Chemical Physics Letters (v.447, #4-6)

Contents (iii-xiii).

Geometry structure and two typical band structures for H-terminated boron nitride nanoribbon (BNNR) with armchair and zigzag shaped edge.Structural and electronic properties have been studied for Boron Nitride nanoribbons (BNNR) with both zigzag and armchair shaped edge (Z-BNNR and A-BNNR) by first-principle spin-polarized total energy calculations. We found that the energy band gap of Z-BNNR is indirect and decreases monotonically with the increasing ribbon width, whereas direct energy band gap oscillation was observed for A-BNNRs. Additionally, C-substitution at either single boron or nitrogen atom site in BNNRs could induce spontaneous magnetization. Our results could be potentially useful to design magnetic nano-devices based on BNNRs.

Investigation of CD effects in the multi photon ionisation of R-(+)-3-methylcyclopentanone by Alexander Bornschlegl; Christoph Logé; Ulrich Boesl (187-191).
Resonance enhanced multi photon ionisation (MPI) allows to combine electronic CD spectroscopy and time-of-flight mass spectrometry by using circularly polarised laser light. Different MPI-excitation schemes have been investigated. New CD effects have been observed comparing one- and two-colour experiments.The circular dichroism (CD) in ion yield for different excitation/ionisation schemes for R-(+)-3-methylcyclopentanone was measured with circular dichroism laser mass spectrometry (CD-LAMS). We discovered a cumulative CD effect of successive electronic transitions, resulting in an enhancement of the CD in ion yield. Two photon excitation of the n–π-transition compared with the one photon process showed a vanishing CD effect.

The highly disordered relationship between potential at C para in the benzene ring and charge of the substituent turns into good linear one when charge of the substituent active region is considered instead.The Letter investigates correlations between substituent charges and electrostatic properties of C atoms in the ring, as well as between the charges and Hammett constants. It appeared that the substituent charges are uncorrelated with the mentioned data sets. A new variable, however, composed of charges of substituents added to charges of the C ipso atoms, proved to be highly correlated with these data sets. On that basis it has been found that notion of substituent active region, which comprises the substituent itself and the ring ipso carbon atom, recently introduced while investigating a group of p-substituted benzoic acids, also plays a part in the group of monosubstituted benzenes.

Observation of vibronic emission spectra of jet-cooled 2,3-difluorobenzyl radical in a corona excited supersonic expansion.We report the spectroscopic observation of difluorobenzyl radical in a corona excited supersonic expansion using a pinhole-type glass nozzle. A jet-cooled 2,3-difluorobenzyl radical was generated and vibronically excited from 2,3-difluorotoluene seeded in a large amount of inert carrier gas He. The vibronic emission spectra of the jet-cooled 2,3-difluorobenzyl radical were recorded for the first time in the visible region and analyzed to obtain an accurate measurement of the vibronic transition energy between the D1 and D0 electronic states. The vibrational mode frequencies in the ground electronic state were determined by comparison with those from an ab initio calculation as well as those of 2,6-difluorobenzyl radical and 1,2,3-trimethylbenzene.

A jet-cooled infrared spectrum of formic acid dimer in the C–O stretching region. The low rotational temperature attained in the jet enabled us to observe three vibrational bands which are not resolved at room temperature (upper trace).A jet-cooled infrared spectrum of the formic acid dimer (HCOOH)2 (FAD) has been measured by cavity ring-down spectroscopy in the C–O stretching region at 8 μm. The low rotational temperature in the jet enabled us to observe three vibrational bands which are not resolved at room temperature. The three bands have been interpreted as the Fermi-triad system which consists of the ν 22 fundamental band and two combination bands. An analysis of the observed rotational contours led us to the first experimental determination of anharmonic force constants for FAD.

