Chemical Physics Letters (v.400, #4-6)

Oscillator strengths and transition probabilities for transitions among the fine-structure levels in Mg-like P IV, S V, Cl VI, and Ar VII are calculated within the weakest bound electronic potential model theory. Our results are discussed and compared with the calculations and experimental values. Oscillator strengths for 3 s 3 d 3 D J – 3 s 4 f 3 F J ′ 0 and 3 s 4 d 3 D J – 3 s 4 f 3 F J ′ 0 transitions, for which very few results exist, are also computed.

Conformational equilibria and photoinduced tautomerization in 2-(2′-pyridyl)pyrrole by Michał Kijak; Anna Zielińska; Charles Chamchoumis; Jerzy Herbich; Randolph P. Thummel; Jacek Waluk (279-285).
Depending on the polarity and protic abilities of the solvent, 2-(2′-pyridyl)pyrrole can exist in either syn or anti rotameric forms. In nonpolar solvents, intramolecular excited state single proton transfer is observed, manifested by the appearance of low-energy tautomeric emission. The solvent-assisted excited state double proton transfer reaction is also detected. DFT calculations confirm low barriers for both single and double proton transfer processes in the lowest excited singlet state and show different character of the tautomerization in both cases: in the intramolecular reaction, mutual approach of two nitrogen atoms plays an important role.

Crystal structure and spectroscopic properties of new fluoride compound Na2K2NdF7 by P. Solarz; A. Pietraszko; G. Dominiak-Dzik; W. Ryba-Romanowski (286-289).
New fluoride compound Na2K2NdF7 has been synthesised and obtained in the single crystal form by the Bridgman method. The crystal is cubic, space group Im 3 ¯ m , with lattice parameters a  = 1.28283 (15) nm. In this structure Nd3+ ions reside in sites with C 4v symmetry. Judd–Ofelt analysis of optical absorption spectra revealed that radiative lifetime of the 4F3/2 level of Nd3+ equals to 460 μs. Measured lifetime is 2.8 μs for Na2K2NdF7 and 439 μs for Na2K2La0.99Nd0.01F7, in agreement with the calculated value.

The influence of different substrates on the molecular orientation of organometallic polymer Pt-DEBP, [―Pt―(PBu3)2 ―CC―C12H8 ―CC―] n , has been investigated by NEXAFS spectroscopy. Thin films were deposited on HOPG, Au/Si(1 1 1), Cr/Si(1 1 1), Si(1 1 1) and stainless steel. The assignment of the spectral features has been carried out on the basis of previous STEX calculations performed on phenylacetylene model molecule in gas phase and adsorbed on Pt(1 1 1) and Cu(1 0 0). Angular dependent analysis of the π* resonance occurring at 285.50 eV photon energy deriving by the benzene carbon orbitals showed a polarisation effect for all substrates. A preferential molecular orientation at nearly 40° to the surface normal was observed. This result might be explained by the strong interaction between sp and sp2 carbons of the organic diethynylbiphenyl DEBP moiety contained in close chains, leading to polymer self-assembling.

Aggregation and micelle formation of ionic liquids in aqueous solution by Zsombor Miskolczy; Krisztina Sebők-Nagy; László Biczók; Sinem Göktürk (296-300).
Association of ionic liquids possessing n-octyl moiety either in the cation or in the anion has been studied in aqueous solution with conductivity and turbidity measurements as well as using 2-hydroxy-substituted Nile Red solvatochromic probe. 1-Butyl-3-methylimidazolium octyl sulfate was found to act as a surfactant above 0.031 M critical micelle concentration. In contrast, 1-methyl-3-octylimidazolium chloride produced inhomogeneous solution of larger aggregates, which were dissolved on the addition of more than 2:1 molar excess of sodium dodecyl sulfate (SDS) due to mixed micelle formation. Even small amount (<10 mM) of ionic liquids could markedly reduce the polarity of the Stern layer of SDS micelle.

Vibrational amplitude profile of molecular vibrational modes for vibrational mode assignment by Takayoshi Kobayashi; Masakatsu Hirasawa; Yuzo Sakazaki; Hiroki Hane (301-307).
Ultrashort pulse lasers with 6- and 20-fs durations were utilized for phthalocyanine thin film sample to induce several vibrational modes and vibration amplitude spectra were determined by multi-wavelength measurement technique. From the spectra we could identify the electronic states, which couple to two vibrational modes with frequencies of 670 and 750 cm−1. It was shown that the vibrational amplitude profile obtained by the method can be used for providing information for the assignment of the vibrational mode.

