Chemical Physics Letters (v.427, #4-6)

Contents (iii-xiv).

Terahertz (THz) spectroscopy of Freon-11 (CCl3F, CFC-11) at room temperature by H. Altan; B.L. Yu; S.A. Alfano; R.R. Alfano (241-245).
The rotational absorption spectrum for the ground state of Freon-11 has been measured on the part per thousand levels by volume for the first time using time-resolved THz Spectroscopy.The rotational spectrum for the lowest vibrational mode for CCl3F has been measured in the 0.1–2 THz frequency range using a compact time-resolved terahertz spectrometer. The peak of the population spectrum for the ground state rotational manifold was observed at 0.3 THz. The observed absorption profile was modeled with rotational and vapor pressure parameters. The limits of detectivity of the compact THz system are discussed in context of atmospheric sensing.

Low temperature behaviour of collisions between antiprotonic helium and hydrogenic molecules and an indication of the Wigner threshold law by B. Juhász; D. Barna; J. Eades; H. Fuhrmann; R.S. Hayano; M. Hori; D. Horváth; H.A. Torii; E. Widmann; H. Yamaguchi; T. Yamazaki; J. Zmeskal (246-250).
The temperature dependence of the quenching cross section of the long-lived metastable state (n,  l) = (39, 35) of antiprotonic helium, in collisions with deuterium molecules, has been measured. It was found that it increases slightly with decreasing temperature, indicating the 1/v Wigner threshold law of exothermic reactions involving neutral particles.The temperature dependence of the quenching cross section of two long-lived metastable states of antiprotonic helium, in collisions with hydrogen and deuterium molecules, has been measured. In the case of the state (n,  l) = (37, 34), the cross section decreases with decreasing temperature until it levels off below ∼30 K, showing a quantum tunneling effect with a small activation barrier. In the case of the state (39, 35), on the other hand, for which the lack of an activation barrier was predicted theoretically, the quenching cross section increases slightly with decreasing temperature, indicating the 1/v Wigner threshold law of exothermic reactions involving neutral particles.

Emission of PEG (polyethylene glycol) molecules and ions from an ice target induced by laser irradiation in the infrared (IR) regime at 1064 nm was studied. Matrices of 1% weight PEG flash-frozen solutions were used for polymer deposition with MAPLE (matrix-assisted pulsed laser evaporation).Emission of PEG (polyethylene glycol) molecules and ions from an ice target induced by laser irradiation in the infrared (IR) regime at 1064 nm was studied. Matrices of 1% weight PEG flash-frozen solutions were used for polymer deposition with MAPLE (matrix-assisted pulsed laser evaporation). Even though linear absorption in defect-free water ice is two orders of magnitude larger at 1064 nm than 355 nm, the deposition rate and ion current density are much smaller for IR than for ultraviolet laser light. The similarity of results for both wavelengths indicates that non-linear absorption by electrons via optical breakdown is dominant.

Intact molecular ion formation of cyclohexane and 2,3-dimethyl-1,3-butadiene by excitation with a short, intense femtosecond laser pulse by Michinori Tanaka; Subhasis Panja; Masanao Murakami; Tomoyuki Yatsuhashi; Nobuaki Nakashima (255-258).
Cyclohexane was ionized and fragmented at a typical intensity of 4 × 1013  W cm−2 at 15 fs with 0.8 μm femtosecond pulses as shown in the figure. Short pulse excitation is effective to produce molecular ion and that the mechanisms should be analyzed.Cyclohexane and 2,3-dimethyl-1,3-butadiene (DMBD) were ionized and fragmented by 0.8 μm femtosecond pulses with a typical intensity of 4 × 1013  W cm−2, which were resonant with the cation absorption of cyclohexane and DMBD. Their intact molecular ions were dominant at a pulse duration of 15 fs, whereas the molecules were heavily fragmented by excitation at 205–210 fs. Possible reasons for the formation of intact molecular ions by a short pulse are discussed in terms of the vibrational periods of excited precursor states.

Resonant optical excitation of the I2 ion-pair states through the RgI2 complexes in the valence states correlating to the 2P1/2  +  2P1/2 limit by M.E. Akopyan; A.A. Buchachenko; S.S. Lukashov; I.Yu. Novikova; S.A. Poretsky; A.M. Pravilov (259-264).
Luminescence spectra of I2(β1g,ν β  ⩽ 59, D 0 u + ,ν D  ⩽ 61) ion-pair states are observed in I2  + Rg mixtures after irradiation by Nd:YAG laser. Excitation is attributed to 1064.48 + 532.24 nm pumping of RgI2 complexes in 0 g + ,1u(2P1/2  +  2P1/2) states. Subsequent decay of the complexes gives free I 2 ( 1 u , 0 g + ) molecules, which are excited to the ion-pair states by third 532.24 nm photon.The luminescence spectra of I2(β1g,ν β  ⩽ 59 and D 0 u + , ν D  ⩽ 61) ion-pair states are observed in I2  + Rg mixtures after irradiation by Nd:YAG (1064.48 and 532.24 nm) laser beams. Luminescence excitation is attributed to two-step 1064.48 + 532.24 nm pumping of RgI2 complexes in 0 g + and 1u valence states correlating to third valence dissociation limit 2P1/2  +  2P1/2. Subsequent decay of the complexes gives free I 2 ( 1 u , 0 g + ) molecules, which are excited to the β1g and D 0 u + states by third 532.24 nm photon. This mechanism conforms all experimental findings and provides the first indication for optical population of the RgI2 complexes in the valence states different from the B 0 u + and X 0 g + .

