Chemical Physics Letters (v.473, #1-3)
Editorial Board (IFC).
A synchrotron for neutral molecules by Cynthia E. Heiner; Hendrick L. Bethlem; Gerard Meijer (1-9).
Illustration of the split-hexapole molecular synchrotron, along with a measurement showing a packet of ND3 molecules completing 40 round trips in the synchrotron.Here we report on a synchrotron for neutral molecules that consists of two hexapole focusers bent into a torus. By switching the voltages applied to the two half-rings, polar molecules can be confined in tight packets for up to a second as they revolve around the ring. In this Letter, the operation and trapping parameters of the molecular synchrotron are discussed. We plan to use a molecular synchrotron in the future as an arena for low-energy collision experiments.
Inter-molecular vibrational frequencies of doubly hydrogen-bonded complexes involving 2-pyridone: Reliability of few selected theoretical level of calculations by Montu K. Hazra (10-16).
Inter-molecular vibrational frequencies of doubly hydrogen-bonded complexes involving 2-Pyridone: reliability of few selected theoretical level of calculations.The ground state fundamental inter-molecular vibrational frequencies of seven different doubly hydrogen-bonded mixed dimers involving 2-pyridone (2PY) have been predicted by different quantum chemistry calculations. Calculations have been performed by different DFT functionals with several basis sets and by the ab initio MP2/6-31G∗∗ level. The reliability of these calculations to predict the inter-molecular vibrations has been tested by comparing the experimentally measured and theoretically predicted values. Such vibrations have been measured by dispersed fluorescence (DF) spectroscopy. The comparison shows that the B3LYP/6-31+G∗∗, B3LYP/6-311++G∗∗ and MPWB1K/6-31+G∗∗ calculation predicted frequency values are in excellent agreement with the observed values and also to those predicted at MP2/6-31G∗∗ level of calculation.
Terpenes in the gas phase: The structural conformation of S-(–)-perillaldehyde investigated by microwave spectroscopy and quantum chemical calculations by Juan Ramón Avilés Moreno; Francisco Partal Ureña; Juan Jesús López González; Thérèse R. Huet (17-20).
Observed spectrum of pure rotational transitions of S-(–)-perillaldehyde in the 5 GHz region for the two most stable conformers. S-(–)-perillaldehyde (C10H14O) has been characterized in the gas phase using a Fourier transform microwave spectroscopy experiment in a supersonic molecular beam. Two conformers − with the isopropenyl group in the equatorial position − have been detected and described by a set of molecular parameters including the principal rotational constants and the quartic centrifugal distortion parameters. Quantum chemical calculations indicate that a third conformer might not be observed due to relaxation processes in the jet. The gas phase results are compared with the liquid phase IR–Raman–VCD spectra. Our study shows that gas phase spectroscopy is a powerful tool for characterizing monoterpenes.
The hyperfine structure in the rotational spectrum of water: Lamb-dip technique and quantum-chemical calculations by Gabriele Cazzoli; Cristina Puzzarini; Michael E. Harding; Jürgen Gauss (21-25).
The J = 1 1 , 0 ← 1 0 , 1 rotational transition of H 2 16 O . The simulations of the spectrum containing only hyperfine components (‘only real’) and of that containing both hyperfine components and crossing resonances (‘ghost + real’) are compared to the experimental spectrum.Seven ortho rotational transitions have been recorded for the main isotopic species of water in the millimeter- and submillimeter-wave region using the Lamb-dip technique in order to resolve the hyperfine structure due to the hydrogens and to provide accurate hyperfine constants. The experimental determination has been supplemented by high-level quantum-chemical calculations of the hyperfine parameters thereby focusing in particular on a systematic study of the basis-set convergence and on vibrational effects.
The weakly-bound nitrous oxide–acetylene complex: Fundamental and torsional combination bands of N2O–C2H2 and N2O–C2D2 in the N2O ν 1 region by M. Dehghany; Mahin Afshari; J. Norooz Oliaee; N. Moazzen-Ahmadi; A.R.W. McKellar (26-29).
Infrared spectra of the weakly-bound N2O–C2H2 and N2O–C2D2 complexes have been studied in a pulsed supersonic jet.Spectra of the weakly-bound N2O–C2H2 and N2O–C2D2 complexes in the region of the N2O ν 1 fundamental band (∼2224 cm−1) are observed in a pulsed supersonic slit jet expansion probed with a tunable diode laser. Two bands are analyzed for each complex: the fundamental (N–N stretch), and a combination involving the intermolecular torsional (out-of-plane bend) vibration. The resulting torsional frequencies are 44.37 and 40.01 cm−1 for the C2H2 and C2D2 complexes, respectively. This represents the first observation of the N2O–C2D2 isotopomer, and the first direct determination of an intermolecular frequency for nitrous oxide–acetylene.
Kinetic study of the reactions of chlorine atoms with ethyl vinyl ether and propyl vinyl ether by Lei Wang; Maofa Ge; Weigang Wang (30-33).
