Chemical Physics Letters (v.465, #1-3)
Editorial Board (IFC).
On the formation of higher carbon oxides in extreme environments by Ralf I. Kaiser; Alexander M. Mebel (1-9).
Due to the importance of higher carbon oxides of the general formula CO x (x > 2) in atmospheric chemistry, isotopic enrichment processes, low-temperature ices in the interstellar medium and in the outer solar system, as well as potential implications to high-energy materials, an overview on higher carbon oxides CO x (x = 3–6) is presented. This article reviews recent developments on these transient species. Future challenges and directions of this research field are highlighted.Due to the importance of higher carbon oxides of the general formula CO x (x > 2) in atmospheric chemistry, isotopic enrichment processes, low-temperature ices in the interstellar medium and in the outer solar system, as well as potential implications to high-energy materials, an overview on higher carbon oxides CO x (x = 3–6) is presented. This article reviews recent developments on these transient species. Future challenges and directions of this research field are highlighted.
Structural and energetic trends in Group-I and II hydrohelide cations by Alister J. Page; Ellak I. von Nagy-Felsobuki (10-14).
The structures and stabilities of Group-I and II hydrohelide cations were investigated using relativistically-corrected CCSD(T) and IC-MRCI.The ground states of HMHe+ (M = Li, Na, K) and HMHe2+ (M = Be, Mg, Ca) have been investigated using relativistically-corrected CCSD(T) and IC-MRCI. The HLiHe+, HBeHe2+, HNaHe+ and HMgHe2+ ions were found to be linear in the ground state. Conversely, HKHe+ and HCaHe2+ were quasi-linear, with 2 A ′ - 2 Σ + barrier heights of ca. 2 and 5 cm−1, respectively. Structural and energetic trends are consistent with H and He sharing covalent and electrostatic bonds with the metal ion, respectively. These trends are also seen to be strictly dependent on the polarisability of the central metal ion.
Experimental and theoretical study of the recombination reaction FSO2 + O2 → FS(O2)OO by M.E. Tucceri; M.P. Badenes; A.E. Croce; C.J. Cobos (15-19).
FSO3 absorbance recorded at 450 nm following the 193 nm photolysis of FS(O2)O(O2)SF. The addition of O2 modifies the decay due to the reaction FSO2 + O2 → FS(O2)OO.The kinetics of the recombination reaction FSO2 + O2 → FS(O2)OO has been studied at 298 K. FSO2 together with FSO3 radicals were generated by 193 nm laser flash photolysis of FS(O2)O(O2)SF. The measured rate coefficient at one atmosphere total pressure is k 1 = (4.6 ± 0.6) × 10−15 cm3 molecule−1 s−1. Molecular properties for the FS(O2)OO radical were calculated at the B3LYP/6-311+G(3df) and CCSD/6-311G(d) levels of theory. Consistent with the measured k 1 value, different density functional theory and Gaussian-3 calculations predict an electronic energy barrier for reaction close to 3 kcal mol−1.
Photoionization of atmospheric gases studied by time-resolved terahertz spectroscopy by Zoltan Mics; Petr Kužel; Pavel Jungwirth; Stephen E. Bradforth (20-24).
Optical pump–terahertz probe experiments in atmospheric gases were carried out to investigate the nascent electron-ion plasma.We investigate the laser induced ionization and plasma formation in pure oxygen and nitrogen by means of optical pump–terahertz probe spectroscopy. Focused amplified femtosecond pulses at 405 and 810 nm are used to ionize the gas molecules by nonlinear processes. The ionized gas is probed by picosecond terahertz pulses in the frequency range of 0.2–2 THz to obtain the free electron density (1013–1017 cm−3) and the electron scattering time (0.2 ps for N 2 and 0.4 ps for O 2 ). We demonstrate the importance of the centrifugal barrier for the photoionization process using circularly polarized light.
Short-range repulsion in the D 1 Σ 0 + -state potential of the ZnRg (Rg = Ne, Ar, Kr) complexes determined from a direct free ← bound excitation at the D 1 Σ 0 + ← X 1 Σ 0 + transition by M. Strojecki; M. Krośnicki; J. Koperski (25-30).