Theoretical prediction of the formation of complexes between s-block metal ions and dihydrogen molecules, MH16, is reported. The number of hydrogen molecules attached to the metal cation is the highest ever known in the literature.Theoretical prediction of the formation of hydrogen-rich complexes of s-block metal ions and dihydrogen molecules, MH16, (M = Li1+, Na1+, K1+, Be2+, Ca2+, and Mg2+) is reported. The number of hydrogen molecules attached to the metal cation is the highest ever reported in the literature. The interaction between s-block metal ions and hydrogen is found to be weak and the binding energy calculated by MP2 method using cc-pVDZ basis set is observed to be of the order of −30 to −13.5 kcal/mol and −180 to −60 kcal/mol for alkali and alkaline earth metal cations, respectively. Using this simple ion–molecule interaction, the possibility of the application of these complexes for developing hydrogen storage materials is discussed.

Improved theoretical calculations of InN in its X3Σ ground state and in the first 3Π excited state by Lukáš Demovič; Ivan Černušák; Giannoula Theodorakopoulos; Ioannis D. Petsalakis; Miroslav Urban (215-220).
Spectroscopic constants of the ground and the first excited state of InN are calculated using CCSD(T), CASPT2, CASPT2/RASSI-SO, and MRCI methods.Spectroscopic constants of the two lowest states of the InN molecule, the X3Σ ground and the 3Π excited state were calculated using the restricted open-shell Hartree–Fock Coupled Cluster ROHF-CCSD(T) method with single, double and perturbative triples, the complete active space second-order perturbation theory (CASPT2) and the multireference configuration interaction (MRDCI) methods. Relativistic pseudopotentials (for MRDCI) and atomic natural orbital basis set for treating spin–orbit and scalar relativistic effects – ANO-RCC (for CCSD(T), CASPT2 and CASPT2/RASSI-SO) were used. The accuracy of different methods was compared correlating up to 26 valence and core-valence electrons of N and In atoms.

Vibrational amplitude change after 6.7 fs pulse excitation taking place in a quinoid thiophene was observed within two picoseconds.Several vibrational modes impulsively excited by 6.7 fs pulses were observed in a quinoid thiophene. From the amplitude decay time and the phase of vibration, the modulation mechanism of the electronic transition by the wave packet motion is discussed and classified in terms of vibronic coupling. Modes with wavenumbers of 1343 and 1420 cm−1 are attributed to the wave packet motions on the potential surface of the excited and ground state, respectively, and a mode with 1539 cm−1 is due to those of both states. The apparent low-frequency modulation of these three modes is ascribed to the artificial interference effect in the calculation of the spectrogram.

Charge transfer dynamics in self-assembled monomolecular films by S. Neppl; U. Bauer; D. Menzel; P. Feulner; A. Shaporenko; M. Zharnikov; P. Kao; D.L. Allara (227-231).
Femtosecond electron transfer dynamics in highly ordered self-assembled monolayers of nitrile-terminated alkanethiols is investigated using resonant Auger spectroscopy.Whereas static conductance of molecules arranged in self-assembled monolayers has been extensively studied, little is known about the dynamics of the charge transfer in these systems. By the example of alkanethiolate films, we show that the latter phenomena can be successfully addressed by resonant Auger spectroscopy, using the core hole clock method. The charge transfer pathway was unambiguously defined by resonant excitation of the nitrile tailgroup attached to the alkyl backbone. Extension of this approach to other functional groups is possible, leading to new information valuable for molecular electronics and other applications.

Nuclear spin conversion of water diluted in solid argon at 4.2 K: Environment and atmospheric impurities effects by L. Abouaf-Marguin; A.-M. Vasserot; C. Pardanaud; X. Michaut (232-235).
We show that the NSC of H2O diluted in solid argon is due to an enhancement of intramolecular spin–rotation coupling by solid argon environment.We have investigated the nuclear spin conversion of H2O in solid argon. At 4.2 K and for high dilution, we have measured a limit time of 680 ± 30 min. We have not observed any change of the conversion time upon double doping with CO2, CO, N2 and O2. No effect could be detected due either to the spectrometer light, the golden mirror surface or the crystalline quality of the matrix. Therefore, we can conclude that this time is only due to the interaction with the matrix, which may enhance nuclear spin conversion induced by intramolecular spin–rotation coupling.