By using a discharge flow-tube system, we determine the rate constants of reactions of Cl atoms with EVE (C2H5OC2H3) and PVE (C3H7OC2H3) under different conditions (253–298 K, 0.5–1.8 Torr). The results demonstrate that reactions of EVE and PVE with Cl atoms may play a significant role for the degradation of EVE and PVE.Kinetic study of the reactions of Cl atoms with EVE and PVE was performed using the absolute rate method over the temperature range 253–298 K at 1 Torr. The obtained Arrhenius expressions were k EVE = (8.0 ± 1.4) × 10−10 exp[(−349 ± 21)/T] cm3 molecule−1 s−1 and k PVE = (1.9 ± 0.3) × 10−9 exp[(−450 ± 18)/T] cm3 molecule−1 s−1. H-atom abstraction is likely to be the main reaction pathway as HCl was detected. The atmospheric lifetimes of EVE and PVE were evaluated, which demonstrates Cl atoms may play an important role for the sink of EVE and PVE.
Dissociative charge exchange of H 3 + and D 3 + with cesium: Dissociation dynamics and two- and three-body branching fractions by Jennifer E. Mann; Christopher M. Laperle; John D. Savee; Robert E. Continetti (34-38).
The kinetic energy release distributions for H3 and D3 were measured using charge exchange of H 3 + and D 3 + with Cs.The two-and three-body center-of-mass kinetic energy release distributions for H3 and D3 along with their branching fractions were measured using charge exchange of H 3 + and D 3 + with Cs. Vibrational and rotational excitation in the diatomic product and radiative decay to the repulsive ground state from a manifold of Rydberg states are observed in both systems. The two-body dissociation pathway is found to be dominant, however, for higher-lying Rydberg states, the three-body pathway becomes increasingly important.
Ab initio potential energy surfaces for the 1 A′ and 3 A′ states of the MgH(X2Σ+) + H(2S) system by D. Ben Abdallah; F. Najar; N. Jaidane; Z. Ben Lakhdar; N. Feautrier; A. Spielfiedel; F. Lique (39-42).
Contour plots of the MRCI + Q PES for the 1 A′ state correlating to the MgH(X2Σ+) + H(2S) asymptote. The MgH bond length is held fixed to 3.27 bohr.The two potential energy surfaces (PESs) associated to the 1 A′ and 3 A′ states correlating to the interacting MgH(X2Σ+) + H(2S) system were determined from ab initio calculations. They were obtained using the aug-cc-pVQZ basis set for the H atom and the cc-pV5Z basis set for the Mg atom and multireference internally contracted configuration-interaction (MRCI) method including Davidson correction. The MgH distance was kept fixed at its experimental equilibrium distance in the X2Σ ground state. The ab initio calculated interaction energies of the two PESs were fitted analytically on the basis of Legendre polynomials for future collisional rotational excitation study. The 1 A′ and 3 A′ adiabats both present very deep well corresponding to the MgH2 complex.
Infrared multiphoton dissociation spectrum of isolated protonated 1-azapyrene by Martin Vala; Jan Szczepanski; Robert Dunbar; Jos Oomens; Jeffrey D. Steill (43-48).
The infrared multiphoton dissociation spectrum of gaseous protonated 1-azapyrene has been determined and compared to density functional theory calculations.The infrared spectrum of protonated 1-azapyrene has been obtained by infrared multiphoton dissociation (IRMPD) spectroscopy using a Fourier-transform ion cyclotron resonance mass spectrometer coupled to an infrared tunable free electron laser. Found when electrospraying a pyrene/methanol/acetic acid solution, the carrier of the dominant m/z 204 peak was determined by comparison of the IRMPD spectrum with density functional theory calculations (B3LYP/6-31G(d,p)). The greater proton affinity and solubility of 1-azapyrene explains the competitive protonation of azapyrene over pyrene despite its apparent smaller abundance in the electrospray solution. The possible contribution of 1-azapyrene to the interstellar infrared emission bands is briefly discussed.
Theoretical approach to the conformational analysis of heteroaromatic dimers: 2-(2-Thienyl)pyrrole, 2-(2-thienyl)furan, and 2-(2-furyl)pyrrole by J.C. Sancho-García; A. Karpfen (49-56).
The torsions between different heteroaromatic units (thiophene, pyrrole, and furan) have been studied in great detail. The outcome of the benchmark calculations aims at further guiding the modeling of polymer folding at conformational defects.The torsional potentials for inter-ring rotation in 2-(2-thienyl)pyrrole, 2-(2-thienyl)furan, and 2-(2-furyl)pyrrole are systematically studied by highly reliable and accurately convergent ab initio methods. The outcome of the state-of-the-art calculations is used in the investigations on structure and conformational preferences of these systems and aims at further guiding the modeling of polymer folding at conformational defects. A comparison is then made with those results provided by DFT approaches in order to assess the performance of the latter methods along the whole rotational path. Finally, we have assessed other cost effective yet more accurate DFT-based methods by fine-tuning the energy components entering into the model.
Rate constants for the gas phase reaction of ozone with n-butyl acrylate and ethyl methacrylate by Yanbo Gai; Maofa Ge; Weigang Wang (57-60).
