Chemical Physics Letters (v.469, #1-3)
Editorial Board (IFC).
New insights into catalytic CO oxidation on Pt-group metals at elevated pressures by Sean M. McClure; D. Wayne Goodman (1-13).
Producing a definitive picture of the CO oxidation reaction (CO + O2 → CO2) on Pt-group metals (Rh, Pd, Pt and Ru) across the ‘pressure gap’ has proven a challenging task for surface scientists. New results are presented here across a wide pressure range.Producing a definitive picture of the CO oxidation reaction (CO + O2 → CO2) on Pt-group metals (Rh, Pd, Pt, and Ru) across the ‘pressure gap’ has proved to be a challenging task. Surface-sensitive techniques amenable to high pressure environments (e.g. PM-IRAS) have sparked a renewed interest in this reaction under realistic pressures. Here, we review recent work in our laboratory examining CO oxidation kinetics on Pt-group single crystals using PM-IRAS, XPS, and mass spectrometry from low (10−8–10−3 Torr) to high (1–102 Torr) pressures. These studies have shown that at both low and high pressures (a) Langmuir–Hinshelwood kinetics adequately describe CO oxidation kinetics on Pt-group metals (Pt, Pd, Rh) (i.e. there is no pressure gap) and (b) the most active surface is one with minimal CO coverage. Additionally, recent investigations of high pressure CO oxidation kinetics on SiO2 film supported Rh particles prepared in situ are discussed.
Multiply ionization of benzene clusters by a nanosecond laser: Distributions of the ion charge state and the electron energy by Nazhen Zhang; Weiguo Wang; Huaiwen Cang; Hailong Wang; Haiyang Li (14-18).
The ejected electron energy distribution in the interaction of nanosecond-benzene cluster at laser intensity of 1.4 × 1011 W/cm2.The electron energies were measured to investigate the influences of laser intensity and wavelength on the ion charge state distribution of C q + (q = 2–4) when benzene clusters were irradiated by 109–1011 W/cm2 nanosecond laser pulses. The results show that the ratios of C q +/C( q −1)+ strongly depend on laser wavelength but slightly on laser intensity. The mean electron energy up to 100 eV was measured, which was qualitatively consisted with the ‘multiphoton ionization ignition-inverse bremsstrahlung heating-electron impact ionization’ three-stage model. The screening effects inside clusters can significantly decrease the ionization potentials of C q + and facilitate the formation of multiply charged ions especially at low laser intensity.
Velocity map imaging apparatus applicable to a study of multiple photofragmentation of C60 by Md. Serajul Islam Prodhan; Hideki Katayanagi; Chaoqun Huang; Hajime Yagi; Bhim Prasad Kafle; Koichiro Mitsuke (19-25).
A velocity map imaging spectrometer was constructed for observation of the slow fragment ions with thermal energies produced by photoionization of fullerenes.A velocity map imaging (VMI) spectrometer was constructed for observation of the slow ions produced by photofragmentation of C60 with synchrotron radiation. The spectrometer was tested by observing the ion images of rare gases in the Maxwell–Boltzmann distribution at room temperature, and the effect of a large ionization volume inevitable in our experiment has been quantitatively characterized. Numerical simulations taking into account such instrumental parameters indicate that one can distinguish the two independent formation processes of C 56 + from the primary precursor C 60 + : i.e., one-step ejection of C4 and sequential ejections of two C2 fragments.
Revisiting the potential energy surface for the He + H 2 + → HeH + + H reaction at the full configuration interaction level by C.N. Ramachandran; D. De Fazio; S. Cavalli; F. Tarantelli; V. Aquilanti (26-30).
A new potential energy surface is proposed for the reaction He + H 2 + → HeH + + H using Full configuration interaction method and cc-pVQZ basis set. The root mean square deviation of the fit of this surface is 6 meV making it adequate for further investigations of the dynamics.A new potential energy surface is proposed for the title reaction. Calculations have been carried out using the full configuration interaction method and an extended basis set. The selection of geometries is based on an earlier paper [P. Palmieri et al., Mol. Phys. 98 (2000) 1835], where calculations had been made at MRCI level including all single and double excitations from the CASSCF space. Care was taken in blending the long-range two-body interactions with the short-range three-body contributions, specifically described in a hyperspherical reference frame. A many-body expansion fit is presented, with root-mean-square deviation 6 meV, adequate for further investigations of the dynamics.
Density functional theory calculations of vibrational spectra of rhodium oxide clusters by D.J. Harding; S.R. Mackenzie; T.R. Walsh (31-34).