Analysis and simulation of the unstructured free ← bound profiles recorded for the first time in excitation spectra using the D 1 Σ 0 + ← X 1 Σ 0 + transition yield information on the short-range D 1 Σ 0 + -state potential of ZnNe, ZnAr and ZnKr complexes.Laser-induced fluorescence excitation spectra observed using the D 1 Σ 0 + ← X 1 Σ 0 + transition were used to determine the D 1 Σ 0 + -state potential in ZnNe, ZnAr and ZnKr. The complexes were produced in a free-jet expansion beam and excited with a dye-laser beam from the ground to the excited state. Analysis of the unstructured free ← bound profiles yielded information on the short-range repulsive part of the D 1 Σ 0 + -state potential. Ab initio calculations of the potential energy curves for the ground and excites states as well as for electronic transition dipole moments of the studied transition were performed taking scalar relativistic and spin–orbit effects into account.
Vibrational excitation functions for inelastic and superelastic electron scattering from the ground-electronic state in hot CO 2 by H. Kato; H. Kawahara; M. Hoshino; H. Tanaka; L. Campbell; M.J. Brunger (31-35).
Typical EELS spectrum of hot (700 K) CO2 at impact energy of 3.5 eV and scattering angle of 90°.We report inelastic and superelastic excitation function measurements for electron scattering from the ground vibrational quantum (0 0 0), the bending vibrational quantum (0 1 0) and the unresolved first bending overtone (0 2 0) and symmetric stretch (1 0 0) modes of the ground-electronic state in hot (700 K) carbon dioxide ( CO 2 ) molecules. The incident electron energy range of these measurements was 1–9 eV, with the relevant excitation functions being measured at the respective electron scattering angles of 30°, 60°, 90° and 120°. Where possible comparison is made to the often quite limited earlier data, with satisfactory agreement typically being found to within the cited experimental errors.
Elastic properties of aspirin in its crystalline and glassy phases studied by micro-Brillouin scattering by Jae-Hyeon Ko; Kwang-Sei Lee; Yuji Ike; Seiji Kojima (36-39).
Brillouin scattering spectrum of aspirin in its crystal and glassy phases.The acoustic waves propagating along the direction perpendicular to the (1 0 0) cleavage plane of aspirin crystal were investigated using micro-Brillouin spectroscopy from which C 11 , C 55 and C 66 were obtained. The temperature dependence of the longitudinal acoustic waves could be explained by normal anharmonic lattice models, while the transverse acoustic waves showed an abnormal increase in the hypersonic attenuation at low temperatures indicating their coupling to local remnant dynamics. The sound velocity as well as the attenuation of the longitudinal acoustic waves of glassy aspirin showed a substantial change at ∼235 K confirming a transition from glassy to supercooled liquid state in vitreous aspirin.
DNA compaction induced by neutral polymer is retarded more effectively by divalent anion than monovalent anion by Takuya Saito; Takafumi Iwaki; Kenichi Yoshikawa (40-44).
Effect of low-molecular weight anions (co-ions) on DNA compaction in a crowding medium.We studied the compaction of DNA in a crowding environment on poly(ethylene glycol) solution induced by the addition of salt, NaCl or Na 2 SO 4 , through single-DNA observation with particular focus on the effect of co-ions. We found that, at the same concentration of monovalent cation, divalent anions retard compaction more than monovalent anions, which means that greater ionic strength is not favorable for compaction. We discuss this effect in relation to the change in translational entropy of small ions accompanied by the breakdown of the physico-chemical framework of the screening ion atmosphere upon compaction.
Photoinduced ultrafast ring-opening reaction in trithianes in solution by Gotard Burdzinski; Bronislaw Marciniak (45-47).
Table of contents graphics: photochemistry of trithiane.The ring-opening reaction of trithianes possessing aromatic substituents has been studied using femtosecond broadband UV–Vis transient absorption spectroscopy. Photocleavage of the C―S bond occurs during the short-lived (1.5 ps) singlet excited state of trithiane. The products are formed with excess of vibrational energy and cooling of the hot molecules occurs with a 12.1 ps time constant in acetonitrile.
Theoretical investigation of equilibrium and transition state structures, binding energies and barrier heights of water-encapsulated open-cage fullerenone complexes by Tobias Pankewitz; Wim Klopper (48-52).