The isochoric heat capacity of a metastable Lennard-Jones fluid by V.G. Baidakov; S.P. Protsenko; Z.R. Kozlova (236-240).
The isochoric heat capacity of the fluid passes through a minimum and continues to increase when approaching the spinodal (dashed-dotted lines).The article presents the results of molecular-dynamics calculations of the isochoric heat capacity, c v , and the (p,  ρ,  T) – properties of the Lennard-Jones fluid in the region of liquid–gas phase transition in stable and metastable states. The system under investigation contains 2048 particles, the cut-off radius of the potential is chosen equal to 6.78σ. The results of computations of the (p,  ρ,  T) – properties have been used to approximate the location of the spinodal. Values of c v have been determined along the gas and the liquid branches of the spinodal. A thermodynamic relation that determines the value of c v on the spinodal in terms of derivatives with respect to temperature of the entropy, pressure and specific volume along the spinodal has been obtained. It is shown that molecular-dynamics data are in agreement with the results of the thermodynamic analysis.

Absorption spectra showing the light-mediated 1,4-benzoquinone–bromine reaction, which leads to the production of bromated 1,4-hydroquinones.The 1,4-benzoquinone–bromine photoreaction is investigated with UV/Vis spectroscopy, mass spectrometry, and 1H NMR methods. The absorption and mass spectra suggest that 1,4-benzoquinone in aqueous solution reacts with bromine only in the presence of light, which leads to the production of brominated-1,4-hydroquinones. Parallel experiments performed with illuminated and unilluminated 1,4-hydroquinone–bromine reactions indicate that the bromination of the benzene ring takes place during rather than after the photoreduction of 1,4-benzoquinone. The results provide an explanation for the subtle photosensitivity seen in a number of acidic bromate–aromatic compound reactions.

Association with chloride or perchlorate anions leads to considerable change in the fluorescence properties of berberine, a cationic isoquinoline alkaloid.Effect of association with chloride or perchlorate anions on the fluorescence properties of berberine, a cationic isoquinoline alkaloid, has been studied. Interaction with Cl caused more efficient fluorescence quenching; it significantly accelerated the radiationless deactivation and slowed down the radiative transition. Combined analysis of spectrophotometric, steady-state and time-resolved fluorescence results provided 1.5 × 105  M−1 for the equilibrium constant of ion pairing with Cl in CH2Cl2. Both ion pairing and enrichment of the microenvironment of berberine in ions led to excited state quenching in solvents of medium polarity, but only the latter effect was observed in the presence of perchlorates in butyronitrile.

Radiation damage and Raman vibrational modes of single-walled carbon nanotubes by U. Ritter; P. Scharff; O.P. Dmytrenko; N.P. Kulish; Yu.I. Prylutskyy; N.M. Belyi; V.A. Gubanov; L.A. Komarova; S.V. Lizunova; V.V. Shlapatskaya; H. Bernas (252-256).
Raman scattering for the radial and tangential vibrational modes of single-walled carbon nanotubes (CNT) with different absorption doses of high-energy electron irradiation were explored. New vibrational modes both for the armchair and zigzag CNT appear and a substantial change in the intensities and broadening are observed for the high-frequency Raman bands with high absorption doses.We report on the behavior of Raman scattering for the radial and tangential vibrational modes of single-walled carbon nanotubes (CNT) with different absorption doses of high-energy electron irradiation (E e  = 1.8 MeV). We find that the atomic displacement of carbon from the CNT walls leads to the decrease of their diameter. In the case of the tangential optical vibrations the translational symmetry of CNT breaks down because of the radiation defects. Thus, new vibrational modes both for the armchair and zigzag CNT appear. Substantial changes in the intensities and broadening are observed for the high-frequency Raman bands with a 1.0 MGy absorption dose.