The catalytic effect of water in the dehydration reaction between VO+ and NH3 to yield VNH+ and H2O has been rationalized by means of DFT calculations. This catalysis can be associated to a water assisted rearrangement along a proton relay mechanism.On the basis of DFT calculations, an understanding on the catalytic effect of water in the dehydration reaction between VO+ and NH3 to yield VNH+ and H2O has been obtained. The Gibbs free energy profiles point out that the global process involves two consecutive hydrogen shifts from the nitrogen to the oxygen atom. The catalytic role is achieved by a water assisted mechanism in which water acts as proton donor and acceptor, via transition structures corresponding to a six-membered rings. The corresponding stationary points lie below both the entrance VO+  + NH3, and VNH+  + H2O, channels.

Theoretical study of activation C―O bond of CH3OCH3 by Ti+ in the gas phase by Yong-Cheng Wang; Ze-Yu Liu; Zhi-Yuan Geng; Xiao-Yan Yang (271-275).
The gas-phase reaction of activation C―O bond of CH3OCH3 by Ti+ has been investigated using DFT. CPs between quartet and doublet electronic states are localized. Two competitive reaction pathways, including the CP, are proposed from the most stable reactants to the most thermodynamically stable products.The gas-phase reaction of activation C―O bond of CH3OCH3 by Ti+ has been investigated using density functional theory (DFT) at the 6-311++G(3df,3pd)//6-311+G(d) level. The structures of all reactants, intermediates, transition structures and products of this reaction have been optimized and characterized at the quartet and doublet electronic states. Crossing points (CPs) are localized, and the possible spin inversion processes are discussed by means of the intrinsic reaction coordinate (IRC) approach. Finally, two competitive reaction pathways, including the CP, are proposed from the most stable reactants to the most thermodynamically stable products.

Rate coefficients for the hydrogen atom abstraction reactions of several substrates including halogenated organic compounds and amines by t-butoxy radical have been determined together with the Arrhenius parameters, transition states and activation barriers for selected reactions.By using Fourier-Transform Infrared (FTIR) absorption spectroscopy, rate coefficients in the range of 10−16 to 10−14  cm3  molecule−1  s−1 have been determined for the hydrogen atom abstraction reactions of several substrates including halogenated organic compounds and amines by t-butoxy radical generated from the uv photolysis of t-butyl nitrite in the gas phase. Arrhenius parameters for selected reactions have been measured in the temperature range 299–318 K. Transition states and activation barriers for such reactions have been computed with the help of Gaussian 03 software and found to match very well with the experimental values.

Relativistic calculation of NMR properties of XeF2, XeF4 and XeF6 by Andrej Antušek; Magdalena Pecul; Joanna Sadlej (281-288).
Non-relativistic Hartree–Fock, MP2 and CCSD and relativistic Dirac–Hartree–Fock calculations of NMR shielding and spin–spin coupling constants of xenon fluorides of XeF2, XeF4, and XeF6 are presented and the results are compared with available experimental and theoretical data.Non-relativistic Hartree–Fock (HF) and relativistic Dirac–Hartree–Fock (DHF) calculations of the NMR shielding and spin–spin coupling constants of xenon fluorides XeF2, XeF4 and XeF6 are presented and the results are compared with the available experimental and theoretical data. Relativity contributes approximately 1000 ppm to the 129Xe shielding constants in XeF2 and XeF4, and nearly 500 ppm in XeF6, and the DHF results are close to the experiment. They are less consistent with the experiment for the 19F shielding constants, more sensitive to electron correlation than to relativity. The calculated coupling constants agree well with experiment for XeF2 and XeF4, but not for XeF6.

Self-aggregation as a source of chiral discrimination by Ibon Alkorta; Krzysztof Zborowski; José Elguero (289-294).
The theoretical study of the hydrogen peroxide clusters, (HOOH) n , from 2 to 10 monomers shows that for n  = 2 and 3, the cluster with mixed chirality are favoured while for larger clusters, the homochiral cluster are favoured.A theoretical study of the hydrogen peroxide clusters, (HOOH) n , from 2 to 10 monomers, has been carried out using DFT/B3LYP and MP2 ab initio methods. The results show that for n  = 2 and 3, the cluster with mixed chirality is preferred while for larger clusters, the homochiral cluster is favoured. The Optical Rotatory Power and Vibrational Circular Dichroism spectra of some of the systems have been calculated and analyzed.

Picosecond fluorescence decay of Soret-excited zinc tetraphenyl porphyrin in toluene and methanol.The model metalloporphyrin, ZnTPP, has been excited in its Soret absorption band at 400 nm in several solvents and its decay dynamics measured by fluorescence upconversion. The linear relationship between the Lorenz–Lorentz polarizability function and S2–S1 electronic energy gap strongly suggests that the only significant radiative state is the 2(1Eu) state directly populated on Soret excitation. The energy gap law of radiationless transition theory has been shown to apply to the limited case of the relaxation rates of the S2 state of ZnTPP in these fluid solvents at room temperature, but does not apply to other zinc porphyrins.

