, caused by vibrational excitations of C–H (C–D) stretching modes in the photoemission process. Using temperature-programmed XPS, CH is identified as the intermediate in the dehydrogenation process, forming at 260 K and further dehydrogenating to carbon above 500 K.

The molecular and electronic structures of cucurbituril (CB) and its sulfur analogue, thia-cucurbituril (TCB), have been investigated by means of density functional theory (DFT) calculations. The HOMO–LUMO (H–L) energy gap of CB is ∼7 eV and it decreases at ∼4 eV upon replacement of its twelve oxygen atoms with sulphur atoms. The vertical ionization potential (IP) of CB and TCB are rather large, being ∼7 and 6 eV, respectively. The vertical electron affinity (EA) of CB calculated in the gas-phase is negative (about −2 eV), thus suggesting that its anion is thermodynamically unstable. On the other hand, formation of the TCB anion might be favoured in electron-donating solvents since its calculated vertical EA is close to zero. An analysis of the Kohn–Sham frontier orbitals of CB and TCB indicates that neither the HOMO nor the LUMO is degenerate.

Structures and stabilities of B7, B7 + and B7 clusters by Qian-Shu Li; Liang-Fa Gong; Zhi-Ming Gao (220-227).
Ab initio (MP2) and density functional theory (DFT) calculations for six neutral (structures 16), six cationic (structures 1 +6 +) and six anionic (structures 1 6 ) isomers of B7 clusters have been performed. With only a few exceptions, all isomers are genuine minima. The hexagon capped by an atom structures (C2v symmetry) are global minima for B7 (1) and B7 (1 ) and the hexagonal pyramid structure (C6v symmetry) is the most stable B7 + (1 +). The aromatic natures of 1 and 1 +, as well as the anti-aromatic character of 1 are also discussed.

Laser-driven coherent manipulation of molecular chirality by I. Thanopulos; E. Paspalakis; Z. Kis (228-235).
A theoretical study for manipulating molecular chirality by coherent excitation dynamics using a single, linearly polarized, coherent light pulse is presented based on the dynamics of a degenerate Λ-type three-level system. General properties for various laser pulse shapes are derived within an exactly solvable analytic model. In particular, conditions for complete enantiomeric conversion on and off single-photon resonance of the intermediate state are given. The method is demonstrated on the (transiently) chiral H2S2 molecule.

The crystal structure of NaY + ND3 has been determined at 20 K by powder neutron diffraction using Rietveld analysis. The cations were located at site I (8), site II (32) and at a third site (21) in the α-cage. This reveals a substantial migration of the cations from the site I, which is totally emptied, and the site I to large cages. The ND3 are in electrostatic interaction with the Na+-counter-ions and in hydrogen bonding interaction with the framework oxygen atoms. This double interaction is for the first time experimentally evidenced on cationic zeolite upon ammonia adsorption.

Kinetics of salt-induced J-aggregation of an anionic thiacarbocyanine dye in aqueous solution by Alexander K. Chibisov; Helmut Görner; Tatyana D. Slavnova (240-245).
The kinetics of J-aggregation of 3,3-di(γ-sulfopropyl)-5-methoxy-4,5-benzo-9-ethylthiacarbocyanine in aqueous solution was studied in the presence of salts. The rate of formation of J-aggregates increases with both dye and salt concentrations, is highest for trivalent metal ions, moderate for divalent and smallest for monovalent ions and independent of the type of anion. The growth of J-aggregates is reflected in absorbance and fluorescence and accompanied by a corresponding decrease of the dimer concentration. The formation of J-aggregates is described by a sigmoidal time course. The kinetics and mechanism of J-aggregation are rationalized in terms of autocatalysis and the relevant parameters were determined by fitting procedures.