The barrier for H2O leaving the open cage is more than two times larger for fullerenone 1 than for 2.The encapsulation of a water molecule within two open-cage fullerenones with 18-membered-ring (1) or 19-membered-ring orifices (2) is studied by DFT with empirical dispersion terms. The equilibrium structure of each H2O@fullerenone and the transition-state structure for the water molecule leaving the cage are optimised and the counterpoise-corrected binding energy and barrier height are calculated. While the H2O binding energies in H2O@1 and H2O@2 are almost equal, the barrier for H2O leaving the cage is much higher for 1 (108 kJ mol−1) than for 2 (46 kJ mol−1). A water molecule can enter the cage-opened fullerenone 2 almost barrierless, whereas this barrier is 63 kJ mol−1 in 1.
Real-time observation of reversible spectral change of single pyridine2 molecules adsorbed on a glass surface by Kazuto Fukuhara; Atsuko Tsurumi; Masahiro Kotani (53-56).
Some single Pyridine2 molecules showed occasional spectral jump, which was found to be reversible.Spectrum change and intensity fluctuation of the fluorescence emitted by single pyridine2 (1-ethyl-4-(p-dimethylaminophenyl)-1,3-butadienyl)-pyridinium perchlorate; Py2) molecules adsorbed on a glass plate were measured at room temperature in real time by simple modification of a conventional optical microscope, i.e., by incorporating a transmission grating. The spectral shapes and peak wavelengths have wide distribution. The spectra could be classified into three distinct types. Most of the molecules exhibited one of the three types until they were finally photobleached, while some molecules showed occasional spectral jump to another type, which was found to be reversible. These results can be ascribed to the presence of several different conformers and photochemical isomerization.
Band unpinning and photovoltaic model for P3HT:PCBM organic bulk heterojunctions under illumination by Juan Bisquert; Germà Garcia-Belmonte; Antoni Munar; Michele Sessolo; Alejandra Soriano; Henk J. Bolink (57-62).
Linear plots of C −2 vs. voltage in P3HT-PCBM organic solar cells, shitf under illumination, indicating the charging of a surface state.Capacitance analysis of P3HT:PCBM bulk heterojunction solar cells, in dark and under illumination, shows a linear Mott–Schottky characteristic at moderate reverse bias, indicating p-doping of the organic blend. The flatband potential under illumination is displaced negatively about 0.6 V with respect to dark conditions. A basic photovoltaic model is developed to explain this, in terms of electron transfer via surface states at the metal/organic interface. Surface states with a slow exchange kinetics, become charged under illumination, unpinning the band and decreasing the depletion layer at the electron extraction contact. This becomes a major factor limiting the performance of bulk heterojunction solar cells.
First-principles calculations of the palladium(II) acetylacetonate crystal structure by Samir H. Mushrif; Alejandro D. Rey; Gilles H. Peslherbe (63-66).
The non-planar geometry of the palladium(II) acetylacetonate molecule observed experimentally in a crystal lattice was successfully reproduced with planewave-pseudopotential density-functional theory.The geometry of palladium(II) acetylacetonate in a monoclinic crystal lattice is calculated using the planewave-pseudopotential implementation of density-functional theory. Both the Troullier–Martin pseudopotential with the generalized gradient Perdew–Burke–Ernzerhof approximation and the Goedecker pseudopotential with the local density approximation are employed. The non-planar, step-like, structure of the molecule observed experimentally is successfully reproduced. A topological analysis of the electron localization function suggests a weak interaction between a Pd cation and the nearest carbon atom of the neighboring molecule of the closed-shell, non-electron-sharing type, presumably of electrostatic or dispersive nature, and possibly responsible for the bending of the palladium(II) acetylacetonate salt molecule in the crystal structure.
Local structure and time-resolved photoluminescence of emulsion prepared YAG nanoparticles by J.D. Furman; G. Gundiah; K. Page; N. Pizarro; A.K. Cheetham (67-72).