Vibrational spectra of crystalline hydrates of atmospheric relevance: Bands of hydrated protons by Beatriz Martı´n-Llorente; Delia Fernández-Torre; Vı´ctor J. Herrero; Ismael K. Ortega; Rafael Escribano; Belén Maté (300-304).
Vibrational spectra of crystalline hydrates are calculated with a DFT methodology. Comparison with experiment shows bands of hydrated protons to be very broad, the width growing with increasing number of hydration water molecules.Theoretical absorption spectra of HCl trihydrate, HCl hexahydrate, and HNO3 trihydrate in the mid-IR have been calculated using the Siesta suite of programs, a DFT method especially designed for periodic systems of large size. Infrared intensities are obtained from the macroscopic polarization changes per normal mode. The theoretical results can account globally for the observed experimental features. In all spectra, the largest absorption intensities are due to stretching vibrations of hydrated oxonium ions. Oxonium stretching absorptions appear as broad bands in the experimental spectra, with band widths growing with increasing number of water molecules coordinated to the H3O+ ion.

From intensity of red/green ratio versus probe position at 2.5 mA/cm2, position of exciton accumulation is determined to be at 10 nm at which peak intensity ratio is. As deduced from the electrical current at 8 V versus probe position, the benefit of current increase results from the higher recombination coefficient of the probe.In this Letter, we had measured the spatial recombination-rate distribution of a mixed-emitter organic light-emitting device by inserting a red-dopant at different positions of the emitting layer as a probe. The approach of thin doped-layer to the maximum recombination-rate position generated a strong red emission. In the meantime, the electrical current increased by 8.12 times at 8 V due to the higher recombination coefficient of the dopant than the matrix. In our ME-EML, the maximum recombination-rate position was 10 nm to the hole-transport layer. Carrier piled-up near the EML and the electron-transport layer interface was concretely observed.

The role of charge-enhanced C–H⋯O interactions in gel-like mixtures prepared from ionic liquids and tungsten(VI) oxide nanoparticles by Hai-Chou Chang; Jyh-Chiang Jiang; Wei-Cheng Tsai; Guan-Ciao Chen; Sheng Hsien Lin (310-316).
The high pressure studies demonstrate that the imidazolium C–H⋯O3W interactions can offer an additional stability to perturb the local structure of 1,3-dimethylimidazolium methyl sulfate. Such a molecular ordering may trigger clustering of the surrounding anions and cations and interconnect neighboring WO3 nanoparticles to form physical gel.Gel-like mixtures were prepared by mixing 1,3-dimethylimidazolium methyl sulfate with tungsten(VI) oxide nanopowder. Close interactions of the charge-enhanced C–H⋯O type have been analyzed via high-pressure infrared and Raman spectroscopy. The presence of tungsten(VI) oxide nanopowder has a negligible effect on the peak frequency of the methyl C–H stretching band. However, the pressure dependence of imidazolium C–H stretching modes displays significant changes as tungsten(VI) oxide nanoparticles were added. The results demonstrate that the imidazolium C–H⋯O3W interactions can offer an additional stability to perturb the local structure of 1,3-dimethylimidazolium methyl sulfate. Such a molecular ordering may trigger clustering of the surrounding anions and cations and interconnect neighboring WO3 nanoparticles to form physical gel. Raman spectra of a gel-like 1,3-dimethylimidazolium methyl sulfate/tungsten(VI) oxide mixture revealed a new low energy band at 788 cm−1. We attribute the 788 cm−1 band to the interactions between the ionic liquid and surface WO3.

Phase manipulation of continuum generation and stimulated Raman scattering in ethanol by Anjan Barman; Nicholas T. Form; Benjamin J. Whitaker (317-321).
By tailoring the spectral phase of a femtosecond pulse which is weakly focused into a solution it is possible to tune continuum generation in the solvent so as to excite a dye molecule dissolved in the solution.Phase modulated light pulses from a non-collinear optical parametric amplifier are used to manipulate the fluorescence intensity of a dye in ethanol solution. The spectrum of the exciting light is centered well to the red of the absorption spectrum of the dye but by tailoring the spectral phase we are able to control continuum generation within the solvent in such a way that the high frequency tail of the continuum spectrum overlaps the absorption spectrum of the dye. In a similar fashion we also demonstrate an ability to tune an intense spot of stimulated Raman emission laterally through the cuvette containing the solvent.

External electric field effects on fluorescence of perylene doped in a polymer film by Anjue Mane Ara; Toshifumi Iimori; Tomokazu Yoshizawa; Takakazu Nakabayashi; Nobuhiro Ohta (322-328).
Electrofluorescence spectra of perylene doped in a PMMA film at a concentration of 3 mol%. Excimer fluorescence shows a field-induced enhancement at room temperature, whereas it shows a field-induced quenching at low temperatures.Fluorescence and electrofluorescence spectra of perylene molecules doped in a polymer film at different concentrations have been measured at different temperatures in the range of 70–295 K. At high concentrations where excimer is formed, LE fluorescence emitted from the locally excited state of perylene is quenched by an electric field at any temperature, indicating a field-induced enhancement of the excimer formation rate. Fluorescence of the Y-type excimer of perylene molecules shows a field-induced enhancement at room temperature, whereas it shows a field-induced quenching at low temperatures. The temperature dependence of the electric field effects on fluorescence has been discussed.