Rate constants for the reaction of ozone with n-butyl acrylate (BUAC) and ethyl methacrylate (ETMEAC) at 293 K are determined for the first time using absolute rate method with cyclohexane as OH scavenger.Rate constants for the reaction of ozone with n-butyl acrylate (BUAC) and ethyl methacrylate (ETMEAC) have been investigated for the first time. At 293 ± 1 K and atmospheric pressure, the measured values were (2.40 ± 0.29) × 10−18 cm3 molecule−1 s−1 for BUAC and (7.68 ± 0.88) × 10−18 cm3 molecule−1 s−1 for ETMEAC. The atmospheric lifetimes have also been estimated, which indicate that only in the polluted areas could reaction with ozone be one of the important sinks for these unsaturated esters.
First principles studies of ZrNi and ZrNiH3 by S.F. Matar (61-65).
Changes in electronic structure due to hydrogen uptake within ZrNi alloy system leading to the experimental hydride composition ZrNiH 3 , are examined ab initio using both pseudo-potential and all electron calculations. In order to establish trends in stability hypothetic ZrNiH and ZrNiH 2 are also examined and proposed to act as transition phases in a stepwise hydrogen desorption process. Analyses of the site projected density of states and of the chemical bonding point to meaningful changes of the electronic structure whereby hydrogen brings new states within the valence band and is found to preferably bind with Ni rather than with Zr.
Molecular dynamics simulation of liquid–vapor phase equilibria in polar fluids by Hossein Eslami; Ali Dargahi; Hassan Behnejad (66-71).
A molecular dynamics simulation scheme for calculation of vapor–liquid equilibria of polar compounds.A new molecular dynamics simulation technique in the grand canonical ensemble [H. Eslami, F. Müller-Plathe, J. Comput. Chem. 28 (2007) 1763], has been employed to calculate the chemical potentials in the coexisting liquid and vapor phases of pure water, methanol, and acetonitrile. Calculating the chemical potentials in the liquid phase, a new method [J. Vrabec, H. Hasse, Mol. Phys. 100 (2002) 3375], has been employed to calculate the phase coexistence point. In this method just two independent simulations in the grand canonical ensemble are needed to be performed and the molecules are inserted into or deleted from the system in a dynamical way.
X-ray diffraction studies and equation of state of methane at 202 GPa by Liling Sun; Wei Yi; Lin Wang; Jinfu Shu; Stas Sinogeikin; Yue Meng; Guoyin Shen; Ligang Bai; Yanchuan Li; Jing Liu; Ho-kwang Mao; Wendy L. Mao (72-74).
X-ray images of the solid CH4 at three pressures, showing the high pressure phase with cubic structure persisting up to 202 GPa. At high pressure the XRD from the sample became increasingly weaker. To improve the quality of XRD pattern, we reduced the X-ray focus spot size and clean-up slits at 171 GPa, and increased the exposure time for each measurement.Solid methane (CH4) was compressed up to 202 GPa at 300 K in a diamond-anvil cell. The crystal structure and equation of state over this entire range were determined from angle dispersive X-ray diffraction results. CH4 undergoes phase transitions from rhombohedral to a simple cubic phase at 19 GPa and from simple cubic to a higher pressure cubic phase at approximately 94 GPa. This higher pressure cubic phase was stable to the maximum pressure investigated. Combined with previous optical measurements, it was found that at room temperature compressed CH4 remains an insulator with cubic structure to 202 GPa.
The role of H-bonded chelate rings in the organization of liquid crystalline 2-hydroxyazobenzenes by Paulina Majewska; Maria Rospenk; Bogusława Czarnik-Matusewicz; Lucjan Sobczyk (75-80).
This work reports the role of H-bonded chelate rings in organization of 4-chloro-2′-hydroxy-4′-hexyloxyazobenzene, which shows liquid crystalline properties.Polarized infrared spectra of 4-chloro-2′-hydroxy-4′-hexyloxyazobenzene were studied from 25 to 120 °C encompassing transitions from the crystalline to the isotropic phase. The behavior of the ν(OH), δ(OH), and γ(OH) bands is analyzed. Based on the DFT calculations and on linear dichroism spectroscopy, it was concluded that the core-to-core interaction between hydrogen-bonded chelate rings is responsible for changes in intensity and shape of the bands. A pseudo-band at ca. 620 cm−1 is discussed based on Fermi resonance between the ν(OH) and γ(OH) modes. A general analysis is presented with respect to the directions of the transition moments of the particular modes.
The inelastic neutron scattering spectrum of nicotinic acid and its assignment by solid-state density functional theory by Matthew R. Hudson; Damian G. Allis; Bruce S. Hudson (81-87).
The 25 K inelastic neutron scattering spectrum of nicotinic acid has been measured and assigned and tautomerization investigated by solid-state density functional theory.The 25 K inelastic neutron scattering (INS) spectrum of nicotinic acid has been measured and assigned by solid-state density functional theory (DFT). Vibrational mode energies involving the carboxylic acid proton are found to be significantly altered due to intermolecular hydrogen-bonding. There is good overall agreement between experiment and simulation in all regions of the spectrum, with identified deviations considered in detail by spectral region: phonon (25–300 cm−1), molecular (300–1600 cm−1), and high-frequency (>2000 cm−1). The relative energies, geometries, and vibrational spectra associated with hypothesized tautomerization in the solid-state have also been investigated.