The predicted infrared spectra for two low-energy isomers of the Rh 6 O 2 + cluster, indicating that unambiguous assignment of these structures via multi-photon dissociation spectroscopy is a strong possibility.Predicted infrared vibrational spectra of low-energy isomers of rhodium cluster oxides, Rh 6 O m + ( m = 1 – 4 ) , are presented, based on structures calculated using density functional theory. The oxygen stretching frequencies are found to be characteristic of the oxygen binding mode. These simulated spectra provide a guide to future experimental measurements of the infrared multi-photon dissociation spectra, enabling assignment of the binding sites of oxygen atoms on the cluster. In favourable cases these calculations suggest that a determination of the underlying metal framework structure is possible.
Observation of the C2H2−N2O van der Waals complex in the overtone range using CW-CRDS by K. Didriche; C. Lauzin; P. Macko; M. Herman; W.J. Lafferty (35-37).
C2H2–N2O band center around 1.5 μm, observed and calculated.A slit nozzle supersonic expansion containing C2H2 (246 sccm) and N2O (355 sccm) seeded into Ar (1260 sccm) is investigated using CW cavity ring-down spectroscopy, in the 1.5 μm range. The C2H2−N2O van der Waals complex is observed around the 2CH acetylenic band. Despite strong perturbations, 117 b-type lines are assigned. Their combined fit with published microwave data leads to new upper state and improved lower state rotational constants. The Lorentzian width of the assigned line profiles sets the mean lifetime to 1.6 ns. The rotational temperature is estimated to be 15 K from the comparison between observed and simulated spectra.
Trends in ns2 np0 [M(CO)]q+ complexes: From germanium to element 114 (Uuq) by C. Gourlaouen; O. Parisel; J.-P. Piquemal (38-42).
Relativistic effects on metal-carbon bond lengths and interaction energies in M–CO complexes.The present contribution reports investigations on the metal-ligand bond lengths and interaction energies in selected carbon monoxide complexes of metal cations sharing the ns2 np0 valence configuration. 1- and 4-component DFT geometry optimizations have been performed for cations ranging from Ge2+ to Uuq2+, the dication of element 114 (Ununquadium). The nature of the bonding has been studied by means of energy decomposition analysis.The magnitude of the relativistic effects is shown to evolve slowly and to become predominant for Uuq for the molecular properties investigated.
Ultrafast dynamics of the S1 excited state of benzene by D.S.N. Parker; R.S. Minns; T.J. Penfold; G.A. Worth; H.H. Fielding (43-47).
Ultrafast radiationless decay from an excited singlet state of benzene to a triplet state (ultrafast intersystem crossing).We investigate the ultrafast intramolecular dynamics of electronically and vibrationally excited benzene using time-resolved photoelectron spectroscopy and quantum dynamics simulations. In addition to an ultrafast initial decay, we observe an oscillation between two states. We interpret this data in terms of excited state population moving away from the Franck–Condon region towards the singlet–singlet conical intersection with the ground-state, where ultrafast intersystem crossing from the initially populated singlet state to an optically dark triplet state is enhanced. Our results challenge the currently accepted view that intramolecular processes in hydrocarbons which involve a change of spin are negligibly slow.
An unconventional halogen bond with carbene as an electron donor: An ab initio study by Qingzhong Li; Yilei Wang; Zhenbo Liu; Wenzuo Li; Jianbo Cheng; Baoan Gong; Jiazhong Sun (48-51).
A new type of halogen bond with carbene as an electron donor has been evaluated.An unconventional halogen bond has been proved to exist in H2C–BrH complex. The halogen bond energy of H2C–BrH complex is calculated at four levels of theory [MP2, MP4, CCSD, and CCSD(T)]. The result shows that the carbene is a better electron donor. The substitution effect is prominent in this interaction. For example, the interaction energy in H2C–BrCN complex is increased by more than 300% relative to H2C–BrH complex. The analyses of NBO, AIM, and energy components were used to unveil the nature of the interaction. The results show that this novel halogen bond has similar characteristics to hydrogen bonds.
Measurement and analysis of rotational lines in the (2ν 1 + ν 2 + ν 3) overtone band of H2O perturbed by CO2 using near infrared diode laser spectroscopy by Priyanka Poddar; Amitava Bandyopadhyay; Debasish Biswas; Biswajit Ray; Pradip N. Ghosh (52-56).