We report the measurements of CARS signal spatial distribution of three room-temperature ionic liquids, C n mim[PF6] (n  = 4, 6, 8). The result suggests that specific local structures with a mesoscopic size are formed and that the dimension of these local structures increases with increasing the alkyl-chain length n.We measure the spatial distribution of the coherent anti-Stokes Raman scattering (CARS) signal from three room-temperature ionic liquids, 1-alkyl-3-methylimidazolium hexafluorophosphates, where alkyl is butyl, hexyl, and octyl. The spatial distribution pattern becomes narrower as the alkyl-chain length increases. This result suggests that, although these ionic liquids are uniform and transparent macroscopically, specific local structures are formed with their size increasing with the alkyl-chain length. From the broadening mechanism of the CARS spatial distribution, it is most likely that the size of local structures in these ionic liquids is in the range of several tens of nanometers.

Ferromagnetic exchange coupling was operative between nickel(II) spins in a dinuclear nickel(II) complex [{Ni(hfac)2}2(py4C)] owing to the orthogonal arrangement of the magnetic orbitals (py4C = tetrakis(2-pyridyl)methane).Ferromagnetic exchange coupling was operative between nickel(II) spins in a dinuclear nickel(II) complex [{Ni(hfac)2}2(py4C)] with J/k B  = +0.57(2) K (H  = −2JS 1  ·  S 2), where hfac and py4C stand for 1,1,1,5,5,5-hexafluoropentane-2,4-dionate and tetrakis(2-pyridyl)methane, respectively. X-ray crystal structure analysis revealed an approximate D2d symmetry of the [Ni(py4C)Ni] core and accordingly the orthogonal arrangement between the two coordination basal planes. Mechanism of the ferromagnetic coupling was proposed on the basis of the orthogonal dσ-type magnetic orbitals, which was supported by DFT calculation.

Phosphorous atom induced intramolecular charge transfer fluorescence in 9-diphenylphosphinophenanthrene by Masahisa Osawa; Mikio Hoshino; Tatsuo Wada; Yasuyuki Araki; Osamu Ito (338-342).
9-Diphenylphosphinophenanthrene (9DPP) in solutions at 298 K gives a broad ICT fluorescence spectrum centered at 510 nm in n-hexane. The origin of the ICT fluorescence is discussed on the basis of X-ray structure analysis, solvent effects on fluorescence, and MO calculations by contrast with 9-diphenylaminophenanthrene (9DAP).9-Diphenylphosphinophenanthrene in solutions at 298 K gives a broad ICT fluorescence spectrum centered at 510 nm in n-hexane. The origin of the ICT fluorescence is discussed on the basis of X-ray structure analysis, solvent effects on fluorescence, and MO calculations by contrast with 9-diphenylaminophenanthrene. The weak interaction between the non-bonding sp3 orbital of the P atom and the π orbital of the phenanthrene moiety in the ground state is considered to promote the intramolecular charge transfer in the excited singlet state, leading to the ICT fluorescence.

Isomorphous substitution of the perchlorate ion with tetrafluoroborate in the bis(N,N-diethylethylenediamine) salt results in increase of the temperature of the photoinduced phase transition of about 30 K.The continuous temperature-induced change of the ligand field strain in a pseudo-Jahn–Teller thermochromic crystal bis(N,N-diethylethylenediamine)copper(II) tetrafluoroborate was studied. In situ powder photodiffraction was employed to demonstrate that at the low-temperature limit of the gradual lattice stability another structural phase transition can be triggered by photoinduction of the intramolecular ligand-to-metal charge transfer. The minute differences in the cationic structure imposed by the isomorphic ionic substitution result in increase of the temperature of the photoinduced phase transition of about 30 K relative to the perchlorate salt.

In this work, NMR T 1 and T 2 relaxation times of the protons of the dibenzo diaza 18-crown-6 ether derivative (N,N -dihexyl-7,16-diaza-1,4,10,13-tetraoxa-2,3,11,12-dibenzo-cyclooctadeca-2,11-diene) were measured at 400 MHz. A 4th order equation was derived for the correlation time, τ from the ratio of (1/T 1)/2(1/T 2). Then the equation was solved to calculate τ using the experimental data obtained for the (1/T 1)/2(1/T 2). The τ data suggested that overall molecular tumbling is the source of the relaxation.Spin–lattice (T 1) and spin–spin (T 2) relaxation times of seven peaks in dibenzo diaza 18-crown-6 ether derivative were measured at 300K with a Bruker 400 MHz NMR spectrometer. An equation was derived for correlation time τ from the ratio of the (1/T 1)/2(1/T 2) using relaxation formulas pertaining to dipolar interactions. The correlation time was calculated from the equation for each peak using experimental data for (1/T 1)/2(1/T 2) ratio. The estimated τ values ranged from 0.7 ns to 2 ns. The similarity of τ values of the peaks belonging to the different parts of the molecule suggested that overall molecular tumbling may be responsible for relaxation mechanism of all the groups.

Formation and growth mechanism of tungsten oxide microtubules by Shiliang Wang; Yuehui He; Baiyun Huang; Jin Zou; C.T. Liu; P.K. Liaw (350-355).
Aggregation mechanism based on CVD process: (a) formation of W18O49 leader crystal; (b) secondary whiskers growth parallel to the leader whiskers; (c) the initial stage of the aggregation of the whiskers; (d) formation of long hollow tubules by continuous CVD growth.Tungsten oxide microtubules, arrayed in a radial flower-like structure, were synthesized by simply using W powders reacting with Ni(NO3)2  · 6H2O at a elevated temperature. The formed microtubules, with lengths more than 100 μm and outer diameters of 1–5 μm, have irregular open ends, showing clear grooves along the growth direction on the tubule surface. A novel aggregation mechanism based on chemical-vapor-deposit process was proposed to describe the growth process of the synthesized tubules, and the possible mechanism for the arrangement of the radial flower-like morphology was discussed.