Effect of incident fluence on the growth of ZnO nanorods by pulsed excimer laser deposition by Ye Sun; Rachel P. Doherty; James L. Warren; Michael N.R. Ashfold (257-262).
The role of incident fluence upon the morphology of ZnO nanorod arrays grown by pulsed UV laser deposition is demonstrated and rationalised.The incident fluence is shown to be an effective parameter in controlling the diameters of ZnO nanorods grown by pulsed excimer laser deposition following ablation of a ZnO target in low background pressures of oxygen. The evolution in nanorod diameter and the overall sample morphology with incident fluence is rationalised by considering the bombardment effect of high energy species in the plume formed in the ablation event.

Isosurfaces of the squared wave function for the lowest unoccupied states of the (11, 0) nanotubes with the adatom–vacancy defects of which configuration are symmetric and asymmetric to the tube axis. In the asymmetric defect, the states exhibit extended character compared with the symmetric one.We report first-principle total-energy electronic-structure calculations in the density functional theory performed for carbon nanotubes with a defect consisting of a pair of an adatom and a vacancy. We find that the activation barriers for formation and healing of the defect are ∼10 and 2 eV, respectively, indicating the possibility of defect healing under moderate conditions. The defect is found to induce two gap states with characteristics that strongly depend on its arrangement. Further, the metal–insulator transition takes place on the (9, 0) nanotube owing to the formation of gap states.

Enhancement of electron–electron interactions in chemically synthesized polymer nanowires by Atikur Rahman; Milan K. Sanyal; Rupali Gangopadhayy; Amitabha De (268-273).
Electronic transport properties of conducting polymer nanowires synthesized by chemical and electrochemical method show power-law current–voltage characteristics at low temperature. Large value of the power-law exponent indicates enhancement of electron–electron interactions in chemically synthesized nanowires.We report here a comparison of electronic transport properties of conducting polymer nanowires synthesized by chemical and electrochemical methods inside nanopores. Electronic transport properties of these nanowires show a power-law behavior (I  ∝  V 1+β ) at low temperature. Chemically synthesized nanowires exhibit higher values of β and these values increase further with the diameter of nanowires. Zero bias differential conductance of all the nanowires increase with increasing diameter and temperature but the obtained values of chemically synthesized nanowires were always found to be much lower. These results indicate enhancement of electron–electron interactions in chemically synthesized nanowires.

Femtosecond and nanosecond nonlinear optical properties of alkyl phthalocyanines studied using Z-scan technique by R. Sai Santosh Kumar; S. Venugopal Rao; L. Giribabu; D. Narayana Rao (274-278).
We report strong nonlinear absorption properties of alkyl phthalocyanines studied using Z-scan technique with 800 nm femtosecond and 532 nm nanosecond pulses.We report our results on nonlinear optical properties of 2(3), 9(10), 16(17), 23(24) tetra tert-butyl phthalocyanine and 2(3), 9(10), 16(17), 23(24) tetra tert-butyl Zinc phthalocyanine studied using Z-scan technique with 800 nm femtosecond and 532 nm nanosecond pulses. Nonlinear absorption behavior in both femtosecond and nanosecond domains was studied in detail. We observed three-photon absorption with femtosecond laser excitation and strong reverse saturable absorption with nanosecond pulse excitation. We have also evaluated the sign and magnitude of the third-order nonlinearity.

Electro-photoluminescence in organics by J. Kalinowski; M. Cocchi; D. Virgili; V. Fattori; J.A.G. Williams (279-283).
A successful observation of the steady-state electro-photoluminescence (EL-PL) is reported in thin, exciplex emitting, organic solid films. It shows up as either an enhancement or quenching of the PL output, dependent on the electric field applied and light excitation intensity.We report a successful observation of the electro-photoluminescence (EL-PL) in thin, exciplex emitting, organic, solid films. The increasing electric field applied to injecting electrodes tends to reduce the total light emission because of the dissociation of emissive exciplex states and their precursors, and, at the same time, the radiative recombination of injected holes and electrons enhances the output of the electroluminescence (EL), the process that suppresses the total luminescence quenching. Increasing bulk concentration of the charge leads the EL output to exceed the PL component, a negative quenching (enhancement of the total emission) is observed.