CO2 broadening of water vapor rovibrational transitions belonging to the (2ν 1 + ν 2 + ν 3) overtone band studied by near IR diode laser spectroscopy.We report the CO2-induced broadening coefficients and line strength parameters of water vapor rovibrational transitions belonging to the (2ν 1 + ν 2 + ν 3) overtone band measured by using an NIR diode laser spectrometer. Rotational quantum number dependence of the broadening coefficients is also shown. Use of balanced photodetector and wavelength modulation spectroscopy with small current modulation amplitude helped to obtain improved S/N ratio of the spectra. The recorded line shapes are fitted with standard Voigt profile by using a non-linear least squares fitting program to extract the line shape parameters.
Water-catalyzed gas-phase reaction of formic acid with hydroxyl radical: A computational investigation by Yi Luo; Satoshi Maeda; Koichi Ohno (57-61).
It is computationally found that the water-catalyzed process of this reaction is more kinetically favorable than its non-catalytic process.The reaction of formic acid with hydroxyl radical, which is considered to be relevant to atmospheric chemistry, has been extensively studied. A water-catalyzed process of this reaction is computationally studied here for the first time. The scaled hypersphere search method was used for global exploration of pre-reaction complexes. Calculations were performed at high level of theory, such as CCSD(T)/cc-pVTZ//B3LYP/6-311+G(2df, 2p) and CCSD(T)/cc-pVTZ//MP2/aug-cc-pVDZ. It is found that the water-catalyzed process of this reaction is more kinetically favorable than its non-catalytic process. Such catalytic process may also be of interest for atmospheric chemistry, like the non-catalytic one.
Ground and low-lying excited states of Na(NH3) n and Na(H2O) n clusters: Formation and localization of solvated electron by Kenro Hashimoto; Kota Daigoku (62-67).
Theoretical calculations show that an unpaired electron is localized at a faster rate against n in Na(H2O) n than in Na(NH3) n .The ground and low-lying excited states of Na(NH3) n and Na(H2O) n (n = 1–8) clusters were studied using ab initio molecular orbital methods. The calculated vertical transition energies to the 32P(Na)-type states agree well with the energies of the absorption maxima. The clusters change from a valence state to a two-center state via a diffuse one-center state with increasing n in both the ground and excited states. The localization of an unpaired electron proceeds at a faster rate against n in Na(H2O) n than in Na(NH3) n . The formation of an excited state of the solvated electron is found in Na(H2O)4–8.
Surface-catalyzed singlet oxygen production on iodine oxide films by Seonkyung Lee; W. Terry Rawlins; Steven J. Davis (68-70).
Catalytically enhanced singlet oxygen production.Enhanced production of singlet oxygen, O2(a 1Δg), was observed by reaction of O2/He discharge effluents on an iodine oxide film surface in a microwave discharge-flow reactor at 320 K. We observed a two-fold increase in the O2(a) yields over discharge-generated amounts for non-catalytic conditions. The iodine oxide surface appears to catalyze the heterogeneous reaction to form O2(a) with high collision efficiency. The observed catalytic effect could significantly benefit the development of electrically driven oxygen–iodine laser systems, and may also have implications for the chemistry of atmospheric iodine oxide aerosol.
Solvation dynamics of a surfactant probe in mesostructured silica-surfactant nanocomposites by A. Paul; M. Sarkar; D.C. Khara; T. Kamijo; A. Yamaguchi; N. Teramae; A. Samanta (71-75).
Involvement of constrained water molecules in the solvation dynamics of a surfactant probe incorporated in mesostructured silica-surfactant nanocomposites is demonstrated.Steady-state and time-resolved fluorescence behavior of a 4-aminophthalimide-based surfactant probe has been studied in a mesostructured silica-surfactant nanocomposite. While the steady-state measurements indicate the location of the probe in the nanocomposite, the time-resolved study reveals the distinctive features of the solvation dynamics of the probe. Comparison of the present dynamical data with those reported for the parent fluorophore in other organized assemblies suggests the involvement of constrained water molecules near the ionic interface in the observed dynamics.
Diffusion-mediated electron transfer between cations in ionic solutions monitored by fluorescence quenching by M. Hilczer; M. Steblecka; M. Wolszczak; M. Tachiya (76-80).
Calculated and experimental ionic strength dependence of the diffusion-mediated quenching rate constant associated with electron transfer between cations in solution.The diffusion-mediated quenching rate constant kq associated with photoinduced electron transfer (ET) reaction between cations in aqueous solutions containing inert electrolyte was theoretically studied by using the modified Tachiya–Murata theory [J. Phys. Chem. 96 (1992) 8441]. The ET was assumed to occur not only at the contact distance R between the reactants but over a range of distances r > R. The calculated kq and its dependence on the ionic strength are in reasonable agreement with experimental values obtained from the single-photon counting measurements on the system 9-anthrylmethylammonium cation donor (D+)–methylviologen cation acceptor (A2+).