Anisotropic relaxation of Mn2+ and Ni2+ impurities in K2MgF4 by J.M. García-Lastra; M.T. Barriuso; J.A. Aramburu; M. Moreno (88-91).
Anisotropic local relaxation around Mn2+ and Ni2+ impurities in layered perovskites (K2MgF4 and K2ZnF4).The local relaxation around Mn2+ and Ni2+ impurities in K2MgF4 and also in K2ZnF4:Mn2+ has been explored by means of cluster calculations using Density Functional Theory. It is found that the difference between equatorial and axial Mg2+–F− distances in the K2MgF4 (K2ZnF4) when Mg2+ (Zn2+) is replaced by Mn2+ increases from 1.5 (−0.2) pm to 5 (3.5) pm. This surprising behaviour, consistent with the available EPR experiments, is shown to arise from the elastic anisotropy of the host lattice. From the present analysis it emerges that results which are valid for a transition-metal complex in a cubic lattice cannot in general be transferred to host lattices of lower symmetry. The results of this work confirm that the local distortion around a d9 ion in a layered compound cannot necessarily be associated with the Jahn–Teller effect.
Electronic structure and interactions of LiF doped tris (8-hydroxyquinoline) aluminum (Alq) by Huanjun Ding; Kiwan Park; Yongli Gao; Do Young Kim; Franky So (92-95).
The doping mechanism of co-evaporated LiF in Alq thin film is investigated with XPS and UPS.The electronic structure of co-evaporated LiF and tris (8-hydroxyquinoline) aluminum (Alq) films with different weight ratios have been investigated with ultraviolet and X-ray photoemission spectroscopy (UPS and XPS). The results indicate that pristine LiF has only a small n-doping effect. However, Alq films doped with freshly crushed LiF powder source show a much larger shift in the frontier orbital, suggesting that the doping is most probably induced by defects, as such effect disappears after several evaporations. The interactions of the LiF doped Alq with metal overlayers have also been investigated. Al causes significant n-doping of Alq, while Au does not, due to its inertness and p-doping nature.
Investigation of the light emission efficiency of single-wall carbon nanotubes wrapped with different surfactants by C. Fantini; J. Cassimiro; V.S.T. Peressinotto; F. Plentz; A.G. Souza Filho; C.A. Furtado; A.P. Santos (96-101).
Dependence of the absorption and emission of light on the concentration of nanotubes in aqueous dispersions.Single-wall carbon nanotubes dispersed in aqueous solutions of different surfactants are investigated by optical absorption and photoluminescence spectroscopies. The role played by the type of surfactant, surfactant concentration, and nanotube concentration on the efficiency of absorption and emission of light by the individualized nanotubes of different chiralities is discussed. By comparing the intensities of absorption and emission is possible to obtain the best nanotube and surfactant concentrations that optimize the light emission efficiency. Changes in the absorption and emission energies are observed and interpreted in terms of the variation of the environments screening on the exciton binding energies.
Simple solvothermal route to synthesize S-doped ZnO nanonails and ZnS/ZnO core/shell nanorods by Soumitra Kar; Paritosh Dutta; Tanusri Pal; Surajit Ghosh (102-107).
S-doped ZnO exhibiting intense green light emission property at room temperature has been synthesized by a simple solvothermal route. By tailoring the sulfur source concentration ZnS/ZnO core/shell nanorods could be synthesized by the same technique.A simple solvothermal route was successfully utilized to fabricate S-doped ZnO nanonails with a hexagonal cap followed by a comparatively thin long needle shaped stem portion. Diameters of the hexagonal caps varied within 10–25 nm and lengths of the stem portions varied within 50–80 nm. These nanonails were found to exhibit intense green light emission property at room temperature. Similar synthesis protocol was employed to fabricate ZnS/ZnO core/shell nanorods by suitably tailoring the concentration of the sulfur source in the synthesis environment.
Structural, electronic and elastic properties of ultra-light diamond-like crystalline allotropes of carbon-functionalized fullerenes C28 by Andrey N. Enyashin; Alexander L. Ivanovskii (108-110).
Due to the linking using acetylide groups between C28 fullerenes, a couple of fullerite structures may be obtained with composition C28C4, which will be the lightest among all known fullerites both with weak van-der-Waals’ and with strong covalent intercage binding. Chemical route for the chemical synthesis of these structures can be more successful, than previous experimental tests to prepare C28 fullerites using deposition of C28 molecules from gas-phase.The atomic models of [C28 + C4] fullerites based on C28 fullerenes bound by acetylide C2 bridges are offered. Their structural, elastic and electronic properties are predicted by means of the DFTB method and are discussed in comparison with topologically identical C28 allotropes. The calculations show that, due to unique structure of [C28 + C4] crystals, they would be the lightest among all known fullerites, while their bulk moduli will be essentially higher, than those for more dense C28 fullerites. We propose a possible route for the chemical synthesis of these structures composed of sp-, sp 2- and sp 3-hybridized atoms, which could be more successful, than previous experimental tests on adsorption of C28 from gas-phase.