An artificial supramolecular photosynthetic unit by Martin Katterle; Valentyn I. Prokhorenko; Alfred R. Holzwarth; Aldo Jesorka (284-288).
A self-assembled antenna mimics the supramolecular light-harvesting structure and an embedded dyad acts both as energy acceptor and charge transfer dyad.A biomimetic light harvesting and energy conversion unit is constructed by a modular self-organization methodology. A self-assembled antenna aggregate mimics the supramolecular light-harvesting structures of phototrophic bacteria, and an embedded reaction center model acts both as an energy acceptor and a charge transfer dyad. This unit can be viewed as a conceptual approach to self-assembled supramolecular solar cells, utilizing bio-inspired materials as a starting point for advanced solar energy conversion units.

OOH dissociation on Pt clusters by Yuguang Ma; Perla B. Balbuena (289-294).
Activation barriers for O–O dissociation on the cluster edges are reduced in one order of magnitude respect to those on the center of the cluster.OOH dissociation on Pt2, Pt3, Pt4, Pt7 and Pt12 clusters is studied using density functional theory. The activation energy varies widely with the size and geometry of the clusters, from 2.23 kcal/mol for Pt2 to 13.9 kcal/mol for Pt12. Calculations on a single-layer Pt12 used to emulate surface, edge, and corners of Pt(1 1 1) nanoparticles reveal that the energy barrier depends significantly on the adsorbate position on the cluster. The edge adsorption sites exhibit the highest catalytic activity. A correlation between the activation energy and the Pt–Pt distance suggests that the dissociation reaction can be facilitated by increasing the Pt–Pt distance.

Magnetic properties of dense carbon nanospheres prepared by chemical vapor deposition by José M. Calderón-Moreno; Amílcar Labarta; Xavier Batlle; Trinitat Pradell; Daniel Crespo; Vu Thien Binh (295-299).
Paramagnetic carbon nanospheres: The stable paramagnetic spins are located inside the solid carbon, at interfaces between graphitic-amorphous clusters.Carbon nanospheres (∅ ∼ 50 nm) prepared by chemical vapor deposition exhibit Curie-type paramagnetism, with a localized spin density N S  = 4.01 × 1019  spins/g. The spheres are solid, as shown by their cross-sections. Their low surface area excludes the presence of exposed graphene layers at the surface being the origin of paramagnetic centers. Inside the carbon spheres, HRTEM reveals a concentric wavy pattern of graphitic (sp2-bonded) clusters (size < 2 nm) embedded in disordered carbon. The high density of carbon atoms with sp2–sp3 hybrid orbitals acting as paramagnetic centers, at interfaces between graphitic (sp2-bonded carbon) clusters and amorphous carbon, can explain the magnetic measurements.

A two-photon absorption study of fluorene and carbazole derivatives. The role of the central core and the solvent polarity by I. Fitilis; M. Fakis; I. Polyzos; V. Giannetas; P. Persephonis; P. Vellis; J. Mikroyannidis (300-304).
The role of the central core and the solvent polarity on two-photon absorption of fluorene and carbazole derivatives is studied.The two-photon absorption (TPA) properties of a series of symmetrical fluorene and carbazole derivatives have been studied to determine the role of the central core and the solvent polarity. The molecules bear triphenylamine, oxadiazole and pyrene as electron donating, electron acceptor and π-conjugated edge substituents, respectively. Triphenylamine and pyrene substituents with fluorene-core as well as oxadiazole substituent with carbazole-core constitute the optimum selections for enhanced TPA properties. Studying the effect of the solvent polarity it is shown that maximum TPA cross-sections (as high as 1024 GM) are achieved in a solvent of intermediate polarity.