Theoretical study on kinetics of the H2CO + O2 → HCO + HO2 reaction by Lam K. Huynh; Max Tirtowidjojo; Thanh N. Truong (81-84).
A direct ab initio dynamics study on the O2 + H2CO → HO2 + HCO reaction has been carried out from first principles using canonical variational transition state theory incorporating corrections from small curvature tunneling and hindered rotation treatments. Rate constants were calculated using the geometries, gradient and Hessian obtained at the BH&HLYP/cc-pVDZ level with the energy correction at the CCSD(T)/aug-cc-pVTZ//BH&HLYP/cc-pVDZ level. The rate constant expression is obtained as k ( t ) = 2.95 × 10 - 21 × T 3.152 × exp - 18 352 T (cm3 molecule−1 s−1) for the temperature range 300–3000 K. The result shows an excellent agreement with available scattered experimental data over this temperature range and thus the expression can be used confidently for the whole range.A theoretical study on the kinetics of the H2CO + O2 → HCO + HO2 reaction has been carried out from first principles using canonical variational transition state theory incorporating corrections from small curvature tunneling and hindered rotation treatments. Rate constants were calculated using the geometries, gradient and Hessian obtained at the BH&HLYP/cc-pVDZ level with the energy correction at the CCSD(T)/aug-cc-pVTZ//BH&HLYP/cc-pVDZ level. The rate constant expression is obtained as k ( t ) = 2.95 × 10 - 21 × T 3.152 × exp - 18 352 T (cm3 molecule−1 s−1) for the temperature range 300–3000 K. The result shows an excellent agreement with available scattered experimental data over this temperature range and thus the expression can be used confidently for the whole range.
The C–H⋯π interaction in the halothane/ethene complex: A cryosolution infrared and Raman study by Johan J.J. Dom; Bart Michielsen; Bert U.W. Maes; Wouter A. Herrebout; Benjamin J. van der Veken (85-89).
A complex between halothane and ethene has been studied using infrared and Raman spectroscopy, supported by quantum mechanical calculations.The formation of a C–H⋯π bonded complex between halothane, CF3CHBrCl, and ethene has been studied in liquid krypton in the temperature range between 119 and 143 K, using infrared and Raman spectroscopy. The standard complexation enthalpy of the 1:1 complex was measured to be −5.0(2) kJ mol−1. The stretching mode of the C–H bond involved in the formation of the complex was observed to red shift by 7.2(1) cm−1, while its intensity increased by a factor of 2.1(2). The results are compared with ab initio calculations at the MP2/6-311++G(d,p) and MP2/aug-cc-PVXZ (X = D, T and Q) levels.
An incremental coupled-cluster approach to metallic lithium by Hermann Stoll; Beate Paulus; Peter Fulde (90-93).
Pair energies for localized orbitals in finite clusters are used for an estimate of the cohesive energy of bulk lithium.Coupled-cluster pair energies calculated for localized orbitals in finite lithium clusters are used for an estimate of the cohesive energy and the lattice constant of the bcc lithium crystal. It is shown that the results converge reasonably fast with cluster size and are of comparable quality with conventional density functional ones for the infinite solid.
Partially polarized fluorescence emitted by MEHPPV in solution by P. Alliprandini-Filho; R.A. da Silva; N.M. Barbosa Neto; A. Marletta (94-98).
This work regards on the study of polarized state of MEHPPV in solution. A unexpected partially polarized fluorescence is observed being caused by a steady regime where light is absorbed and reemitted faster than the average molecular diffusion time.This work reports on the use of the ellipsometry technique to study the polarization state of emitted light by poly[2-methoxy-5-((2′-ethylhexyl)oxy)-1,4-phenylenevinylene] (MEHPPV) in solution. The sample presents a partially linear-polarized fluorescence not affected by molecular-concentration, excitation-laser power, probe-wavelength and cuvette-material. The independence of the polarization degree with these variables and its variation with solvent viscosity suggest that the effect can be understood, assuming the existence of a steady regime where light is absorbed and reemitted faster than the average molecular diffusion time. Moreover, we verified that the polarized emission is also observed by other polymers in solution.
The transition from metal–metal bonding to metal–solvent interactions during a dissolution event as assessed from electronic structure by Christopher D. Taylor (99-103).