Multi-overlap molecular dynamics methods for biomolecular systems by Satoru G. Itoh; Yuko Okamoto (308-313).
We propose a molecular dynamics method for the multi-overlap algorithm. By utilizing a non-Boltzmann weight factor, this method realizes a random walk in the overlap space at a constant temperature and explores widely in the configurational space, where the overlap of a configuration with respect to a reference state is a measure for structural similarity. We can obtain detailed information about the free-energy landscape and the transition states among any specific reference conformations at that temperature. We also introduce a multi-dimensional extension of the multi-overlap algorithm. Appling this multi-dimensional method to a penta peptide, Met-enkephalin, we demonstrate its effectiveness.

We present a simple theoretical analysis of the DNA–DNA electrostatic interactions within charge-neutral lamellar cationic lipid/DNA complexes (lipoplexes). Although always repulsive as a function of the DNA–DNA interaxial distance, the calculated electrostatic force shows a deep minimum for each value of lipid composition corresponding to an equilibrium distance of the system. The excellent agreement between the equilibrium distances predicted by the model and that experimentally observed in charge-neutral complexes as revealed by synchrotron X-ray diffraction, shows that the spatial dimensionality of both the lipids and the DNA may not be a crucial point to capture the essence of the DNA–DNA interactions within charge-neutral lipoplexes.

Phase-shift cavity ring-down spectroscopy to determine absolute line intensities by J.H. van Helden; D.C. Schram; R. Engeln (320-325).
Cavity ring-down detection techniques can sensitively determine frequency-dependent absorption cross-sections of gasses. However, so-called line-width problems and amplified spontaneous emission of the laser light source lowers the technique’s quantitative accuracy. Using phase-shift cavity ring-down spectroscopy (PSCRD), we measured absolute line intensities of the spin-forbidden transitions in the b 1 Σ g + ( ν ′ = 0 ) ← X 3 Σ g - ( ν ″ = 0 ) band of molecular oxygen. Our results were within 4% of values obtained from the HITRAN database, demonstrating the accuracy of PSCRD, when corrected for amplified spontaneous emission. Its high sensitivity (2 × 10−8 cm−1), simplicity and high duty cycle make PSCRD a powerful diagnostic technique.

High-pressure Raman scattering experiments of O2 and N2 were carried out at 296 K and at pressures up to 10 and 6 GPa, respectively, and the pressure dependence of vibrational spectra of O2 was studied on the basis of molecular interactions in comparison with N2. An appreciable contribution of the attractive interaction to the vibrational frequency was observed for fluid O2. The linewidth of the spectra for fluid O2 showed a sharp increase with increasing pressure, and the fluid–solid transition was observed at 5.9 GPa with a sudden drop of the linewidth.

1.54 and 1.75 μm infrared luminescence of Y2O3:Er3+ by Xiao Xia Zhang; King Fai Li; Kok Wai Cheah; Xianju Zhou; Peter A. Tanner (331-335).
A new 1.75 μm infrared emission transition of Y2O3:Er3+ is assigned to the 4S3/2  →  4I9/2 transition of Er3+ ions situated at the C 2 sites of cubic RE2O3 (RE = Y, Gd, Lu). The intensities of features in the 1.54 μm 4I15/24I13/2 absorption transition due to Er3+ at S 6 and C 2 sites are consistent with the site occupation ratio and the relative magnetic dipole–electric dipole intensity contributions of Er3+ at the different sites. The 1.54 μm emission lines are predominantly from Er3+ ions at C 2 sites. The different behaviours of the emission intensities 1.75 and 1.54 μm groups with change in Er3+ dopant ion concentration, preparation technique, Yb3+ co-doping, temperature change and different excitation line are rationalized.

We have applied the elastic-scattering Green’s function theory to study the coherent electron transportation processes in both metal–alkanedithiol–metal (gold–[S(CH2) n S]–gold, n  = 8–14) and metal–alkanemonothiol–metal (gold–[H(CH2) n S]–gold, n  = 8–14) at the hybrid density functional theory level. It is shown that the current decreases exponentially with the molecular length. At the low temperature limit the electron decay rate, β, for alkanedithiol junction is found to be around 0.30/CH2 at 1.0 V bias, much smaller than the calculated value of 0.60/CH2 for alkanemonothiol junction. The decay rate for alkanedithiol junction at the room temperature is neither sensitive to the activation of the Au–S stretching vibrational mode nor to the external bias. The calculated current–voltage characteristics and decay rates for both junctions are in excellent agreement with the corresponding experimental results.

The G band in Raman spectra of single-wall carbon nanotube (SWNT) bundles is studied between 3 and 500 K. The G band is best fit with five Lorentzian lines and one Breit–Wigner–Fano (BWF) line, indicating coupling of phonons to the electronic continuum of metallic SWNTs. It is found that the line width of the BWF line decreases with increasing temperature. This temperature-dependent behavior is contrary to that of the Lorentzian lines, where the line width increases with increasing temperature. The coupling constant ∣1/q∣ of the BWF line is also found to decrease with increasing temperature. These temperature-dependent behaviors of BWF line provide evidence that it is the bundling effect of SWNTs that greatly enhances the BWF coupling.