Current–voltage curves for molecular junctions: pyrene vs diphenylacetylene by Charles W. Bauschlicher; Alessandra Ricca; Yongqiang Xue; Mark A. Ratner (246-249).
The IV curves are computed for 2,7-dithiolpyrene and 4,4-dithiol-diphenylacetylene between two Au(1 1 1) surfaces. For a given bias, up to about 2.5 eV, the current for 2,7-dithiolpyrene is about half that for 4,4-dithiol-diphenylacetylene. However, the fused benzene rings in 2,7-dithiolpyrene eliminate the loss of current associated with rotation about the central C2 that can occur for 4,4-dithiol-diphenylacetylene.

Pronounced out-of-plane diffraction of H2 molecules from a Pd(1 1 1) surface by D. Farı́as; C. Dı́az; P. Nieto; A. Salin; F. Martı́n (250-255).
We have measured the angular distribution of H2 molecules with incident energies 100–150 meV reflected by the Pd(1 1 1) surface at 430 K. In spite of the low diffraction reflectivity (∼0.5%), diffraction peaks have been resolved at nearly grazing incidence. Apart from specular reflection, out-of-plane diffraction has been found to be dominant, in agreement with classical simulations. We show that this behavior is a generic one for grazing incidence and discuss the relevance of this finding for the study of molecule/surface dynamics in systems for which dissociation is a non activated process.

A study on stabilization of HHeF molecule upon complexation with Xe atoms by Antti Lignell; Leonid Khriachtchev; Markku Räsänen; Mika Pettersson (256-260).
In the present work, we computationally study energetic stabilization of HHeF by its complexation with Xe atoms. For the studied HHeF⋯Xe n systems (n=1–4,6), we found a large complexation-induced decrease of energy of HHeF with respect to its dissociation into atoms. As a working hypothesis, we assume that this stabilization effect continues for the larger systems (n>6) as well. This suggests that dissociation of HHeF via the H–He stretching coordinate might be suppressed and its lifetime might be increased by inserting it into large Xe clusters or matrices.

Electrochemical reductive cleavage of carbon tetrachloride at glassy carbon electrodes in various non-aqueous solvents follows a quadratic activation-driving force dynamics whereas the Butler-Volmer kinetics is observed in the case of benzonitrile. A relatively higher transfer coefficient value has been noticed in benzonitrile, while in rest of the solvents, the transfer coefficients are less than 0.5. In benzonitrile, both the electron transfer and bond cleavage occur in a single step with a linear activation-driving force relationship, as deduced from the low temperature voltammetric studies in conjunction with the convolution analysis.

Understanding proton magnetic shielding in the benzene molecule by M.B. Ferraro; P. Lazzeretti; R.G. Viglione; R. Zanasi (268-271).
According to the ring current model quoted in textbooks of nuclear magnetic resonance spectroscopy, the downfield chemical shifts of hydrogen nuclei in aromatic molecules is due to intense delocalized currents induced in the π-electron cloud by a magnetic field at right angles to the molecular plane. By using the Biot-Savart law, it was found that the delocalized ring currents deshield the out-of-plane component of proton shielding tensor via an essentially local mechanism taking place in the close vicinity of protons. The π ring currents over distant carbons shield the protons. π and σ electrons deshield benzene protons via different mechanisms clearly observed in plots of the shielding density function defined in the text. These results provide a novel interpretation of the phenomenology and suggest that the familiar model for interpreting chemical shifts of aromatics should be revised.

Clusters of 2-methoxyphenol (2MP) with one and two water molecules have been studied using R2PI and IR/R2PI. Under microhydration the intramolecular hydrogen bond between the OH and OCH3 groups is destroyed. One water molecule is inserted between both substituents forming a cyclic structure with 2MP. The OH stretching band of 2MP is red shifted by 122 cm−1 relative to the monomer. Two water molecules form a dimer bridge with less strained H-bonds. The two H-bonded OH stretches of the water dimer exhibit red shifts of 205 and 230 cm−1. The larger red shifts result from stronger H-bonds, as compared to similar clusters with phenol. The experimental data are supported by the calculations.