SERS spectra of methylene blue adsorbed on cap-shaped silver nanoparticles.Silver nanocaps were prepared by chemical synthesis combined with physical evaporation technique, and characterized using TEM, SEM and UV–vis-NIR spectroscopy. The surface-enhanced Raman scattering (SERS) activities of these nanoparticles were investigated using methylene blue (MB) as probe molecule. The enhancement factor was estimated to be as large as 4.2 × 107. The results demonstrate that these silver nanocaps are promising for SERS applications in detection and analysis of molecules.

Graphical depiction of n-tetradecane molecules on a graphite surface when the surface is fully covered.In this Letter, we investigate, using molecular dynamics simulations, the diffusion of n-octane and n-tetradecane on a graphite surface at 300 K under incomplete coverage condition. For both molecules, we observe that the lateral diffusion coefficient exhibits a Λ-shape anomaly with surface coverage i.e., the diffusion coefficient increases with the increase in surface coverage until a critical surface coverage, beyond which the diffusion coefficient decreases. Moreover, for low surface coverages, the longer n-tetradecane molecule moves faster compared to the shorter n-octane molecule and for high surface coverages, the n-octane molecule moves faster. We develop a new theory to understand the surface diffusion of n-alkanes and show that D ∼ r ee 2 N p τ R .

He intercalated C60 solid under high pressure by S. Kawasaki; T. Hara; A. Iwata (316-319).
This is the first study to precisely investigate the structural property of the He intercalated C60 under high pressure in a few tens GPa range.In situ synchrotron X-ray diffraction measurement of solid C60 under high pressure up to about 26 GPa was performed using He gas as pressure transmitting medium. This is the first study to precisely investigate the structural property of the He intercalated C60 under high pressure in a few tens GPa range. It was found that the He intercalated C60 solid is much less compressible than the pure C60 solid. The bulk modulus of the He intercalated C60 solid is determined to be B 0  = 35.1 (6.0) GPa. The effect of hydrostaticity on the deformations of unit cell and C60 molecule is also discussed.

Electron emission from carbon film on island-like tin oxide layer by Dan Zhu; Dejie Li; Jian Wang (320-323).
A new type of electron emitter composed of carbon film on island-like tin oxide layer is realized with 1% efficiency.Electron emission from carbon film on top of island-like tin oxide layer is proposed and demonstrated in this Letter. The tin oxide layer, consisting of regular islands in size of tens of nanometers, induces local heating to the carbon film and helps in forming the electron emission area. Electron emission with good stability and uniformity is reproducibly obtained with emission efficiency up to 1% under an anode voltage of 3 KV applied at 2 mm away.

The effect of the protein environment and the structural difference on the electronic structure of the special pair and the special pair cation radical in the photosynthetic reaction center were studied with density functional theory using polarizable continuum model and point charge model.We have studied the effect of structural differences and protein environment on electronic asymmetry of the special pair (SP) and the special pair cation radical in the bacterial photosynthetic reaction center with density functional theory. The electronic asymmetry has been found to derive from the difference in the orientation of methyl ester groups of SP halves. Due to the protein polarity enhancement with polarizable continuum model and point charge model, one electron oxidation is more significantly biased to the L-side bacteriochlorophyll a (SPL) in the both models.

Vibrational frequency analysis for the Watson–Crick guanine–cytosine (GC) base pair in the ground and lowest single ππ excited state was performed based on the reference geometry optimized at the HF/6-311G(d,p) and CIS/6-311G(d,p) levels, respectively. It was found that different NH and CH stretching vibrations can be used for the qualitative prediction of excited state geometrical non-planarity and the localization of electronic excitations in the base pair complexes.Vibrational frequency analysis for the Watson–Crick guanine–cytosine (GC) base pair in the ground and lowest single ππ excited state was performed based on the reference geometry optimized at the HF/6-311G(d,p) and CIS/6-311G(d,p) levels, respectively. It was found that different NH and CH stretching vibrations can be used for the qualitative prediction of excited state geometrical non-planarity and the localization of electronic excitations in the base pair complexes.