Formation of π-coupled organic wire on the Si(0 0 1)[2 × 1] surface by Alain Rochefort; Alexandre Beausoleil (347-352).
The stability and electronic properties of highly packed 1-hexyl-naphthalene (HNap) molecular wire on Si(0 0 1) have been studied with first principles DFT method. HNap assembles into a 1D arrangement on the Si(0 0 1)[2 × 1] surface on which molcules adopt a commensurate structure along a dimer row with an intermolecular distance of 3.8 Å. HNap is attached to the surface through the hexyl chain, and stands normal to the surface. This highly packed structure leads to the formation of delocalized π-orbitals over the entire wire but essentially localized on the naphthalene counterpart, and well separated from the Si surface states. Cohesion energy within the wire arises from a significant attraction between hexyl chains, and to a weaker stabilizing π–π interaction between naphthalenes.

Grafting of chains organo-silane on silica surface: a quantum chemical investigation by A. Dkhissi; A. Estève; L. Jeloaica; D. Estève; M. Djafari Rouhani (353-356).
Theoretical calculations have been carried out on the grafting of two chains organo-silane compounds on SiO2 hydroxylated solid surfaces. Considering two different silylated coupling agents, two grafting stable complexes are obtained. These complexes are stabilized by two interactions: (i) the chain is grafted to the cluster with a covalent bond Si―O―Si; (ii) the chain interacts with the cluster via an hydrogen bond H―O⋯O in the other side of the chain. The electronic, geometrical and vibrational properties of these systems are analysed. These results give new insight about the grafting of long chains organo-silane on silica surfaces.

THz spectroscopic investigation of 2,4-dinitrotoluene by Yunqing Chen; Haibo Liu; Yanqing Deng; Dunja Schauki; Michael J. Fitch; Robert Osiander; Caroline Dodson; James B. Spicer; Michael Shur; X.-C. Zhang (357-361).
We have investigated the terahertz (THz) spectrum of 2,4-DNT by using Fourier transform infrared spectroscopy in the 0.2–19.5 THz region. We also examined low-frequency intermolecular or phonon modes between 0.2 and 1.8 THz via THz time-domain spectroscopy. The extracted absorption coefficient and refractive index of an intermolecular band at 1.08 THz are ∼110 cm−1 and 1.67, respectively. Density functional theory (DFT) was applied to obtain structure and vibrational frequencies of 2,4-DNT. The calculated results are in agreement with the experimental data. Observed vibrational frequencies have been interpreted using DFT. Two intermolecular or phonon modes were identified at 1.08 and 2.52 THz.

The substituent effect in ethylenes and acetylenes – AIM analysis by Sławomir J. Grabowski; Maciej A. Walczak; T. Marek Krygowski (362-367).
The calculations on disubstituted ethylenes YCH=CHX with Y = Li, H, F and X = H, F, Li, Na, OH, BeH, NH2, BH2, NO2 were performed at MP2/6-311++G(d,p) level of theory. The analysis of bond lengths and atoms in molecules based theory (AIM) topological parameters such as the characteristics of bond critical points (electron densities and their Laplacians) and atomic radii leads to the conclusion that the AIM parameters are much more sensitive to the action of intramolecular perturbations like substituents than traditional structural parameters such as bond lengths. A comparison of substituted ethylenes with the previously analyzed substituted acetylenes is also given.

The ultrafast dynamics of polybutadiene have been studied using ultrafast optical-Kerr-effect spectroscopy. The data are compared with measurements on 1,3- and 1,4-pentadiene. The two diene derivatives have quite distinct subpicosecond dynamics, with an important contribution from an intramolecular torsional mode in the 1,4-derivative. The main part of the polymer spectral density can be assigned, by analogy with the data for 1,4-pentadiene, to intramolecular torsional motion about carbon–carbon single bonds. The picosecond diffusive orientational relaxation times of the dienes are not well described by simple hydrodynamics.

Cavity ring-down spectroscopy (CRDS) has been applied to the detection of oxygen atoms, on the highly forbidden 1D2  ←  3P2 line at 630.030 nm. Results are presented for CRDS detection in a discharge flow system, in which the atoms are prepared by a microwave discharge of N2O/Ar or O2. Comparison of concentrations determined by CRDS and chemical titration by NO2 is made. CRDS is found to be a non-intrusive technique for the determination of oxygen atom concentrations in the range of 1014 atoms cm−3 and higher, with an estimated accuracy of ⩽20%.