Density functional theory calculations show that dissolving metal atoms transition from metal/metal to metal/solvent bonding within 0.1 nm.A model for the electrochemical interface appropriate to the simulation of metal atom deposition and dissolution processes using electronic structure methods has been constructed and analyzed to observe the key steps governing the movement of a metal atom across the electrochemical double layer. A transition from metal–metal bonding to metal–solvent bonding occurs at a distance of 1 Å. Shortcomings in this model are assessed and related to the difficulty of dynamical sampling in ab initio treatments. The model is shown to provide a flexible basis for understanding the effect of system perturbations to the structure of the dissolution potential energy surface.
Molecular structure-property correlations from optical nonlinearity and thermal-relaxation dynamics by Indrajit Bhattacharyya; Shekhar Priyadarshi; Debabrata Goswami (104-109).
A molecular structure-property relationship is established from the variation of third-order nonlinear susceptibility and thermal-diffusivity for a primary alcohol series.We apply ultrafast single beam Z-scan technique to measure saturation absorption coefficients and nonlinear-refraction coefficients of primary alcohols at 1560 nm. The nonlinear effects result from vibronic transitions and cubic nonlinear-refraction. To measure the pure total third-order nonlinear susceptibility, we removed thermal effects with a frequency optimized optical-chopper. Our measurements of thermal-relaxation dynamics of alcohols, from 1560 nm thermal lens pump and 780 nm probe experiments revealed faster and slower thermal-relaxation timescales, respectively, from conduction and convection. The faster timescale accurately predicts thermal-diffusivity, which decreases linearly with alcohol chain-lengths since thermal-relaxation is slower in heavier molecules. The relation between thermal-diffusivity and alcohol chain-length confirms structure-property relationship.
On the use of Z-scan fluorescence correlation experiments on giant unilamellar vesicles by Ellen Gielen; Martin vandeVen; Anca Margineanu; Peter Dedecker; Mark Van der Auweraer; Yves Engelborghs; Johan Hofkens; Marcel Ameloot (110-114).
Fluorescence correlation spectroscopy at multiple focus planes (Z-scan FCS) is applied to giant unilamellar vesicles in the electroformation chamber. Z-scan fluorescence correlation spectroscopy (FCS) uses multiple focus planes to determine diffusion coefficients in supported phospholipid bilayers (SPBs) without the need for extrinsic calibration. The approach can be used to discriminate diffusion modes. In this work, Z-scan FCS was applied to study the diffusion of the fluorescent lipid analogue DiI–C18(5) in the top membrane of giant unilamellar vesicles (GUVs) in the electroformation chamber. In contrast to SPBs, the intrinsic estimate of the radial waist might differ from the one obtained by extrinsic calibration. We describe a pragmatic approach to verify the validity of the Z-scan approach under these conditions.
Entropic effects in excited state CT reactions by A. Pigliucci; E. Vauthey; W. Rettig (115-120).
The large amplitude motion connected with CT formation in DMABN is controlled by the activation entropy (the Arrhenius prefactor). A possible explanation is a conical intersection necessitating a two-dimensional description of the reaction.The kinetics of the dual fluorescence of several derivatives of dimethylaminobenzonitrile (DMABN) has been compared using fs-fluorescence upconversion experiments. Variation of the size and twist angle of the donor (dialkylamino group) suggest a large amplitude solvent-viscosity controlled diffusional twisting motion towards larger twist angles as the rate limiting step.Large rate differences were observed for an ester group as acceptor. Temperature dependent studies indicate that these differences are not connected with different activation barriers but with changes in the Arrhenius preexponential factor. It is argued that conical intersections along the reaction path can bring about these entropy changes.
Full electronic excitation spectrum of condensed manganese phthalocyanine by R. Kraus; M. Grobosch; M. Knupfer (121-124).
A low lying excitation at 0.5 eV has been identified in manganese phthalocyanine films.The electronic excitation spectrum of manganese phthalocyanine films has been studied using a combination of optical absorption and electron energy-loss spectroscopy. These studies reveal the existence of a low lying excitation at 0.5 eV, which has not been identified previously. These excitations are localized and have a predominant dipole allowed character. Most likely, they arise from transitions between states which have a ligand as well as manganese metal character.
Influence of metal coating on single-walled carbon nanotube: Molecular dynamics approach to determine tensile strength by Shuhei Inoue; Yukihiko Matsumura (125-129).