Oxidation and magnetic properties of lead nanoparticles in different matrices by A. Sarkar; R. Chadha; T. Mukherjee; S. Kapoor (111-115).
Magnetization vs field at different temperatures for Pb nanoparticles.A systematic study was conducted for in situ synthesis of fine Pb nanoparticles in aqueous gelatin solution and in pre-organized gel of polyacrylamide. The Pb nanoparticles stabilized by gelatin or trapped in polyacrylamide matrix transfer electron to O2 and methyl viologen (paraquat; 1,1′-dimethyl-4,4′-dipyridinium dichloride; MV2+(Cl−)2). Lead nanoparticles were probed for their magnetic characteristics by superconducting quantum interference device (SQUID) magnetometer and display superconductivity with a critical temperature Tc of about 7.1 K. The magnetization measurements reveal the superconducting behaviour of Pb nanoparticles prepared in aqueous gelatin stabilized sol and corroborates the results obtained from electron transfer reactions.
Imaging 3-aminopropyltriethoxysilane self-assembled monolayers on nanostructured titania and tin (IV) oxide nanowires using colloidal silver nanoparticles by Andrew R. Morrill; Duc T. Duong; Seung Joon Lee; Martin Moskovits (116-119).
Binding silver colloidal nanoparticles onto 3-aminopropyltriethoxysilane-functionalized nanostructured TiO2 and SnO2 nanowires allows for surface characterization via scanning electron microscopy.Self-assembled monolayers (SAM) of 3-aminopropyltriethoxysilane (APTES) were grown on nanostructured titania (NST) and tin oxide nanowires (SnO2 NW) and the functionalized metal oxide surfaces were decorated with borohydride-reduced silver nanoparticles (AgNPs) and imaged. Comparative studies with the mono- and di-ethoxysilanes were also carried out. The nanoparticle-modified silane films are found to be greatly stabilized against oxidation. Because colloidal AgNP bind preferentially to the amino functionality of the silane molecules, they serve as an assay for the surface’s utility towards species that bind to that group. The particle density also reflects the relative number of natively bound APTES in the SAM.
Directional surface plasmon coupled chemiluminescence from nickel thin films: Fixed angle observation by Micah Weisenberg; Kadir Aslan; Elinor Hortle; Chris D. Geddes (120-125).
Surface plasmon coupled chemiluminescence from nickel thin films is highly directional and can be observed at a fixed angle.Directional surface plasmon coupled chemiluminescence (SPCC) from nickel thin films is demonstrated. Free-space and angular-dependent SPCC emission from blue, green and turquoise chemiluminescent solutions placed onto nickel thin films attached to a hemispherical prism were measured. SPCC emission was found to be highly directional and preferentially p-polarized, in contrast to the unpolarized and isotropic chemiluminescence emission. The largest SPCC emission for all chemiluminescence solutions was observed at a fixed observation angle of 60°, which was also predicted by theoretical Fresnel calculations. It was found that nickel thin films did not have a catalytic effect on chemiluminescence emission.
Efficient electrochemical reaction in hexagonal WO3 forests with a hierarchical nanostructure by Masachika Shibuya; Masahiro Miyauchi (126-130).
Reversible color change in WO3 nanotree electrode.Nanotree-like hexagonal tungsten oxide (WO3) arrays were grown on metal tungsten substrates by a facile hydrothermal method. The WO3 nanotrees, composed of ‘trunks’ and ‘branches’, were single crystals oriented in the 〈0 0 1〉 direction. Nanotree thin films exhibited efficient electrochromism due to their large tunnels in the crystal and nano-channels between the nanotrees. Moreover, their coloration efficiency and reversibility were superior to polycrystalline WO3 films.
Adsorption kinetics of methanol in carbon nanotubes revisited – solvent effects and pitfalls in ultra-high vacuum surface science experiments by M. Komarneni; A. Sand; J. Goering; U. Burghaus (131-134).
Experimentally determined binding energies for methanol adsorption on external sites increase with increasing CNT diameter. However, kinetics results can be obscured by rather subtle solvent effects which are probe molecule specific.Thermal desorption spectroscopy (TDS) allows for distinguishing among internal, external, and groove adsorption sites on carbon nanotubes (CNTs). Thus, TDS can be applied to study the effect of CNTs’ crystal structure on adsorption kinetics. On clean CNTs, the binding energy for methanol increases with increasing CNT diameter, consistent with theoretical predictions. However, kinetics results can be obscured by rather subtle solvent (impurity) effects which are probe molecule specific.
EPR experiments of Ag species supported on NaA by Amgalanbaatar Baldansuren; Emil Roduner (135-137).
Neutral silver atoms and triatomic silver clusters were observed by EPR following chemical reduction of AgNO3 exchanged into NaA zeolite.Ag/NaA was prepared by aqueous ion-exchange of Ag + against Na + and investigated using X-band EPR spectroscopy. After hydrogen reduction, the EPR signal at a loading of 6% (wt.) exhibiting axial g- and hyperfine tensors ( g ⊥ = 1.998 and g ‖ = 2.214 , coaxial with | A ⊥ | = 23 G and | A ‖ | = 173 G) was assigned to Ag atoms. The second species is observed at 9% (wt.) Ag and is a neutral triatomic Ag cluster of near-isotropic symmetry with g iso = 2.044 and | A iso | = 97.3 G .