Solubility of (NH4)2SiF6, K2SiF6 and Na2SiF6 in acidic solutions by Jérôme Frayret; Alain Castetbon; Gérard Trouve; Martine Potin-Gautier (356-364).
This graphical abstract present the spatial disposition of the three studied hexafluorosilicates. The formula of the solubility for these compounds is given according to the different concentrations of the elements constituting the initial hexafluorosilicate.Experimental values for the solubilities of three alkaline salts of hexafluorosilicate (K2SiF6, Na2SiF6 and (NH4)2SiF6) in different acidic solutions are reported as a function of the acid concentration in the solution. The acids used for this Letter are hydrofluoric, hydrochloric, sulphuric and nitric acids. The solubilities of the three studied compounds present important variations according to the nature and the concentration of the acidic solution. The presence of these acids influences the ionic strength of the solution, which plays an important role on the solubilisation of the three studied hexafluorosilicates. Fit curves have been elaborated to characterize the solubilisation phenomenon of the three compounds in the studied acidic solutions.

The interaction energy between a graphene sheet and a catalytic substrate-supported metal cluster has been studied by classical molecular dynamics simulation, in the wider context of a multi-scale modelling investigation of the growth process of single wall carbon nanotubes (SWNTs).The interaction energy between a graphene sheet and a catalytic substrate-supported metal cluster has been studied by classical molecular dynamics simulation, in the wider context of a multi-scale modelling investigation of the growth process of single wall carbon nanotubes (SWNTs). The contact angle of the metal cluster on the substrate is proportional to the binding energy of the potential function representing the interaction between the metal cluster and the substrate, and the total interaction energy between the metal cluster and the graphene sheet depends on contact angle. However, the interaction energy per unit area was found to be 1.0 eV Å−2 (16.03 J m−2), independent of the contact angle, using Ni as catalyst.

Growth of single crystalline Zn x Cd1−x S nanocombs by metallo-organic chemical vapor deposition by Tianyou Zhai; Xinzheng Zhang; Wensheng Yang; Ying Ma; Jianfeng Wang; Zhanjun Gu; Dapeng Yu; Hui Yang; Jiannian Yao (371-374).
Single crystalline Zn x Cd1−x S nanocombs were prepared by a one-step metallo-organic chemical vapor deposition. The asymmetric growth behavior of the nanocombs is likely to be induced by the polarization of the c-plane.Single crystalline ternary Zn x Cd1−x S nanocombs, which have ‘comb’ shaped teeth on one side, have been synthesized by a one-step metallo-organic chemical vapor deposition process at a low temperature of 420 °C. The asymmetric growth behavior of the nanocombs is likely to be induced by the polarization of the c-plane. Because of the uniform structure and perfect geometrical shape, the nanoteeth could be potentially useful as nanocantilever arrays for nanosensors and nanotweezers.

Efficient optical materials based on fluorinated-polymeric silica aerogels by O. García; R. Sastre; D. del Agua; A. Costela; I. García-Moreno; A. Roig (375-378).
New hybrid solid-state dye laser materials based on highly porous silica aerogels saturated with laser dye PM567 dissolved in fluorinated copolymers have been synthesized. Remarkable lasing efficiency of up 32% was recorded with a highly stable laser operation with no sign of degradation in the laser output after 100,000 pump pulses in the same position of the sample under transversal pumping (532 nm), at 30 Hz repetition rate.New hybrid solid-state dye laser materials based on highly porous silica aerogels saturated with laser dye pyrromethene 567 dissolved in copolymers of methyl methacrylate with different volumetric proportion of different fluorinated monomers have been synthesized. Remarkable lasing efficiency of up 32% was recorded with a highly stable laser operation with no sign of degradation in the laser output after 100,000 pump pulses in the same position under transversal pumping with 532 nm at 30 Hz repetition rate. These results make very promising the approach used in this work to enhance the lasing action of dye laser doped hybrid solid-state materials.

Adsorption behavior of formate (HCOO) on Ni(1 1 0) surface has been investigated using a scanning tunneling microscope (STM) at cryogenic temperature. L- and S-formates assemble to form dimers, trimers and short chains through thermal diffusion. This characteristic development of the formate chain is caused by anisotropic lateral interaction between neighboring formate molecules.Adsorption behavior of formate (HCOO) on Ni(1 1 0) surface has been investigated using a scanning tunneling microscope (STM) at cryogenic temperature. Formic acid (HCOOH) is found to dissociatively adsorb onto Ni(1 1 0) to produce formate at 50 K. Atomically resolved STM images revealed that formates can occupy either short-bridged (S-formate) or long-bridged (L-formate) sites at 50 K. At low surface coverages, formates are isolated and disordered when dosed at 50 K. Annealing of the Ni(1 1 0) surface to 120 K induces site conversion of L-formate to S-formate, indicating L-formate is a metastable state formed only at low temperature. Furthermore, L- and S-formates assemble to form dimers, trimers and short chains through thermal diffusion. This characteristic development of the formate chain is caused by anisotropic lateral interaction between neighboring formate molecules.