Experimental and theoretical study of the vibrational spectrum, structure and electron density distribution of the [2-CB10H11] anion by E.G. Kononova; L.A. Leites; S.S. Bukalov; A.V. Zabula; I.V. Pisareva; V.E. Konoplev; I.T. Chizhevsky (279-284).
The presence of two low-frequency large-amplitude modes in the vibrational spectrum, experimental and computed data on B–B interatomic distances and the results of a topological analysis of the electron density distribution in the molecule of an 11-vertex monocarbaborate [2-CB10H11] lead to the conclusion that this polyhedron is not rigid, missing at least four double-center B–B bonds and thus being formed not only by triangular faces. Hence, this carbaborane does not have the closo-structure traditionally ascribed to it on formal [2n+2]-electron count grounds.

Reversibly strain-tunable elastomeric photonic crystals by Jian Li; Yang Wu; Jun Fu; Yang Cong; Juan Peng; Yanchun Han (285-289).
Reversibly strain-tunable polymeric photonic crystals made of thermoplastic polyester elastomer (TPEE) were fabricated by using the self-assembled silica opals as templates. The stop band of the polymeric photonic crystal locates at the near infrared (IR) regime in its transmission spectrum, and exhibits a blue shift with the increase of the incident angle. Because of the elasticity of the TPEE, the stop band of the TPEE photonic crystal can also be reversibly tuned at ambient temperature through to and fro uniaxially or biaxially stretching and recovering by changing the lattice spacing and the symmetry of the crystal along (1 1 1) plane.

We present a first demonstration of `mode-locked' cavity-enhanced absorption spectroscopy (ML-CEAS) using a mode-locked diode-pumped, vertical external-cavity, surface-emitting semiconductor laser (DP-VECSEL). This laser, operating around 1.04 μm, was modeloked using a semiconductor saturable absorber mirror (SESAM) and provided an emission spectrum possessing a regular comb of modes with a broad and smooth envelope. Matching this comb with the comb of resonances of a high finesse cavity allowed efficient transmission of the laser spectrum by the cavity. Thanks to the enhancement of absorption by the cavity, on this transmitted spectrum we could observe weak absorption lines by a gas placed inside the cavity.

High-quality tetrapodlike ZnO nanocrystals (T-ZnONCs) were synthesized on ZnO catalyzed Si substrate through a modified vapor transport process, in which zinc carbonates was used as a zinc source to yield supersaturated zinc vapor. The T-ZnONCs were self-assembled by a tetrahedral core and four cylindrical nanorods (arms) with the diameter of 60–80 nm. Three luminescence bands, namely UV band at 380 nm, violet band at 440 nm and green emission at 506 nm, were identified in their photoluminescence spectrum. The strengthened UV emission implied that the cylindrical (rather than needlelike) arms improved the lattice integrity of the T-ZnONCs.

I.M. Irurzun, R.B. Hoyle, M.R.E. Proctor and D.A. King [Chem. Phys. Lett. 377 (2003) 269] have recently proposed a novel coarse-grained approach to describing the transport of adsorbed CO molecules along the quasi-hexagonal and (1 × 1) patches during kinetic oscillations in CO oxidation on the Pt(1 0 0) surface. Our analysis indicates that this approach cannot be used as a robust tool for analysing the pattern formation in oscillatory catalytic reactions, because it contradicts the basic principles of general theory of mass transport.

Reply to `Comment on `Modelling pattern formation in CO + O2 on Pt{1 0 0}” by I.M. Irurzun; R.B. Hoyle; M.R.E. Proctor; D.A. King (305-306).
We respond to the comment of V.P. Zhdanov on our earlier Letter [Chem. Phys. Lett. 377 (2003) 69]. We give an explicit account of the derivation of our coarse-grained equations for the spatial variation of CO coverages.