Increasing local disorder seen in the atomic thermal displacement parameter U(iso) corresponds to decreasing photoluminescent intensity in YAG:Ce nanoparticles.White LEDs rely on phosphors to convert blue or UV light into the broad spectrum emission needed for illumination. Nanoparticles of the Ce-doped yttrium aluminum garnet (YAG:Ce3+) phosphor were prepared by an emulsion route and calcined at various temperatures. The products were characterized by X-ray diffractometry, electron microscopy, and photoluminescence measurements, as well as time-resolved luminescent measurements at different temperatures (77–473 K). Quantitative Rietveld refinement with decreasing calcination temperatures and pair distribution function analyses, carried out with synchrotron X-ray data, revealed both luminescence quenching impurity phases and reduced long range correlation.
Phthalocyanines–MWCNT hybrid materials: Fabrication, aggregation and photoconductivity properties improvement by Zhenglong Yang; Hongting Pu; Junjie Yuan; Decheng Wan; Yongsheng Liu (73-77).
TEM images of CuPc(OC12H25)3(OC6H13)–MWCNT hybrid materials.The 2,9,16-trilauryloxy-23-hexyloxy substituted copper phthalocyanines multiwall carbon nanotubes (CuPc(OC12H25)3(OC6H13)–MWCNT) hybrid materials were facilely prepared by a chemical functionalization method. The aggregation structures of resulting hybrid materials have been characterized by TEM, SEM, FTIR, XRD and UV–vis measurements. The CuPc(OC12H25)3(OC6H13)–MWCNT hybrid materials exhibit good solution storage stability and a low aggregation tendency due to the chemical bonding between MWCNT and asymmetrically substituted phthalocyanines. The enhancement of the photoconductivity of phthalocyanines–MWCNT hybrid materials has been investigated in terms of interaction effects of phthalocyanines and MWCNT. It could supply a new way to fabricate a light energy conversion materials.
Size-dependent structural stability of ZnO nanowires and single-walled nanotubes by H. Li; Z.H. Jiang; Q. Jiang (78-81).
The size-dependent cohesive energy of one-dimensional nanowires and single-walled nanotubes of ZnO [E c(n)] is established, according to which their stability is considered.The size-dependent cohesive energy of one-dimensional nanowires and single-walled nanotubes of ZnO [E c(n)] is established based on considerations on surface bond deficit and curvature effects where n denotes atom number per periodic unit consisting of two ZnO layers. It is found that at n ∼ 48, both the structures have the same E c(n) value, which is a critical value for the size-dependent structural stability of the two structures. The model predictions are well in agreement with the first-principle calculation results.
Ti/C and Ti/h-BN nanocomposites: Comparison of hydrogen sorption/desorption properties by C. Borchers; O.S. Morozova; T.I. Khomenko; A.V. Leonov; E.Z. Kurmaev; A. Moewes; A. Pundt (82-85).
Differences in hydrogen uptake properties of Ti upon mechanical treatment with graphite or h-BN as additive are entropic in nature.The effect of graphite and BN on hydrogen absorption by Ti under milling in H2/He flow and on the thermal stability of Ti-hydride produced during milling is compared. BN is the more effective additive than graphite to improve hydrogen sorption capacity of Ti because of the stimulation of a higher hydrogen uptake. Both additives stimulate the formation of occupation sites characterized by a H2 desorption temperature that is up to 400 K lower than that of pure Ti. The reasons for the higher performance of hexagonal BN as compared to graphite are found to be entropic in nature.
Vibrations of the OHO hydrogen bond in t-butanol by Irena Majerz; Ireneusz Natkaniec (86-91).
Formation of the OHO hydrogen bond in t-butanol was reflected in shifting of the bands of the stretching and bending vibrations of OH group as well as arising of the bridge vibrations in the low frequency range of vibrational spectrum. INS spectroscopy appeared to be an important tool to investigate the low frequency range where out-of-plane OH deformation bands and hydrogen bridge stretching and bending bands are located.Experimental INS (Inelastic Neutron Scattering) spectrum of t-butanol was compared with theoretical spectra of t-butanol monomer and OHO hydrogen bonded dimer calculated at B3LYP/6-31++G∗∗ level. Formation of the OHO hydrogen bond was reflected in shifting of the bands of the stretching and bending vibrations of OH group as well as arising of the bridge vibrations in the low frequency range. INS spectroscopy appeared to be an important tool to investigate the low frequency range of the vibrational spectrum where out-of-plane OH deformation bands and hydrogen bridge stretching and bending bands are located.