Two silver nanowires with elliptical cross-section and different surface to surface distances d interact with linearly (y-)polarized light leading to different near-field patterns as shown in the pictogram. In the case of ellipses with major axes along the polarization axis, complex optical spectra arise with size and position varying resonance peaks, and a noticeable enhancement of the scattering cross-sections.The interaction of light with isolated and pairs of silver nanowires with ellipsoidal cross-sections is studied with the finite-difference time-domain (FDTD) method. A Drude model frequency-dependent dielectric constant, with parameters fit to empirical data, is employed. We determine the optical spectra, surface plasmon resonances and near-field profiles for various eccentricities and alignments relative to linearly polarized light. For one nanowire, the surface plasmon resonance position red (to a larger extent) and blue shifts as the ellipse is further elongated when the major (long) axis of the ellipse is oriented along or perpendicular to the direction of incident polarization. We also consider the case of two silver nanowires with circular and ellipsoidal cross-sections.

Surface transformation of carbon nanotube powder into super-hydrophobic and measurement of wettability by Yong Cheol Hong; Dong Hun Shin; Soon Cheon Cho; Han Sup Uhm (390-393).
The Owens–Wendt plot using the contact angles of CNT powders with three liquids. The total surface free energies for CNTs before/after NF3-plasma were calculated to be 82.6 mJ/m2 and to 0.12 mJ/m2 for 10 min plasma-treated CNT powder. Dispersion-behaviours of CNT powders in water are shown in the inset of figure.Super-hydrophobic carbon nanotube (CNT) powders were formed by NF3 glow-discharge plasma at low-pressure and their surface free energies were directly determined from the contact angles with probe liquids using the Owens–Wendt plotting. The cushion made of plasma-treated CNT powders revealed super-hydrophobicity (contact angle > 153°), regardless of kinds of probe liquids and treatment-time. The surface free energy of the NF3 plasma-treated CNT powders decreased drastically from 82.6 to 0.12 mJ/m2. The plasma treatment using fluorinated compound gases may be useful for dispersing, separating, and cutting CNTs since CNTs have tendency to aggregate in bundles and poor solubility.

Mild oxygen plasma treated PEDOT:PSS as anode buffer layer for vacuum deposited organic light-emitting diodes by Yunfei Zhou; Yongbo Yuan; Jiarong Lian; Jie Zhang; Hongqi Pang; Lingfang Cao; Xiang Zhou (394-398).
The uniformly distributed nanometer-scale islands on the surface of PEDOT:PSS layer formed by mild oxygen plasma treatment have been observed and OLEDs with the appropriately treated PEDOT:PSS layer as anode buffer layer exhibited enhanced lifetime and decreased driving voltage.The surface morphology of PEDOT:PSS after mild oxygen plasma treatment were investigated by scanning electron microscopy and atomic force microscopy. The nanometer-scale islands on the surface of treated PEDOT:PSS were observed. Vacuum deposited organic light-emitting diodes (OLEDs) with treated PEDOT:PSS as anode buffer layer had been fabricated. The OLEDs with an appropriately treated PEDOT:PSS as anode buffer layer exhibited significantly enhanced lifetime and decreased driving voltage. The results suggest that the appropriate mild oxygen plasma treatment of PEDOT:PSS layers may be useful for the improvement of the interface with the hole transport layer and enhanced device performance.

The thermodynamically stable conformation of a 25-residue segment drastically changes depending on the method to compute the solution effect: the stable conformations from explicit (left) and implicit (right) solvents.We compared effects of implicit (GB/SA) and explicit (TIP3P) solvents on physical quantities of a 25-residue polypeptide by performing multicanonical molecular dynamics simulations. To assess the effects systematically, we examined two intra-polypeptide force fields for each solvent model. The force fields have different secondary-structure propensities. We computed the temperature dependence of helix content, radius of gyration, end-to-end distance, and free-energy landscape. These physical quantities showed large differences between the two solvent models in each force field. For instance, the most thermodynamically stable conformation from the GB/SA solvent was an α-helix, although that from the TIP3P solvent was a β-sheet.

Distance information from proton-driven spin diffusion under MAS by Andreas Grommek; Beat H. Meier; Matthias Ernst (404-409).
The measurement of small dipolar couplings, corresponding to long internuclear distances, in the presence of large couplings is investigated for proton-driven spin-diffusion (PDSD) experiments in 13C solid-state magic-angle spinning NMR.The measurement of small dipolar couplings, corresponding to long internuclear distances, in the presence of large couplings is investigated for proton-driven spin-diffusion (PDSD) experiments in 13C solid-state magic-angle spinning NMR. Analytical calculations and numerical simulations using coherent and incoherent models as well as measurements on a model substance indicate that dipolar truncation, the suppression of polarization transfer across small couplings by larger ones, does not strongly influence the PDSD experiments. Therefore, long internuclear distances (>3 Å) corresponding to small dipolar couplings can be measured even in the presence of larger couplings. This finding holds promise for structure determination by solid-state NMR using uniformly labelled biomolecules.