Competitive binding effects on surface-enhanced Raman scattering of peptide molecules by Leo Seballos; Nicole Richards; Daniel J. Stevens; Mira Patel; Laura Kapitzky; Scott Lokey; Glenn Millhauser; Jin Z. Zhang (335-339).
Various tyrosine (Y), proline (P) and tryptophan (W) containing peptides were studied to understand molecular binding on a SERS substrate.Surface enhanced Raman scattering (SERS) has been conducted on tryptophan (W), proline (P) and tyrosine (Y) containing peptides that include W-P-Y, Y-P-W, W-P-P-P-Y, Y-P-P-P-W, W-P-P-P-P-P-Y, and Y-P-P-P-P-P-W to gain insight into molecular binding behavior on a metal substrate to eventually apply in protein SERS detection. The peptides are shown to bind through the molecule’s carboxylic end, but the strong affinity of the tryptophan residue to the substrate surface, in conjunction with its large polarizability, dominates each molecule’s SERS signal with the strong presence of its ring modes in all samples. These results are important for understanding SERS of protein molecules.

A true chemical clock: Serially coupled chlorite–iodide oscillators by David A. Long; Leah Chodroff; Tim M. O’Neal; Sheryl Hemkin (340-344).
A theoretical chemical clock results from a model of coupled reactors that oscillate with frequencies of minutes, hours, and days.A set of serially coupled flow reactors are modeled which contain chlorite–iodide oscillators. By independently varying the reactor flow rates it is possible to produce oscillatory systems with differing periods where the ratio of the period of oscillation between reactors is always an integer value. This system was thoroughly examined and utilized to produce a ‘true’ chemical clock whose three reactors oscillate with a frequency of minutes, hours, and days.

The aurophilic attraction and the spectroscopic properties of [ Au 3 ( MeN=COMe ) 3 ] n ( n = 1 – 4 ) were studied. All complexes showed MMCT and MLCT transitions interrelated with the gold–gold intermolecular distanced.The aurophilic attraction and the spectroscopic properties of [ Au 3 ( MeN=COMe ) 3 ] n ( n = 1 – 4 ) were studied at the MP2 and density functional theory (B3LYP and PBE) levels. Theoretical calculations at the MP2 level are in agreement with experimental geometries and aurophilic attraction, and to a lower extent for PBE. The absorption spectra of these gold(I) complexes were calculated by the single-excitation time-dependent (TD) density functional method. All complexes showed MMCT and MLCT transitions interrelated with the gold–gold intermolecular distance. The values obtained at the PBE level are in agreement with the experimental range.

A direct investigation of this reaction is impossible because of chemical instability, but two-laser experiments do the trick.The title reaction turns the photoionization of the metal-to-ligand charge-transfer state MLCT of the ruthenium(II)-tris-bipyridyl ion into a catalytic cycle of photoinduced water splitting. To isolate that key step from the complex reaction scheme, the metastable oxidized form OX, [Ru(bpy)3]3+, is prepared by a first laser flash, and then photoreduced by a second. An analysis is presented that yields the efficiency η of the photoreduction from the intensity dependences of the concentrations of MLCT and OX. When water is the donor, η is only about 0.5; for alcohols (1-butanol, 2-propanol, tert-butanol) it is 1.

Peculiarities of light propagation through the media of molecules with long-lived photoexcited states by Marina V. Olenchuk; Yuri M. Barabash; Leonid N. Christophorov; Valeriy N. Kharkyanen (358-363).
Light intensity distribution in a two-side illuminated sample 10 mm length as compared with that given by Bouguer’s law.A theory of light propagation through the samples of molecules having anomalously long-lived photoexcited states is developed with an emphasis on the sample size. Application of the theory to experiments on a specific biomolecular system (redox reactions of the secondary acceptor of the bacterial photosynthetic reaction centre) leads to essential quantitative and qualitative re-evaluation of the results of conventional optico-spectroscopic determination of the reaction rates.