Intra- and intermolecular fluorescence quenching in 7-(pyridyl)indoles by Gabriela Wiosna; Irina Petkova; Maria S. Mudadu; Randolph P. Thummel; Jacek Waluk (379-383).
Three isomeric 7-(pyridyl)indoles reveal very different, solvent-dependent photophysical properties. Due to rapid excited state depopulation involving intramolecular hydrogen bonding, 7-(2′-pyridyl)indole is practically nonfluorescent at room temperature. In nonpolar and polar aprotic solvents, 7-(3′-pyridyl)indole and 7-(4′-pyridyl)indole fluorescence strongly, but the emission is quenched in alcohols. Syn and anti rotameric forms of 7-(3′-pyridyl)indole are detected, each quenched to a different degree. This differential quenching is interpreted as evidence of enhanced S1  → S0 internal conversion being more efficient in cyclic solvates, with alcohol molecules forming a bridge between the proton donor and acceptor groups of an excited chromophore.

Electron transport properties of incommensurate double-walled carbon nanotubes by Jiangwei Chen; Linfeng Yang; Huatong Yang; Jinming Dong (384-388).
An efficient way is developed to calculate the matrix elements of Green’s functions in real space, by which conductances of the long clean incommensurate double-walled carbon nanotubes (DWNTs) are calculated. It is shown that, in a certain lower energy region, the conductances keep 2G 0 except for at a few energy positions for the system length at least up to about 1.4 μm, and when the tube length increasing to be 10 μm order, the conductance tend to be 1G 0, which is in good consistency with the experiments. The electron motion in the other higher energy regions becomes nonballistic.

Electrochemistry of perfluorinated fullerenes: the case of three isomers of C60F36 by Demis Paolucci; Francesco Paolucci; Massimo Marcaccio; Maurizio Carano; Roger Taylor (389-393).
The structurally similar T, C 1 and C 3 isomers of C60F36 show significant differences in electrochemical behaviour, the reduction potentials (vs. SCE) being 0.04, 0.07, and 0.12 V, respectively. The relative addend positions influence both the energetics of the first one-electron reduction of C60F36 and the stability of electrochemically generated C 60 F 36 • - . Thus whereas full reversibility of the first reduction is observed at scan rates as low as 0.5 V/s for C 3-C60F36, reversible peaks were obtained for T- and C 1-C60F36 only at scan rates ⩾50 V/s. The subsequent multi-electron reductions of C60F36 occur at more negative potentials, and are accompanied by irreversible loss of fluorides, analogous to the behaviour of other perfluorinated fullerenes.

A DFT study of the generation of interstellar species XN (X = Cl, and Br) activated by molecular sieve clusters by Yanli Zeng; Lingpeng Meng; Shijun Zheng; Maofa Ge; Dianxun Wang (394-400).
A cluster DFT (B3LYP) calculation study of ClN3 and BrN3 dissociation pathways catalyzed by molecular sieve is reported. A three-tetrahedral molecular sieve cluster (Al(OHSiH3)(OSiH3)(OH)2, called T3) has been chosen in this study. Triplet-state products ClN and BrN are more easily produced with T3 molecular sieve cluster. Although the potential energy surfaces with T3 molecular sieve cluster are similar with those without T3 molecular sieve cluster, the dissociation process of ClN3 and BrN3 with T3 molecular sieve cluster becomes easier, which can be attributed to smaller energy gaps from the ground state reactant to the intersystem crossing point.

Improvement of the charge imbalance caused by the use of a p-type silicon anode in an organic light-emitting diode by G.Z. Ran; Z.L. Wu; G.L. Ma; A.G. Xu; Y.P. Qiao; S.K. Wu; B.R. Yang; G.G. Qin (401-405).
An indium-tin oxide anode was replaced with a p-type silicon anode in a bilayer small-molecule organic light-emitting diode. As results, the current increased largely due to the enhanced hole injection and the higher conductivity of the Si anode; the luminous efficiency decreased significantly due to carrier-induced exciton quenching and the worse charge imbalance. Ultra-thin film of SiO2 grown on the silicon anode improved the luminous efficiency to a certain extent by restraining the hole injection; enhancing electron injection became more desired.

The adsorption of molecular oxygen at defective edge sites of zigzag and armchair graphite surfaces has been investigated by adopting cluster models in conjunction with density functional theory. Several different types of chemisorbed O2 species are identified. It was found that the defect edge sites exhibit the significant catalytic role toward the adsorption and activation of molecular oxygen. The O2 molecule is not only able to strongly bind to these edge sites, but the O–O bond strength is obviously weakened. Moreover, the calculated adsorption energy for O2 adsorbed on the clean graphite basal surface is fairly consistent with the weak interaction nature of O2 with the surface observed in the experiment, indicating one-layer cluster model is an effective way to study O2 adsorption on graphite surface in terms of accuracy and computational cost, which is in agreement with previous experience. Whereas, we note that the local detailed arrangement of edge carbon atoms can play an important effect on the adsorption of O2 on defect surfaces.