Ab initio study of the toluene dimer by David M. Rogers; Jonathan D. Hirst; Edmond P.F. Lee; Timothy G. Wright (410-413).
Non-counterpoise-corrected MP2/6-31++G∗∗ optimized geometries of the three toluene dimers. The CCSD(T) energies suggest the energy ordering is unchanged, with the lowest-energy isomer on the left.We study different conformers of the toluene dimer using unconstrained geometry optimizations at the MP2 level of theory. We reoptimize these employing counterpoise-corrected MP2 gradients, and subsequently perform single-point counterpoise-corrected CCSD(T) interaction energy calculations. An antiparallel-stacked structure is found to be the most stable of the three isomers and has an interaction energy that is narrowly below that of a cross structure; a parallel-stacked structure is the least stable of the three isomers. We find no evidence for a stable T-shaped isomer, that is, no minimum on the potential energy surface corresponding to this structure.

Figure shows the free energy landscape of a type of lysozyme that has two folding pathways.By taking the ratio of Go-interaction parameters in two subdomains as an adjustable parameter, we found a variety of folding pathways for the proteins of same native topology.To elucidate the role of relative stability of subdomains in folding processes of multi-domain proteins, we have studied a free-energy landscape of c-type lysozyme by Monte Carlo simulations using a realistic lattice model with a Gō-like interaction. By varying the relative interaction strength of two subdomains as a parameter, we obtained a variety of the free-energy landscapes. Experimentally-observed diversity in folding processes of c-type lysozymes can then be described by this Gō-like model with only one variable parameter. The result demonstrates that folding of multi-domain proteins can be understood in the framework of the energy landscape theory.

Vindicating the Pauling-bond-order concept by Jelena Sedlar; Ivana Anđelić; Ivan Gutman; Damir Vukičević; Ante Graovac (418-420).
The Pauling-bond-order, in which the ith Kekulé structure has weight w i  = 1; i  = 1, 2, …,  K, is modified as w i = 1 + λ f i ; i = 1 , 2 , … , K with f i the number of Fries-type hexagons, and w i = 1 + λ g i ; i = 1 , 2 , … , K with g i  = 1 if the Kekulé structure is compatible with at least one Clar formula, and g i  = 0 otherwise. Improvements in reproducing experimental carbon–carbon bond lengths are insignificant.In the Pauling-bond-order concept, it is assumed that all Kekulé structures of a benzenoid molecule contribute equally to the π-electron contents of the carbon–carbon bonds. We modified the Pauling-bond-order: (a) by increasing the weight of a Kekulé structure proportional to the number of Fries-type hexagons and (b) by increasing the weights of the Kekulé structures that are compatible with Clar aromatic sextet formulas. Improvements in reproducing experimental carbon–carbon bond lengths are insignificant, implying that equal weighting of Kekulé structures is more justified than one could anticipate.

Nucleophilicity scale for n- and π-nucleophiles by Paula Jaramillo; Patricio Fuentealba; Patricia Pérez (421-425).
This figure show the comparison between logarithm of the rate constant (log  k) and the calculated nucleophilicity for phosphanes and phosphites. The calculated nucleophilicity indices are in agreement with the available experimental data.A recently introduced empirical nucleophilicity index for a series of n- and π-nucleophiles was evaluated. The index is based on the frontier molecular orbital information of the nucleophile and its electrophilic partner. The model is validated against kinetic data of alkenes, phosphanes, phosphites and amines interacting with the corresponding electrophilic partner. The predictive character of this index is tested for some nucleophiles.

Three-dimensional magnetization trajectories for a solution of water, acetone, and DMSO following a 150° pulse. Targeting differential spin control, the radiation damping feedback field was used to determine the three-dimensional magnetization trajectories of each spin species in this solution magnetic resonance experiment.In solution magnetic resonance (MR), manipulating the spin system in real time is difficult to implement in part due to the challenge of measuring the longitudinal magnetization within the constraints of MR detection hardware. Here we exploit the dynamical frequency shift induced by the radiation damping feedback field to estimate the longitudinal magnetization of individual spin species in one-, two-, and three-component spin systems. The calculated longitudinal magnetization is found to be in excellent agreement with that measured through independent experiments. Targeting the goal of differential spin control, extensions of this approach to real-time tracking of magnetization trajectories are discussed.

Metal-enhanced phosphorescence (MEP) by Yongxia Zhang; Kadir Aslan; Stuart N. Malyn; Chris D. Geddes (432-437).
Phosphorescence spectra of Rose Bengal immobilized in an organic glass between both silvered and unsilvered glass slides at 77 K with real-color photographs taken through an emission filter.We report the first observation of metal-enhanced phosphorescence (MEP) at low temperature. Silver island films (SiFs) in close proximity to Rose Bengal, significantly enhance the phosphorescence emission intensity. The enhanced phosphorescence intensity is ≈5-fold brighter from SiFs as compared to a glass control sample at 77 K. In addition, enhanced fluorescence emission and spectral narrowing were observed at low temperatures. Our findings suggest that both singlet and triplet states can couple to surface plasmons and enhance both fluorescence and phosphorescence yields. This finding suggests that MEP can be used to promote triplet-based assays, such as those used in photodynamic therapy.