Defects generation in single-walled carbon nanotubes induced by soft X-ray illumination by Yutaka Mera; Yoshihisa Harada; Satoshi Arima; Kenji Hata; Shik Shin; Koji Maeda (138-141).
Defects generation in single-walled carbon nanotubes induced by soft X-rays from a synchrotron radiation source was investigated.Defects generation in single-walled carbon nanotubes induced by soft X-rays from a synchrotron radiation source was investigated by in-situ C 1s soft X-ray absorption and recombination emission as well as ex-situ micro Raman scattering spectra. The spectral dependence of the defect generation efficiency shows that the illumination effect is resonantly enhanced in between the π∗ and σ∗ carbon 1s core absorption. A spectator Auger decay process is proposed as the most plausible mechanism for the defects generation.
State of water in hybrid sulfonated poly(ether ether ketone) – silica membranes by 1H solid-state NMR by Maria Baias; Dan E. Demco; Bernhard Blümich; Martin Möller (142-145).
The state of water in sulfonated poly(ether ether ketone) – silica membranes was investigated by 1H ODESSA and magnetization relaxation NMR.The state of water in fully hydrated sulfonated poly(ether ether ketone) – silica hybrid proton exchange membranes were characterized in terms of the exchange rate between bound and free water, the water dynamics in each phase, and the relative water populations by 1H ODESSA and transverse magnetization relaxation NMR. The exchange rate, the amount of bound water, and the reorientation of free water molecules increase in the presence of silica particles. The dynamics of bound water was described by the Lévy statistics with a Cauchy propagator. The proton exchange membranes performances could be improved by addition of small concentrations of silica in the range of 5–10 wt.%.
Guest species trapped inside carbon nanotubes by C.N. Ramachandran; Dario De Fazio; N. Sathyamurthy; V. Aquilanti (146-150).
Taking the torsional motion of H2O2 inside a carbon nanotube as an example, the interaction between the encapsulated guest species and the cage is studied using density functional theoretical method with B3LYP functional and 6-31G∗∗ basis set. Depending upon its orientation inside the nanotube, H2O2 binds differently with the cage so that its torsional motion is inhibited. The binding due to the weak O–H⋯π interaction is discussed. The polarization of the nanotube because of the guest species suggests that the molecular motion through the nanotube may be influenced by polar solvents and external electric field.Taking the torsional motion of H2O2 inside a carbon nanotube as an example, the interaction between the encapsulated guest species and the carbon nanotube has been studied using the density functional theoretical method with the B3LYP functional and the 6-31G∗∗ basis set. Depending upon its orientation inside the nanotube, H2O2 binds differently with the nanotube thereby inhibiting the torsional motion in the encapsulated state. The binding of the guest species with the nanotube due to the weak O–H⋯π interaction is discussed. The polarization of the nanotube because of the guest species suggests that the molecular motion through the nanotube may be influenced by polar solvents and external electric fields.
Generation of green, red and white light from rare-earth doped Ga2O3 nanoparticles by Godhuli Sinha; Amitava Patra (151-154).
We demonstrated white light emission from rare-earth doped Ga2O3 nanoparticle by energy transfer from Ga2O3 nanoparticle to rare-earth ions.We report the solvothermal synthesis of pure and rare-earth ions doped Ga2O3 nanoparticles for blue (Ga2O3), green (Tb3+) and red (Eu3+) emission. Bright white emission can be produced by tuning dopant ions. The CIE co-ordinate values of the white light are 0.32, 0.36, which are well within the white region of the chromaticity diagram. Steady state and time-resolved spectroscopic studies were performed to understand the mechanism. Analysis suggests that semiconducting Ga2O3 nanoparticles sensitize the rare-earth activator, which leads to an energy transfer system that produces a bright white light.
Cisplatin and its analogues induce a significant change in the higher-order structure of long duplex DNA by Yousuke Katsuda; Yuko Yoshikawa; Takaji Sato; Yoshihiro Saito; Masahiko Chikuma; Mari Suzuki; Kenichi Yoshikawa (155-159).
Conformational change of single DNA molecule induced by cisplatin.It has recently become clear that a long DNA with a size of more than several tens of kilo base-pairs (kbp) exhibits a large on/off change in conformation between elongated coil and folded compact states. To explore the possible effect of anticancer drugs on the conformation of large DNA, we observed single DNA molecules with regard to changes in their higher-order structure upon the addition of cisplatin and its derivatives, diamminedinitratoplatinum(II) and tetrammineplatinum(II). We found that these cisplatin analogues significantly affected the conformation of individual DNA molecules by inducing a folding transition.
Solvent effect on EPR, molecular and electronic properties of semiquinone radical derived from 3,4-dihydroxybenzoic acid as model for humic acid transient radicals: High-field EPR and DFT studies by Maciej Witwicki; Julia Jezierska; Andrzej Ozarowski (160-166).