Observation of surface plasmon-coupled emission using thin platinum films by Krishanu Ray; Mustafa H. Chowdhury; Joseph R. Lakowicz (92-95).
Surface plasmon-coupled emission was observed with thin platinum films at green and red wavelengths and was found to be mostly p-polarized.Surface plasmon-coupled emission (SPCE) is the directional radiation of light into a glass substrate due to excited fluorophores above a thin metal film. The sharp angular distribution of SPCE is a striking phenomenon and is in stark contrast with the isotropic fluorescence emission. In this Letter, we show that SPCE can occur with thin platinum films at green and red wavelengths and was found to be mostly p-polarized. This SPCE emission is the result of near-field interactions of the excited fluorophores with the thin platinum film, and is not simply a reflective or transmissive phenomenon. Our preliminary observation suggests that platinum nanostructures can be part of several novel bio-analysis surfaces.
Morphology and properties of a polyrotaxane based on γ-cyclodextrin and a polyfluorene copolymer by Aurica Farcas; Indrajit Ghosh; Nathalie Jarroux; Valeria Harabagiu; Philippe Guégan; Werner M. Nau (96-101).
In order to compare the electro-optical and morphological properties induced by the rotaxane architectures when γCD is used as host macrocycle, a rotaxane copolymer poly[2,7-(9,9-dioctylfluorene)-alt-2,7-fluorene/γCD)] (PF-γCD) and a non complexed reference copolymer (PF) were synthesized by Suzuki coupling.The effect of complexation of a poly[2,7-(9,9-dioctylfluorene-alt-2,7-fluorene)] copolymer into the inner cavity of γ-cyclodextrin on the morphology, the optical and the electrical properties was investigated. The fluorescence spectra of the rotaxane copolymer and of a reference, non complexed copolymer exhibit typical well resolved blue emission bands arising from the fluorene chromophore units. The complexation of the fluorene copolymer chain increases the fluorescence lifetime from 0.54 to 0.59 ns and decreases the activation energy of the electrical conduction from 2.41 to 1.49 eV. The rotaxane copolymer presents higher semiconducting properties as compared to the reference copolymer.
End states and singlet–triplet degeneracy in linear atomic chains by Antonio Monari; Valentina Vetere; Gian Luigi Bendazzoli; Stefano Evangelisti; Beate Paulus (102-105).
Linear Be chains are characterized by the presence of ‘edge states’ which results in a singlet–triplet quasi-degeneracy.The electronic structure of linear Beryllium chains has been theoretically studied by using ab initio methods. It turns out that, for internuclear distances close to the equilibrium structure, two partially filled edge orbitals (‘end states’) localize at the chain ends. This gives rise to two low-lying states, a singlet ground state, 1 Σ g , and a quasi-degenerate triplet, 3 Σ u . The energy splitting goes rapidly to zero as the number of atoms in the chain is increased. Preliminary investigations indicate that this could be a general behavior shared by the metals belonging to the Groups 2 and 12.
Towards size-converged properties of model ceria nanoparticles: Monitoring by adsorbed CO using DFT + U approach by Annapaola Migani; Christoph Loschen; Francesc Illas; Konstantin M. Neyman (106-109).
This work addresses the issue of smallest ceria nanoparticles, for which adsorption parameters become sufficiently independent of the particle size so that these particles can be used as representative models of notably larger particles commonly studied experimentally.Catalytic performance of ceria-supported metals can be dramatically improved when the support is in the form of nanoparticles rather than bulky samples. To rationalize this finding, ceria nanoparticle models are required that are tractable at a high computational level albeit adequately represent surface properties of larger moieties dealt with experimentally. This work addresses the issue of smallest ceria nanoparticles, for which adsorption parameters become sufficiently independent of the particle size. For that, adsorption of a CO probe molecule on a particular surface site of a series of model nanoparticles containing ∼50–230 atoms has been calculated using the DFT + U approach.
Synthesis and assembly of Bi2S3 nanoparticles at the water–toluene interface by Dongbo Fan; P. John Thomas; Paul O’Brien (110-114).
Bi2S3 nanoparticles, synthesized at the water–oil interface, self-assemble into nanorods that aggregate to globular forms.Nanoparticles of Bi2S3 synthesized at the interface of water and toluene undergo hierarchical assembly yielding nanorods that further aggregate to globules that form a deposit suspended at the interface. The obtained films have been characterized by X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy. The mechanism of growth is ascertained by studying experimental factors that influence this unusual assembly process.