The 1s core-level absorption spectra of the sp3 bonded carbon (cubic and hexagonal polymorphs) and boron nitrides (zincblende and wurtzite polymorphs) were calculated using an ab initio pseudopotential plane wave method including the core-hole effects. A comprehensive comparison with the available experimental data shows that there exist characteristic features that can be used to spectroscopically identify the different polymorphs. The anisotropic characters of K-edge absorption spectra in hexagonal diamond and wurtzite boron nitride can provide additional phase specific signatures. The application of the spectroscopic fingerprinting method in the experimental identification of these metastable sp3 bonded phases is discussed.

Combined use of rotational spectroscopy and ab initio calculations at the MP2/6-311++G(d,p) level of theory shows that the complex formed between vinyl fluoride and hydrogen fluoride has a planar geometry in which HF forms a hydrogen bond to the F atom of vinyl fluoride. With ϕ  = the angle CF⋯H = 121.4° assumed from the ab initio calculation, the distance r(FH) = 1.892(14) Å and the angular deviation θ  = 18.7(15)° of the F⋯H–F nuclei from collinearity were obtained by fitting the principal moments of inertia of the two isotopomers C2H3F⋯HF and C2H3F⋯DF investigated.

The π → π* excited states of long linear polyenes studied by the CASCI-MRMP method by Yuki Kurashige; Haruyuki Nakano; Yoshihide Nakao; Kimihiko Hirao (425-429).
Multireference Møller–Plesset perturbation theory with complete active space configuration interaction (CASCI-MRMP) is applied to the study of the valence π → π* excited states of all-trans linear polyenes C2n H2n+2 (n  = 3–14). Our focus was to determine the nature of the four lowest-lying singlet excited states, 2 1 A g - , 1 1 B u + , 1 1 B u - and 3 1 A g - and their ordering. The ionic 1 1 B u + state is the lowest optically allowed excited state, while the covalent 2 1 A g - , 1 1 B u - and 3 1 A g - states are the optically forbidden states. Theory predicts that the 1 1 B u - state becomes lower than the 1 1 B u + state at n  ⩾ 7 and that the 3 1 A g - state also becomes lower than the 1 1 B u + state at n  ⩾ 11.

We show that, even when the atomic structure of a single-walled carbon nanotube does not have mirror symmetry perpendicular to the tubule axis, the electron diffraction patterns of the single-walled carbon nanotube always possess 2mm symmetry. We have also analyzed the contributions of higher order Bessel functions to the intensity distribution on the layer lines and found that (a) their contributions are negligible and (b) they would not affect the symmetry of the diffraction pattern. Both experimental and simulated electron diffraction patterns of a single-walled carbon nanotube of indices (14, 9) are presented to illustrate the 2mm symmetry and to corroborate the theoretical analysis.

In this study, we report the first sonoelectrochemical methods to prepare gold–silver alloy nanoparticles with the mean diameter of 5 nm in 0.1 N HCl aqueous solutions without addition of any stabilizer. First, a silver substrate was roughened by a triangular-wave oxidation–reduction cycle (ORC) in an aqueous containing 0.1 N HCl. Silver-containing complexes were found in the solution after the ORC treatment. Then a gold substrate was subsequently roughened by the similar ORC treatment in the same solution containing the silver complexes. After this procedure Au- and Ag-containing complexes were left in the solution. Then the Au working electrode was immediately replaced by a Pt electrode and a cathodic overpotential of 0.6 V from the open circuit potential (OCP) of ca. 0.75 V vs Ag/AgCl was applied under sonification to synthesize Au–Ag alloy nanoparticles.

On the triplet state of poly(N-vinylcarbazole) by J. Pina; J. Seixas de Melo; H.D. Burrows; A.P. Monkman; S. Navaratnam (441-445).
Triplet state properties including transient triplet absorption spectrum, intersystem crossing yields in solution at room temperature and phosphorescence spectra, quantum yields and lifetimes at low temperature as well as singlet oxygen yields were obtained for poly(N-vinylcarbazole) (PVK) in 2-methyl-tetrahydrofuran (2-MeTHF), cyclohexane or benzene. The results allow the determination of the energy value for the lowest lying triplet state and also show that triplet formation and deactivation is a minor route for relaxation of the lowest excited singlet state of PVK. In addition, they show the triplet state is at higher energy than reported heavy metal dopants used for electrophosphorescent devices, such that if this is used as a host it will not quench their luminescence.

A simple procedure for decreasing the statistical error associated with Monte Carlo integration of oscillatory functions is presented. The method uses available information about the integral of a similar oscillatory function to correlate the estimates of the positive and negative components of the integral. Numerical tests show that information guided noise reduction (IGNoR) leads to substantial decrease of the statistical error, allowing meaningful results to be obtained with a fraction of the cost required to attain similar precision from the raw Monte Carlo estimate.