Inclusion of water molecules in the hydration sphere of the radical is mandatory for correct prediction of its properties.The g-tensor components and isotropic hyperfine constants of solvent-affected radical anion from 3,4-dihydroxybenzoic acid were computed at UBP86/EPR-II level and correlated with the molecular and electronic structures. The role of solvent was considered in two ways: by using a conductor-like screening model (COSMO) and by adding water molecules, hydrogen bonded to the radical. To reach the best efficiency of the calculations, the theoretical EPR parameters were compared with experimental derived from high-field (406.4 GHz) and X-band spectra. Inclusion of water molecules in the first hydration sphere of the radical appears to be mandatory for correct prediction of its properties.
Transient spectroscopy of UV excited flavone: Triplet–triplet absorption and comparison with theory by Gernot Engler; Michael Nispel; Christel Marian; Karl Kleinermanns (167-170).
Density Functional/Multi Reference Configuration Interaction (DFT/MRCI) calculations permit assignment of the most intense T1–Tn transitions of flavone in cyclohexane.We reinvestigated the stationary singlet absorption spectrum of flavone and its transient triplet spectrum at excitation wavelengths of 266 and 355 nm in cyclohexane as solvent. The S0–Sn spectra obtained by Density Functional/Multi Reference Configuration Interaction (DFT/MRCI) calculations agree well with experiment. The calculated intense T1–Tn transitions qualitatively reproduce the experimental band maxima observed at ∼330, 365 and 600 nm in cyclohexane.
Ultrafast redistribution of vibrational energy after excitation of NH stretching modes in DNA oligomers by V. Kozich; Ł. Szyc; E.T.J. Nibbering; W. Werncke; T. Elsaesser (171-175).
The decay of the different NH stretching vibrations of DNA oligomers populates distinct accepting modes in the NH bending range.Vibrational relaxation after spectrally selective excitation within the NH stretching band of adenine–thymine base pairs in DNA oligomers was studied by subpicosecond infrared-pump/anti-Stokes Raman-probe spectroscopy. The decay of the different NH stretching vibrations populates distinct accepting modes in the NH bending range with a rise time of 0.6 ps that is close to the NH stretching decay times. The population of thymine fingerprint modes after excitation of the adenine antisymmetric NH2 stretching mode points to an ultrafast excitation transfer to the thymine NH stretching vibration before relaxation. The nonequilibrium fingerprint populations decay on a time scale of several picoseconds.
Hydrolysis of As(III): A femtosecond process by Anirban Bhattacharjee; Thomas S. Hofer; Andreas B. Pribil; Bernhard R. Randolf; Bernd M. Rode (176-178).
Realtime description of hydrolysis process of As(III) cation obtained employing ab initio quantum chemical treatment.A Quantum Mechanical Charge Field Molecular Dynamics (QMCF-MD) study of As(III) in aqueous medium was carried out, in order to gain insight into its solvation behavior, both in structural and dynamic aspects. Immediately after the formation of the hydrated As 3 + ion, a two step hydrolysis was observed resulting in the As(OH) 2 + species which seems to be the stable species of As(III) in water.
A systematic study of the influence of the slab thickness on the Lewis acidity of the rutile (1 1 0) surface: A quantum-mechanical simulation of CO adsorption by Jessica Scaranto; Santi Giorgianni (179-183).
The effect of the slab thickness on the Lewis acidity of the rutile (1 1 0) surface has been investigated by quantum-mechanical simulations of the adsorption of carbon monoxide.A systematic study of the effect of the slab thickness on the Lewis acidity of the rutile (1 1 0) surface has been performed by simulating the adsorption of carbon monoxide. The attention has been focused on the molecule–surface distance, the binding and interaction energies and the adsorbed CO stretching frequency. The study shows that converging data, being in good agreement with the experimental ones, are achieved by adopting at least a 12-atomic layers slab and that the use of the possible thinnest slab does not lead to reliable results.
Excited state energy distributions in stereo selective white light emission of 1,2-dibenzthiazolyl ethylene isomers by Mohammad Qureshi; Ziyauddin Khan; S. Sundar Manoharan (184-188).
Photoluminescence based on the energy transfers in the excited states in 1,2-dibenzthiazolyl ethylene stereoisomers are discussed based on time resolved photoluminescence and semi-empirical studies.A detailed study on the influence of stereo specificity, which controls the photo emission characteristics of two dibenzthiazolyl ethylene (DBE) stereoisomers has been carried out using experimental time resolved measurements followed by a configuration interaction semi-empirical calculations. The differences in the photo emission effects are mainly governed by the intra-molecular steric effects, leading to the differences in solid-state packing order having a dihedral angle of ϕ ∼ 40° in cis form and ϕ ∼ 177° in the trans form, more importantly, differences in the intra-molecular electron density distribution causing ‘charge redistribution’ in the excited state.
Optoelectronic switching of addressable self-assembled monolayer molecular junctions by J.C. Li (189-192).