Solid-state electronic conductivity of ruthenium nanoparticles passivated by metal–carbon covalent bonds by Debraj Ghosh; Shaowei Chen (115-119).
Ruthenium nanoparticles stabilized by Ru–C covalent bonds exhibited metal-like temperature dependence of the electronic conductivity, and an electronic coupling coefficient (β) of 0.48 Å−1.Stable ruthenium nanoparticles were prepared by passivation of the metal cores (diameter 2.7–3.2 nm by transmission electron microscopy) with ruthenium–carbon covalent bonds. Electrochemical study showed that the electronic conductivity of the particle films exhibited metal-like temperature dependence, and it decayed exponentially with the length of the alkyl spacer of the aliphatic protecting ligands, with an electronic coupling coefficient (β) of 0.48 Å−1. This was ascribed to the strong Ru–C bonding interaction and low interfacial contact resistance where the spilling of core electrons into the organic protecting shell led to enhanced interparticle charge transfer.
Chelating power of LR-74, a new AGE-inhibitor by J. Ortega-Castro; M. Adrover; J. Frau; J. Donoso; F. Muñoz (120-125).
Theoretical calculations of the complexes formed between Cu2+ ion and 2-(8-quinolinoxy)propionic acid (LR-74), a potent inhibitor of non-enzymatic glycation reactions.Theoretical calculations based on pseudo-potentials were used to determine the structures of the complexes formed between Cu2+ ion and 2-(8-quinolinoxy)propionic acid (LR-74), which is a potent inhibitor of non-enzymatic glycation reactions. The most stable among such complexes consist of one atom of copper and two molecules of inhibitor, [Cu(LR-74)2], and possess a distorted octahedral geometry. In the complex containing a single molecule of inhibitor, the square planar form, [Cu(LR-74)(H2O)]+, is slightly more stable than the octahedral form, [Cu(LR-74)(H2O)3]+, in solution. All octahedral complexes exhibit strong Jahn–Teller distortion that results in substantially increased axial distances.
How does urea really denature myoglobin? by L. Muthuselvi; Reinhard Miller; A. Dhathathreyan (126-130).
The experimental data for denaturation of myoglobin in aqueous solutions by urea for concentrations ranging from 0.1 M to 15 M using quartz crystal microbalance (QCM), circular dichroism (CD) and dilational rheology are examined with respect to a ‘structure-breaking effect’ of urea on the aqueous phase. Our study shows that any proposed denaturation mechanism of large biomolecules requires very high concentrations of urea and the association of urea with protein–water system is based on enhancement of hydrophobic interactions.This study reports on a model for denaturation of myoglobin by urea for concentrations ranging from 0.1 M to 15 M. The experimental data from quartz crystal microbalance (QCM), circular dichroism (CD) and dilational rheology are examined with respect to a ‘structure-breaking effect’ of urea on the aqueous phase. Even at urea concentrations >10 M, native conformation of the protein is retained through a restabilization of the hydrophobic association. Our study shows that any proposed denaturation mechanism of large biomolecules requires very high concentrations of urea and the association of urea with protein–water system is based on enhancement of hydrophobic interactions.
Concentration profile within diffusion layer under non-forced hydrodynamic conditions measured by Michelson interferometer by Hongjun You; Jixiang Fang; Feng Chen; Chao Zhu; Xiaoping Song; Bingjun Ding (131-135).
Concentration profile within diffusion field is measured and compared with theory result deduced from Amatore model.Michelson interferometer was developed to measure the concentration profile within diffusion layer in a galvanic displacement reaction system. A steady diffusion layer was achieved near the working electrode due to natural convection, viz., at long time and without any forced hydrodynamics. The concentration difference within diffusion layer is directly proportional to the distance of interference fringe deviated from linear one of bulk solution. Therefore, the concentration profile in diffusion layer can be measured from interference fringe. The validity of theory model deduced by Amatore and co-workers was further validated in our experiment.
Incremental expansions for SCF interaction energies: A comparison for hydrogen-bonded clusters by R.A. Mata; H. Stoll (136-141).