Adsorption of pyridine on Lewis acid sites of microcrystalline γ-alumina was studied by quantum chemical cluster model approach at B3LYP and HF/6-31++G(d,p) levels of theory considering both the standard and the counterpoise-corrected potential energy surfaces (PESs). Harmonic vibrational frequency shifts of pyridine ν 8 and ν 19 internal mode components calculated at both levels of theory seem to excellently reproduce the experimental observations, the results for standard and counterpoise-corrected PESs being essentially identical. The interaction energies of pyridine with various clusters representing microcrystalline γ-Al2O3 were also calculated and the natural bond orbital and atoms in molecules analyses were performed.

The effective permittivity of binary mixtures having the spectral density function of the β distribution form is considered. Some particular cases such as low-concentration limit, weak and high dielectric contrast limit are considered in more detail. Finally, the validity of the approach for some microgeometries is supported by its good agreement with independent methods.

Optimal quantum control with multi-polarization fields by Rong Wu; Ignacio R. Sola; Herschel Rabitz (469-475).
The dynamical advantages for employing up to three independently shaped polarization fields are explored in the optimal control of quantum systems. The analysis compares multi-polarization optimal control with what may be achieved using linearly polarized (1-D) control. Simulations on model systems show how multi-polarization (2-D, 3-D) optimally shaped pulses can overcome symmetry forbidden transitions and improve control quality by better accessibility to the target state.

Low energy charge-transfer collisions of rare gas dications: Ne2+  + Ne and Kr2+  + Kr by O. Hadjar; D. Ascenzi; D. Bassi; P. Franceschi; M. Sabidò; P. Tosi (476-480).
We report measurements of the double charge transfer reactions Ne2+  + Ne → Ne + Ne2+ and Kr2+  + Kr → Kr + Kr2+ at hyperthermal energies. At collision energies below 0.8 eV, the experimental results are well reproduced by the capture (Langevin) cross section multiplied by the factor 1/2. For the single charge transfer channel, Ne2+  + Ne → Ne+  + Ne+, our experiment suggests that the process has a very small cross section.

The interaction of H2, CO, CO2, H2O and NH3 on ZnO surfaces: an Oniom Study by João Batista Lopes Martins; Elson Longo; Octavio D. Rodrı́guez Salmon; Vicente A.A. Espinoza; Carlton A. Taft (481-486).
We have used the Oniom method with three layers in order to study the interaction of CO, H2, H2O, NH3 and CO2 molecules with the ZnO ( 1 0 1 ¯ 0 ) surfaces using a (ZnO)348 cluster model. The layers are divided into the high layer at the CCSD level, the medium layer at the RHF level and the low level layer using the UFF force field method. The orbital and binding energies of the adsorbed molecules, Mulliken and ChelpG charges as well as geometrical parameters were analyzed and compared with the available experimental and theoretical data.

The degenerate properties of modified purine and pyrimidine DNA bases: a density functional study by Shenna M. LaPointe; Craig A. Wheaton; Stacey D. Wetmore (487-493).
Density-functional theory was used to study the properties (binding geometries and affinities for the natural DNA bases) of various degenerate nucleobases, which bind without discrimination to the purines or pyrimidines. The data for purine mimics (Z and K) indicates that although stronger binding strengths are calculated for pairs with cytosine compared with thymine, cytosine binds to a less stable tautomer of the nucleobase mimic. Indeed, the energy differences between the binding strengths and the tautomers effectively cancel and thereby provide a possible explanation for the observed degenerate properties of these molecules. Similar trends are found for the pyrimidine mimics (M and P); however, the energy differences do not cancel, even upon inclusion of environmental effects.

Relative strength of hydrogen bond interaction in alcohol–water complexes by Eudes E. Fileti; Puspitapallab Chaudhuri; Sylvio Canuto (494-499).
Hydrogen binding energies are calculated for the different isomers of 1:1 complexes of methanol, ethanol and water using ab initio methods from MP2 to CCSD(T). Zero-point energy vibration and counterpoise corrections are considered and electron correlation effects are analyzed. In methanol–water and ethanol–water the most stable heterodimer is the one where the water plays the role of proton donor. In methanol–ethanol the two isomers have essentially the same energy and no favorite heterodimer could be discerned. The interplay between the relative binding energy is briefly discussed in conjunction with the incomplete mixing of alcohol–water systems.

Characteristic near-field spectra of single gold nanoparticles by Kohei Imura; Tetsuhiko Nagahara; Hiromi Okamoto (500-505).
We investigate the interaction between evanescent wave and a single gold nanoparticle in near-field by utilizing an aperture-probe scanning near-field optical microscope. A characteristic spectral feature, consisting of transmission enhancement and absorptive parts, is found. Observed spectra are successfully simulated both by a model calculation based on extended Mie scattering theory of the near- and far-field scatterings as well as by a Green’s dyadic method.