We investigate influence of delay feedback on pattern formation in reaction–diffusion system. Delay feedback unusually induces two instabilities.The influence of delay feedback (DF) on pattern formation in reaction–diffusion system is investigated in the parametric domain where the undelayed system exhibits uniform oscillations. Depending on the feedback parameters, both traveling patterns and standing patterns are observed. The linear stability analysis implies the traveling patterns arise from an oscillatory instability at a finite wavenumber (wave instability), whereas the standing patterns are formed due to another type of instability – the instability of homogeneous limit cycle with respect to spatial perturbations. It is demonstrated that, rather than stabilizing the system, the DF can unusually induce two kinds of instability.

It is shown that the ordinary form of the Ritz-optimized Hylleraas functional is a particular case of the general determinantal equation derived in the case of bivariational functionals.It is shown that the ordinary form of the Ritz-optimized second-order Hylleraas functional is a particular case of the general determinantal equation derived by Battezzati in his studies on bivariational functionals.

The design and experimental implementation of an effective z-rotation wPMLG sequence for 1H spectroscopy in solid-state NMR is demonstrated with a scale factor independent of radio-frequency imperfections.High-resolution 1H spectroscopy in solid-state NMR, rendered difficult due to the strong 1H–1H homonuclear dipolar coupling, has been made possible under magic-angle spinning with homonuclear dipolar decoupling schemes, such as windowed phase-modulated Lee–Goldburg. Here, we outline the theory and implementation of a modification of this scheme with which an effective z-rotation for the magnetisation is obtained over a wide range of spectral window. Experimental results are presented for samples, such as glycine, histidine, and tryosine.

Electrofugality index for benzhydryl derivatives by Paola R. Campodónico; Claudio Pérez; Margarita Aliaga; Marcela Gazitúa; Renato Contreras (375-378).
The regional electron-donating power at the nucleophilic end of a molecule assesses well its electrofugality pattern.We propose and test an empirical electrofugality index to rank the leaving group ability of a series of 21 benzhydryl derivatives. The empirical model defines the electrofugality as the negative of the global electrophilicity of the carbocation intermediate in the hydrolysis reaction. The results are in good agreement with the experimental electrofugality scale proposed for the title compounds by Mayr and coworkers [B. Denegri, A. Streiter, S. Júric, A.R. Ofial, O. Kronja, H. Mayr, Chem. Eur. J. 12 (2006) 1648].

Line tension effect on the water/air interfacial energy induced by the texture of PTFE substrates where air bubbles are anchored.We measured water/air interfacial energy as functions of the finest texture radius of annealed PTFE substrates where air bubbles are anchored. The calculated line tension from measured force vs distance curves for a 7 nm PTFE substrate texture radius is (28 ± 8) × 10−9  N. However, the most surprising aspect is that this effect is not restricted to the triple line vicinity, previously estimated to be ∼100 Å but spreads all over the water/air bubble interface. The proposed method is an alternative to the controversial contact angle measurement for estimating the line tension contribution.

Some properties of the largest eigenvalue Λ 1 of the distance matrix of a connected graph, such as the upper and lower bounds for Λ 1, are reported. The relationship between Λ 1 and the first Zagreb index and the Wiener index is given. Additionally, the Nordhaus–Gaddum-type result for Λ 1 is also presented.We report some properties of the largest eigenvalue Λ 1 of the distance matrix of a connected graph, in particular, the upper and lower bounds for Λ 1 involving the sum of the squares of the distances between all unordered pairs of vertices and the sum of the distances between a given vertex and all other vertices. We also give the relationship between Λ 1 and the first Zagreb index and the Wiener index. Additionally, we give the Nordhaus–Gaddum-type result for Λ 1.

Author Index (388-394).