An analysis of embedding potentials for use within incremental expansions of SCF interaction energies.We present an analysis of several types of embedding potentials for use within incremental expansions of SCF interaction energies. The test set comprises hydrogen-bonded clusters (water, ammonia, methanol). It is shown that an expansion up to two-body terms is sufficient for high accuracy, in all cases, as long as the environment is described by accurate embedded-monomer Coulomb and exchange potentials. A two-body expansion with atom-centered point charges for embedding leads to larger errors, but the relative differences are kept within bounds; inclusion of three-body terms often overcompensates the deviations at the two-body level, due to basis set superposition effects.
Equiconducting molecular conductors by P.W. Fowler; B.T. Pickup; T.Z. Todorova (142-146).
Within the tight-binding approximation, non-isomorphic single-molecule conductors may be equiconducting i.e., have identical transmission functions.Non-isomorphic single-molecule conductors can have transmission functions that are identical at all electron energies, within the Hückel tight-binding approximation. These equiconducting cases follow from the graph-theoretical nature of the transmission function, and the existence of isospectral chemical graphs. Systematic constructions of equiconducting molecular graphs are presented, relying on the notions of isospectral pairs and isospectral vertices. These allow identification of non-isomorphic equiconducting connection patterns for a given molecule, and infinite families of equiconducting non-isomorphic molecules.
Direct measurement of diffusion in liquid phase by electron spin resonance by Aharon Blank; Yael Talmon; Michael Shklyar; Lazar Shtirberg; Wolfgang Harneit (147-152).
Graphical summary of the motion measurement capabilities for various methods (rough outline). Black line shows the diffusion length, 4 Dt , for D = 1 × 10−9 m2/s.Pulsed-gradient spin-echo (PGSE) NMR is a powerful technique that can directly measure the self-diffusion coefficient of molecules in a variety of environments. PGSE NMR can typically measure motions of at least ∼1015 molecules in the milliseconds-to-seconds time scale. Here we demonstrate for the first time that through the use of a unique miniature resonator and powerful and rapid gradient sources, electron spin resonance (ESR) can also be employed to measure diffusion in liquid state. The PGSE ESR method, which operates at the microseconds time scale with much higher molecular sensitivity, can complement and enhance the current capabilities of NMR.
X-ray absorption spectroscopy measured in resonant X-ray scattering mode: How unnatural is the resolution beyond the natural width? by Yasen Velkov; Yasumasa Hikosaka; Eiji Shigemasa; Sergey Gavrilyuk; Faris Gel’mukhanov (153-156).
X-ray spectroscopy of super-high resolution is a compromise with the uncertainty of predetermination of X-ray absorption resonance positions.The aim of this work is to give a clarifying view of the ‘super-high resolution’ scheme employing X-ray absorption spectroscopy in the resonant scattering mode. If the idea is not applied carefully, unrealistic results, as ‘perfect’ resolution, can be produced. The background of the problem is that the technique of extracting lifetime-broadening-free spectra assumes a known location of the resonance in the two-dimensional map of X-ray scattering spectra. The accuracy of the latter is, however, related to the lifetime broadening of the core-excited state. Thus, a compromise must be found between the uncertainty in the position of the X-ray absorption peak and the width of the desired absorption profile.
The Douglas–Kroll–Hess electron density at an atomic nucleus by Remigius Mastalerz; Roland Lindh; Markus Reiher (157-164).
High-order picture-change corrected Douglas–Kroll–Hess electron densities are analyzed at the atomic nuclei.The picture-change error on Douglas–Kroll–Hess (DKH) electron densities at atomic nuclei is analyzed in detail to high orders. Our results demonstrate that high-order DKH transformations of especially the property operator are needed to obtain converged results. However, if the convergence properties are discussed in terms of a relative error a fast convergence of the picture-change corrected DKH electron density at nuclei with the DKH order of orbitals and property operator is found. Furthermore, our results suggest that already the standard low-order DKH(2,2) model is likely to yield sufficiently accurate difference densities up to the third row of the periodic table.
Erratum to: ‘Molecular dynamics simulations of an apoliprotein A-I derived peptide in explicit water’ [Chem. Phys. Lett. 461 (2008) 294] by Athanassios Stavrakoudis (165).