Biological nano-ceramic materials for holographic data storage by Pengfei Wu; Murty Bhamidipati; Melissa Coles; D.V.G.L.N. Rao (506-510).
New Retinal nano-ceramic materials with pillared hybrid micro-structures are fabricated for potential applications in optical holographic data storage. We observe that the Schiff bases have substantial effect on optical properties of Retinal nano-ceramic films as well as temporal response and diffraction efficiency for holographic storage. These inexpensive synthetic biological nano-ceramic thin films are good candidates for holographic storage and offer a simple procedure to solve the problems of volatility of optical storage in Retinal proteins. In addition, our study indicates feasibility of optimizing optical properties of nano-ceramic clay systems using Schiff bases for a variety of photonic applications.

Transformation of ice in aqueous KCl solution to a high-pressure, low-temperature phase by Yukihiro Yoshimura; Ho-kwang Mao; Russell J. Hemley (511-514).
The changes in in situ Raman spectra of ice in aqueous KCl solution have been measured as a function of pressure at liquid nitrogen temperature (77 K). The ice that is formed abruptly transforms to a crystalline phase at ∼800 MPa. It has a spectrum close to that of ice VII′ to which high density amorphous (hda) ice transforms at about 4 GPa. This behavior contrasts with that of the ice in aqueous LiCl solution, which transforms to an amorphous phase at ∼500 MPa, as in the case of pressure-induced amorphization of ice I h to hda.

We have calculated the potential of mean force (PMF) for the transfer of a solute molecule across a liquid–vapour interface for four different systems: (a) one methanol molecule in water, (b) one water molecule in methanol, (c) one acetonitrile molecule in water and (d) one water molecule in acetonitrile by means of constrained molecular dynamics simulations. A minimum of the PMF is found near the Gibbs dividing surface for methanol and acetonitrile solutes although the degree of surface activity is found to be somewhat different due, in part, to varying hydrogen bonding nature of these two solutes.

Highly efficient Pt/TiO2 photocatalyst prepared by plasma-enhanced impregnation method by Ji-Jun Zou; Chang-Jun Liu; Kai-Lu Yu; Dang-Guo Cheng; Yue-Ping Zhang; Fei He; Hai-Yan Du; Lan Cui (520-523).
Highly efficient Pt/TiO2 photocatalyst has been prepared using plasma-enhanced impregnation method. Impregnated 0.5 wt%Pt/TiO2 was treated by plasma followed with thermal calcinations and hydrogen reduction. The catalyst characterizations show that Pt is highly dispersed with a size of 3–5 nm. UV–Vis reflection spectrum suggests it a high photosensitivity in near UV region. Such plasma prepared catalyst exhibits a much higher activity and better metal stability for hydrogen generation from methanol/water mixture, compared to the catalyst prepared conventionally. This highly efficient photocatalyst should have extensive applications in photocatalytic processes.

The influences of the electrostatic environment on the mechanisms of generation of rotational strengths in near-UV of β-lactamase TEM-1 are studied in two aspects: the first is the effects of ionized tyrosine chromophores and the second – the effects of the changes of the excitation energies of the chromophores under the local electrostatic interactions. The mechanisms of generation of rotational strengths by tyrosinate chromophores are described. It is shown that both effects (tyrosine ionizations and Coulomb interactions) influence the mechanisms of rotational strengths and the relative contributions of the chromophores in the near-UV.

The action spectrum of tetracene photooxygenation was measured in air-saturated carbon tetrachloride in the wavelength range of 1220–1290 nm using a wavelength-tunable forsterite laser. The data show that the photoreaction occurs due to laser excitation of the 1 Δ g ( ν = 0 ) ← 3 Σ g - ( ν = 0 ) transition in oxygen molecules. The molar absorption coefficient (ϵ 1273) and the cross section of light absorption (σ 1273) corresponding to the spectral maximum of this transition were calculated from the observed photoreaction rates. The obtained values ε 1273  = 0.003 M−1 cm−1 and σ 1273  = 10−23 cm2 (±20%) reasonably correlate with those extrapolated from the high-pressure oxygen absorption spectra.

Hexaniobate nanotubes with variable interlayer spacings by Gaohui Du; Yuan Yu; Lian-Mao Peng (536-540).
The novel hexaniobate nanotubes with variable interlayer spacings have been prepared via intercalating–exfoliating–rolling mechanism at the room temperature. The hexaniobate nanotubes are single crystalline with multiple walls. A few single-wall nanotubes have been observed also. The interlayer spacings of 0.83, 1.9, 2.2, 2.3, 2.4, 2.5, 2.8, 3.3 and 3.6 nm are, respectively, obtained by the intercalation of a series of primary alkylamines. The formation mechanism is discussed in detail and this method is applicable to other layered structure materials. These hexaniobate nanotubes are inorganic/organic composite and therefore represent a new class of tubular materials.