The rupture phenomenon of metal-coated SWCNT is compared with uncoated SWCNT by molecular dynamics simulation.The physical strength of a metal-coated single-walled carbon nanotube (SWCNT) is derived in terms of a stress–strain curve by molecular dynamics simulation. The breaking stress of a metal-coated SWCNT was lower than that of an uncoated SWCNT; however, the force constant increased by 17%, which can be attributed to the effect of the metal coating on the SWNCT. With regard to the rupture phenomena, it was observed that the uncoated SWCNT yielded more easily than the metal-coated SWCNT at the yield point. The rupture phenomenon was initiated by a local distortion of the metal atoms of the SWCNT.
Tracing exciton dynamics in molecular nanotubes with 2D electronic spectroscopy by Alexandra Nemeth; Franz Milota; Jaroslaw Sperling; Darius Abramavicius; Shaul Mukamel; Harald F. Kauffmann (130-134).
Energy transfer pathways monitored by two-dimensional electronic spectroscopy.Identifying the pathways and timescales of excitation energy transfer is a central goal in the design of artificial light harvesting systems and energy transporting wires. Coherent femtosecond two-dimensional electronic spectroscopy provides this information for a molecular nanotube by correlating excitonic absorption and emission frequencies at various delay periods. In combination with simulations based on a coupled electronic oscillator model the experiments reveal the electronic coupling pattern and show the various energy transfer pathways into the lowest accessible state.
Quantitative structural relationship and theoretical study of electrochemical properties of C60@[SWCN(5, 5)-Armchair-C n H20] complexes by Avat Arman Taherpour (135-139).
The relationship between this index and electron affinity; the reduction potential ( RedE) of [SWCN(5, 5)-Armchair-C n H20] 1–18 and 19–29; and the free energy of electron transfer (ΔG et) as assessed using the Rehm–Weller equation between 1–18 and fullerene C60 as C60@[SWCN(5, 5)-Armchair-C n H20] 30–47 and 48–58 complexes, are presented.Nanoscale structures of carbon display an attractive variation of structural characteristics, and many useful forms have been synthesized and identified. One of these structures is the carbon nanotubes. Carbon nanotubes are either single-wall (SWCNT) or multi-wall; the former attract more attention due to their unique electronic, optical and spectroscopic properties. The electrochemical properties of the fullerene C60 have been studied previously. The accommodation of C60 inside the SWCNT leads to significant periodic modifications of the electronic states of SWCNT. One of the main recognized structures of nanotubes is the (5, 5) single-wall tube (SWCN). A topological index is a mathematical invariant of a chemical graph, which shows a significant correlation with some chemical or physical property. They have been successfully used to construct effective and useful mathematical methods for finding good relationships between structural data and the properties of these materials. To establish a good structural relationship between the structure of molecules C60 and [SWCN(5, 5)-Armchair-C n H20] (n = 20–190) 1–18, the molecular degree of unsaturation (DU ) was used as one of the useful numerical and structural electrochemical properties of unsaturated compounds. In this study, the relationship between this index and electron affinity; the reduction potential ( RedE) of [SWCN(5, 5)-Armchair-C n H20] 1–18 and 19–29; and the free energy of electron transfer (ΔG et) as assessed using the Rehm–Weller equation between 1–18 and fullerene C60 as C60@[SWCN(5, 5)-Armchair-C n H20] 30–47 and 48–58 complexes, are presented.
DFT study of molybdena–silica system – A selection of density functionals based on their performance in thermochemistry of molybdenum compounds by Jarosław Handzlik (140-144).
Assessment of DFT methods for molybdenum thermochemistry–an application of selected functionals in studies of Mo(VI) species on silica.Accuracy of 22 DFT methods in predicting the energetics of test reactions involving MoO2(g), MoO3(g), MoO2(OH)2(g) and MoO2Cl2(g) is studied. Experimental heats of formation and CCSD(T) energies are used as the reference data. The most precise methods appear TPSS, PW91, PBE, M05, TPSSKCIS and BP86.Selected density functionals are then applied in investigations of isolated monooxo and dioxo Mo(VI) species on the silica surface. For the molybdena–silica models proposed in this work, the monooxo form is predicted to be more stable under dehydrated conditions than the dioxo species, irrespective of the DFT method used.
First-principles study of the B- or N-doping effects on chemical bonding characteristics between magnesium and single-walled carbon nanotubes by Kunpeng Wang; Chunsheng Shi; Naiqin Zhao; Xiwen Du; Jiajun Li (145-148).
B-doping increases dramatically the binding energy of single Mg atom on both armchair and zigzag SWCNTs.We investigated theoretically the adsorption of individual Mg atoms on single-walled carbon nanotubes (SWCNTs) by first-principles method within density functional theory in order to clarify the binding energies and the electronic structures of Mg atoms contact with SWCNTs. Our results suggest that the interaction of Mg atom adsorbed on pristine SWCNTs, which is normally very weak, can be enhanced upon functionalization of SWCNTs by B- or N-doping. Especially, the B-doping increases dramatically the binding energies of Mg-adsorbed on both armchair and zigzag SWCNTs.