Reproducible optoelectronic switching and temperature dependence of self-assembled monolayer molecular junctions studied under high vacuum conditions.This Letter reports on the observation of optoelectronic switching in addressable molecular crossbar junctions fabricated using stamp-printing method. The active medium is a self-assembled monolayer softly sandwiched between gold electrodes. The junctions are investigated through current–voltage measurements at varied temperature, which show reversible optoelectronic switching with on/off ratio of three orders of magnitude at 95 K. The switching is independent of both optical wavelength and molecular structure, while it strongly depends on the temperature. It is shown that the distinct binding nature of the molecule/electrode interfaces play a dominant role in the switching performance.
Optimal temperature ladders in replica exchange simulations by Robert Denschlag; Martin Lingenheil; Paul Tavan (193-195).
Round trip rates (solid line) and round trip rate per number of replicas (dashed line) as a function of the average acceptance probability for large constant heat capacities.In replica exchange simulations, a temperature ladder with N rungs spans a given temperature interval. Considering systems with heat capacities independent of the temperature, here we address the question of how large N should be chosen for an optimally fast diffusion of the replicas through the temperature space. Using a simple example we show that choosing average acceptance probabilities of about 45% and computing N accordingly maximizes the round trip rates r across the given temperature range. This result differs from previous analyses which suggested smaller average acceptance probabilities of about 23%. We show that the latter choice maximizes the ratio r / N instead of r.
Theoretical study on the excited states of heteroarene chromophores: Comparison of calculated and experimental values by Toshiyuki Tsuji; Maki Onoda; Yuko Otani; Tomohiko Ohwada; Takahito Nakajima; Kimihiko Hirao (196-200).
The SAC-CI method (S) with the CIS-optimized structure (C) is generally superior to other approaches to calculate emission energies of heteroaromatic chromophores.We compare the absorption/emission energies of three heteroaromatic chromophores, indoles, benzofurazans and coumarins, both experimentally and theoretically. First we used TDDFT and SAC-CI methods to calculate S0 → S1 vertical excitation energies corresponding to the absorptions. The excitation energies obtained by the SAC-CI method were superior to those obtained by the TDDFT method, as well as being consistent with those experimentally obtained. We thus applied the SAC-CI method to estimate the emission energies of these chromophores on the basis of the CIS- or TDDFT-optimized excited-state structures. We found a good and consistent agreement of the CIS-structure-based values with the experimental values, whereas the TDDFT-structure based values showed less good agreement.
Charge-transfer in Symmetry-Adapted Perturbation Theory by Anthony J. Stone; Alston J. Misquitta (201-205).
Omission of exchange effects greatly over-estimates the charge-transfer energy. When corrected for exchange, the charge-transfer energy is small.In Symmetry-Adapted Perturbation Theory the charge-transfer energy is normally absorbed into the induction energy, but it can be treated separately. There are two contributions: the long-range or polarization term, which ignores effects due to exchange of electrons between the interacting molecules, and an exchange term. The sum of the two is much smaller than the polarization term, by up to an order of magnitude. The net contribution to hydrogen bond energies is a few kJ mol−1 at equilibrium, and is approximately proportional to the exchange-repulsion energy at other geometries and no more than 10% of it in magnitude.
Comment on ‘To stack or not to stack: Performance of a new density functional for the uracil and thymine dimers’ [Chem. Phys. Lett. 459 (2008) 164] by Tanja van Mourik (206-208).
The apparent existence of this particular stacked uracil dimer on the MP2/6-31+G(d) surface is entirely due to basis set superposition error.A Letter by Gu et al. [J. Gu, J. Wang, J. Leszczynski, Y. Xie, H.F. Schaefer III, Chem. Phys. Lett. 459 (2008) 164] presented MP2/6-31+G(d) and MP2/TZVPP stacking energies for the uracil and thymine dimers, with the aim to assess the performance of the new M06-2X density functional. However, the stacking energies were not corrected for the basis set superposition error (BSSE). Here we show that correction for this error dramatically changes the results. BSSE correction severely reduces the stacking energy of the thymine dimer, whereas the stacked uracil dimer structure considered by Gu et al. is not even a minimum on the MP2/6-31+G(d) potential energy surface.
Reply to ‘Comment on ‘To stack or not to stack: Performance of a new density functional for the uracil and thymine dimers’ [Chem. Phys. Lett. 459 (2008) 164]’ by Jiande Gu; Jing Wang; Jerzy Leszczynski; Yaoming Xie; Henry F. Schaefer (209-210).
The optimized structures of the uracil dimer (left) and the thymine dimer (right) at M06-2x/DZP++ level.In this Letter, we want to address that the conclusions of the letter by Gu et al. have been misunderstood by Mourik in the comment. In our Letter (CPLETT-08-419R1), the good performance of the new functional M06-2X is concluded based on the comparison with the results based on the CCSD(T) studies. Also, we confirm here our previous assumption related to the nature of the stationary points on the MP2 potential energy surface.
Erratum to ‘p- and n-Type Ba8Ga16Ge30 studied by X-ray photoelectron spectroscopy’ [Chem. Phys. Lett. 472 (2009) 60] by Jun Tang; Ryotaro Kumashiro; Jing Ju; Zhaofei Li; Marcos A. Avila; Kouichirou Suekuni; Toshiro Takabatake; Fangzhun Guo; Keisuke Kobayashi; Katsumi Tanigaki (211).