In this Letter, the interface geometry of silver thin films of thickness T between 1 and 3 ML epitaxially deposited at the MgO surface has been accurately characterized employing DFT periodic calculations. The Ag–Ag out-of-plane interlayer spacing is considerably shorter than the bulk values because of: (i) the reduced dimension; (ii) the perfect epitaxy constraint; (iii) the interaction with the substrate. The interface distance between the silver monolayer and the MgO substrate, d(Ag–O) = 2.60 Å, is considerably longer than the estimates computed for the bilayer and the trilayer, d(Ag–O) = 2.47 and 2.48 Å, respectively. The difference between the values of the interface distance computed for the monolayer and the results obtained for thicker films, lies in the peculiar electronic properties of the silver monolayer.

We have found a (dense) basis for the N-representable, two-electron densities, in which all N-representable two-electron densities can be expanded, using positive coefficients. The inverse problem of finding a representative wavefunction, giving a prescribed two-electron density, has also been solved. The two-electron densities are found to lie in a convex set in a vector space. An algorithm to compute the ground-state energy of a few-particle system is proposed, based on the obtained results.

In this Letter, we report the structural and luminescent properties of Tb:Ce:Al2O3 crystalline ceramic powders prepared through combustion synthesis at low temperature (∼280 °C). The presence of Ce3+ (1.0 mol%) in the sample resulted in an enhancement of Tb3+ (1.0 mol%) overall emission intensity by a factor of ∼50. The analysis of the luminescence dynamics for the 5D4  →  7F6 transition (∼545 nm) of Tb3+ demonstrated that the mechanism responsible for the large enhancement of luminescence observed is efficient energy transfer from Ce3+ to Tb3+.

Computational study of lithioprismanes by Igor Novak; Lawrence M. Pratt (558-562).
The molecular structure and thermochemical stability of mono to hexalithiated [3]-prismanes has been investigated by DFT and G3 methods, respectively. Relative isomer stabilities, standard enthalpies of formation and strain energies are discussed and compared. Our results suggest that in lithioprismanes (as in the isomeric lithiobenzenes), Li atom prefers to be in a bridging position along the CC edge rather than to occupy a vertex substitution site. We have estimated the energy stabilization due to bridging and have also studied singlet–triplet energy gaps for the title molecules in order to establish the nature of the ground electronic state.

The rate constants, k 1 and k 2 for the reactions of C2F5OC(O)H and n-C3F7OC(O)H with OH radicals were measured using an FT-IR technique at 253–328 K. k 1 and k 2 were determined as (9.24 ± 1.33) × 10−13 exp[−(1230 ± 40)/T] and (1.41 ± 0.26) × 10−12 exp[−(1260 ± 50)/T] cm3  molecule−1  s−1. The random errors reported are ±2 σ, and potential systematic errors of 10% could add to the k 1 and k 2. The atmospheric lifetimes of C2F5OC(O)H and n-C3F7OC(O)H with respect to reaction with OH radicals were estimated at 3.6 and 2.6 years, respectively.

The nonlinear transmittance of a novel hyperbranched conjugated polymer named DMA-HPV has been measured in CHCl3 solution using a nanosecond optical parametric oscillator. DMA-HPV shows excellent optical limiting performance in the visible region from 490 to 610 nm. An explanation based on the combination of two-photon absorption and reverse saturable absorption was proposed for its huge and broadband nonlinear optical absorption.

Sub-picosecond laser pulse driven localization of electronic excitation energy is suggested for a biological chromophore complex. Based on an exciton model of the photosynthetic core antenna PS1 of Synechococcus elongatus the shape of the respective laser pulse is calculated using optimal control theory combined with a density matrix theory accounting for energy relaxation and dephasing caused by the protein environment. As a target observable we choose the population oscillation after photo-excitation between the two Chlorophylls forming the special pair. The temperature dependence of the related control yield is studied as well as its dependence on the pulses duration.

We have investigated the electrochemical genosensing properties of gold nanoparticle–carbon nanotube hybrid. Thiolated oligonucleotide probes and mercaptohexanol were self-assembled onto the Au–CNT hybrid. The hybridization events of target oligonucleotides are monitored using electrochemical impedance spectroscopy, cyclic voltammetry and a.c. voltammetry techniques. A redox-active mediator Ru ( bpy ) 3 2 + is used to detect the oxidation of guanine residues. The as-fabricated genosensor is able to differentiate between complementary and mismatched hybridizations, relying on the oxidation current of the guanine residues mediated via Ru ( bpy ) 3 2 + .

Author index (583-592).