Surface charge induced Stark effect on luminescence of quantum dots conjugated on functionalized carbon nanotubes by W. Wang; G.K. Liu; H.S. Cho; Y. Guo; D. Shi; J. Lian; R.C. Ewing (149-152).
Stark effect of QDs conjugated on functionalized CNTs induced by the electrostatic field of carboxylic anions on the CNT surface.A significant blue shift of the luminescence of CdSe/ZnS quantum dots (QD) conjugated with functionalized multi-wall carbon nanotubes (CNT) is investigated. The observed Stark shift is due to the local electrostatic field induced by the carboxylic anions on the CNT surface. A theoretical model is developed to evaluate the contribution of the surface charges to the observed spectral shift (up to 0. 59 eV). Based on the present model, the Stark shift provides an effective method for evaluating the density of carboxyl groups on the surface of functionalized CNTs and can be used as a charge detector for QD–nanostructures.
Interaction of • CH2OH with silver cation in Ag–A/CH3OH zeolite: A DFT study by Marek Danilczuk; Dariusz Pogocki; Anders Lund (153-156).
Density functional theory (DFT) has been applied to model the structure of (Ag • CH2OH/A)+ complexes previously experimentally characterized by electron paramagnetic resonance (EPR) in zeolite matrices. The magnetic parameters of (Ag • CH2OH/A)+ were found to depend on the local structure of the zeolite represented by clusters referred to as 3T and 6T, and also on the applied computational method. A spin distribution analysis confirms the one-electron silver–carbon bonding, showing delocalization of an unpaired electron density distributed between the sliver and carbon atoms along the one-electron silver–carbon bond. The results are of relevance for a deeper understanding of the electronic and catalytic properties of zeolites containing silver atoms and clusters.Density functional theory (DFT) has been applied to model the structure of (Ag • CH2OH/A)+ complexes previously experimentally characterized by electron paramagnetic resonance (EPR) in zeolite matrices. The magnetic parameters of (Ag • CH2OH/A)+ were found to depend on the local structure of the zeolite represented by clusters referred to as 3T and 6T, and also on the applied computational method. A spin distribution analysis confirms the one-electron silver–carbon bonding, showing delocalization of an unpaired electron density distributed between the sliver and carbon atoms along the one-electron silver–carbon bond. The results are of relevance for a deeper understanding of the electronic and catalytic properties of zeolites containing silver atoms and clusters.
Thermodynamic symptom of coexistence of two aggregation modes in the Im3m cubic phase formed in thermotropic mesogen, ANBC(n) by Kazuya Saito; Tadahiro Nakamoto; Michio Sorai; Haruhiko Yao; Kenji Ema; Kunio Takekoshi; Shoichi Kutsumizu (157-160).
The alkyl chain-length dependence of heat capacity supports the complex structural model of the liquid crystal with Im3m symmetry.The heat capacities of two members of a representative cubic mesogen, 4′-alkoxy-3′-nitrobiphenyl-4-carboxylic acid, were measured precisely. In accordance with the tendency reported previously for other members, the heat capacity in the cubic phase is smaller than that in the neighboring smectic C phase. The chain-length dependence of the reduction in the heat capacity upon the phase transition showed opposing trend depending on symmetry of the cubic phase (Ia3d or Im3m). This finding is rationalized by assuming the existence of two aggregation modes (rod and shell) in the Im3m phase in contrast to only the former mode in the Ia3d phase.
High resolution probing of multi wall carbon nanotubes by Tip Enhanced Raman Spectroscopy in gap-mode by Gennaro Picardi; Marc Chaigneau; Razvigor Ossikovski (161-165).
Intensity of the tip-enhanced Raman signal in the frequency region 1470–1660 cm−1 recorded across two multi wall carbon nanotubes.We present Tip Enhanced Raman Spectroscopy (TERS) results with side illumination of a scanning tunneling microscope (STM) Au tip on thin multi wall carbon nanotubes deposited on Au(1 1 1) with a ∼75 nm lateral resolution. The spectral features observed in the enhanced near-field regime are discussed considering also the presence of defects in the tube(s) structure and/or trace amounts of amorphous carbon contaminations.
Cr/Sb co-doped TiO2 from first principles calculations by Cristiana Di Valentin; Gianfranco Pacchioni; Hiroshi Onishi; Akihiko Kudo (166-171).