The broken symmetry technique is used to determine the nature of the exchange coupling between the two paramagnetic centers of the BBDTA diradical. The coupling is found to large and antiferromagnetic. The broken symmetry wave function has a large, R BS, diradical character index.The broken symmetry (BS) solutions, obtained from various electronic structure calculations, are used to assign the ground state of the benzo-1,2:4,5-bis(1,3,2-dithiazolyl) molecule (BBDTA). In every case, the exchange between the BBDTA’s two 1,3,2-dithiazolyl paramagnetic centers is found to be antiferromagnetic leading to a singlet ground state. The Hartree–Fock values of the exchange parameter, J, are the smallest while the local density functional ones are the largest. As expected, the hybrid density functionals give intermediate values. The BS wavefunctions are also analyzed and Neese’s diradical character index, R BS, is found to range from 63.5% to 99.8%.

The optimized structures of the three tautomers (i.e., the enol, thiol and keto forms) for photo-induced tautomerism reaction (enol → keto) in the crystal. The proton is transferred along two different intermolecular hydrogen bonds by the effects of photoirradiation. The arrows mark the relevant proton.A novel keto–enol phototautomeric compound of 1-phenyl-3-methyl-4-(-furoyl)-5-pyrazolone 4-methyl thiosemicarbazone was found to undergo phototautomerization in the crystalline state. The reaction rate constant was studied based on the first-order kinetics curve. Crystal structural analysis and theoretical calculations show that the pyrazolone ring stabilizes in the keto form. The conclusion can be made that its phototautomerization in the crystalline state is associated with a photo-induced intermolecular double-proton-transfer reaction along intermolecular hydrogen bonds N―H⋯O and S⋯H―N leading to a colored tautomer as the compound crystallizes in a hydrogen bonded supramolecular configuration.

A DFT based ligand field study of the EPR spectra of Co(II) and Cu(II) porphyrins by Mihail Atanasov; Claude A. Daul; Marie-Madeleine Rohmer; Tamilmani Venkatachalam (449-454).
Using a DFT based Ligand Field treatment (LFDFT) of the electronic structure of Co(II) and Cu(II) porphyrins (CoP and CuP) we analyse the origin of their EPR spectra. It is found for CoP that the g-tensor values are very sensitive to the axial coordination which stabilizes a 2A1 ground state in good agreement with experimental data.Using a DFT based Ligand Field treatment (LFDFT) of the electronic structure of Co(II) and Cu(II) porphyrins (CoP and CuP) we analyse the origin of their EPR spectra. From a comparison between theoretical result on Co model clusters (CoP and CoP–ZnP dimer) we conclude that the g-tensor values are very sensitive to the axial coordination which stabilizes a 2A1 ground state in good agreement with experimental data. In contrast, DFT overestimates Cu–ligand covalency, leading to large discrepancy with experiments, and hence the orbital contribution to the computed g-values is too small. Using a numerical adjustment of nuclear charge for Cu, a good agreement between the computed and the experimental g-tensor values is observed. The influence of the DFT functional on the calculated g-tensor is also discussed.

A theoretical study on complete protonation of a series of tetrabasic molecules with general formula N[(CH2) n NH2][(CH2) m NH2][(CH2) p NH2] (tren, pee, ppe, tpt, epb and ppb) is reported. For first time, three kinds of gas-phase proton affinities for each polybasic molecule are defined as: ‘proton microaffinity (PA n,i )’, ‘proton macroaffinity ( PA ¯ n )’ and ‘proton overallaffinity ( PA ¯ ov )’.A theoretical study on complete protonation of a series of tetrabasic molecules with general formula N[(CH2) n NH2][(CH2) m NH2][(CH2) p NH2] (tren, pee, ppe, tpt, epb and ppb) is reported. For first time, three kinds of gas-phase proton affinities for each polybasic molecule are defined as: ‘proton microaffinity (PA n,i )’, ‘proton macroaffinity ( PA ¯ n ) ’ and ‘proton overall affinity ( PA ¯ ov )’. The variations of calculated log PA ¯ n in the series of these molecules is very similar to that of their measured log  K n . There is also a good correlation between the calculated gas-phase proton macroaffinities and proton overallaffinities with corresponding equilibrium macroconstants and overall protonation constants in solution.

Production of the radicals in the ozonolysis of ethene: A chamber study by FT-IR and PERCA by Bin Qi; Kei Sato; Takashi Imamura; Akinori Takami; Shiro Hatakeyama; Yan Ma (461-465).
The ozonolysis of ethene was investigated in a reaction chamber by in situ analysis of stable species by FTIR and of total peroxy radicals PO2 (PO2  = HO2  + RO2) by a chemical amplifier instrument. The yields of radical production were determined based on steady state concentrations of the peroxy radicals and the partitioning between HO2 and RO2 derived from model simulations.The ozonolysis of ethene in dry synthetic air at atmospheric pressure and room temperature (298 ± 2) K was investigated in a 6065-L reaction chamber by in situ analysis of stable species by FTIR and of total peroxy radicals PO2 (PO2  = HO2  + RO2) by a chemical amplifier instrument. The yields of radical production were determined based on steady state concentrations of the peroxy radicals and the partitioning between HO2 and RO2 derived from model simulations. The radical yield is 0.38 ± 0.02 for HO2 and 0.45 ± 0.03 for PO2.

Ab initio density functional theory for spin-polarized systems by Denis Bokhan; Rodney J. Bartlett (466-471).
Ab initio density functional method, based on second-order many-body perturbation theory has been generalized to spin-polarized open-shell systems. Results for energies and V xc are presented. Ab initio density functional method, based on second-order many-body perturbation theory has been generalized to apply to spin-polarized open-shell systems. Results for energies and V xc are presented.

Author Index (472-480).