Density functional study of Cr/Sb co-doped TiO2 system for improving photo-activity in the visible region.Co-doping of TiO2 with Cr and Sb was recently found to have a beneficial effect on the photocatalytic activity under visible-light irradiation. With the present comparative standard and hybrid density functional study we get new insight into the electronic structure of the system and provide a theoretical support to the experimental findings. Hybrid DFT better describes (i) the Cr d states splitting and thus the semiconducting properties of the Cr-doped system, and (ii) the localized nature of the Ti3+ states produced by Sb doping. An electron transfer from the Sb-induced states to the Cr 3d levels is considered to be the reason for the enhanced photostability of the co-doped Cr/Sb system.
Nonlinear polarization effects in superchiral nanotube sensors of amino acids by D. Vardanega; C. Girardet (172-176).
Carbon nanotube sensors, enantioselectivity of amino acids, superchirality, non linear polarization.We develop a theoretical model showing that insertion of a polar and polarizable α-helix in a chiral carbon nanotube, used in resonator configuration, substantially improves the enantiospecific detection of chiral molecules. The differential resonance frequency shift associated with the adsorption of the two alanine enantiomers is calculated to increase by about 50% when compared to the response of the tube alone at the linear polarization approximation, and up to 100% when nonlinear polarization effects are taken into account.
Thermal stability studies of CVD-grown graphene nanoribbons: Defect annealing and loop formation by J. Campos-Delgado; Y.A. Kim; T. Hayashi; A. Morelos-Gómez; M. Hofmann; H. Muramatsu; M. Endo; H. Terrones; R.D. Shull; M.S. Dresselhaus; M. Terrones (177-182).
A thermal stability study of graphene nanoribbons annealed up to 2800 °C is presented. We noted a progressive annihilation of lattice defects as the heat treatment temperature is raised. Single and multiple loop formation were observed on the ribbons edges as the temperature increases.We present a high temperature heat treatment study of CVD-grown graphene nanoribbons annealed up to 2800 °C, demonstrating a progressive annihilation of lattice defects as the heat treatment temperature is raised. Starting at 1500 °C, single and multiple loop formation were observed on the ribbons edges as the temperature was increased. The structural changes of the samples are documented by X-ray diffraction, Raman spectroscopy, TGA, SEM, and HRTEM. This work indicates that nanoribbon annealing eventually leads to defect-free samples, through graphitization and edge loop formation. The annealed material exhibits structural differences that could be tailored for a variety of specific applications.
First principle studies of zigzag AlN nanoribbon by A.J. Du; Z.H. Zhu; Y. Chen; G.Q. Lu; Sean C. Smith (183-185).
Band structure for a 10-AlN zigzag nanoribbon under the response of external electric field (E = 0.4 V/Å) and spin-up and spin-down density of state plot for a 10-AlN zigzag nanoribbon with N edge unsaturated.Ab initio density functional calculations were performed to study the geometry and electronic structure of a prototypical zigzag AlN nanoribbon. We find that H-terminated zigzag 10-AlN nanoribbons have a non-direct band gap and are nonmagnetic. When a transverse electric field is applied, the band gap decreases monotonically with the strength of field E. Zigzag AlN nanoribbons with the N edge unpassivated display strong spin-polarization close to the Fermi level, which will result in spin-anisotropic transport. These results suggest potential applications for the development of AlN nanoribbon-based nanoelectronics applications.
The origin of the molecular interaction between amino acids and gold nanoparticles: A theoretical and experimental investigation by Frank N. Crespilho; Francisco C.A. Lima; Albérico B.F. da Silva; Osvaldo N. Oliveira; Valtencir Zucolotto (186-190).
This study describes the fabrication of novel biological hybrid materials, where 3D structured material was obtained using gold nanoparticles and methionine. Theoretical and experimental studies show that the bionanomaterial is formed due to the reorientation of methionine molecules with H-bonds between backbone amine groups.This study describes the synthesis of novel biological hybrid materials, where 3D structures were obtained using gold nanoparticles (AuNps) and methionine (Met) in a one-step procedure in aqueous media. The type of nanostructure can be controlled by tuning the intermolecular interactions between Met and AuNp, which strongly depends on the pH used for the synthesis. Computational simulation using the density-functional theory (DFT) showed that the AuNp–Met 3D structures are formed upon reorientation of Met molecules so that the backbone amine groups interact via H-bonds. These findings were experimentally confirmed using FTIR and UV–vis spectroscopy.
Artificial color tuning of firefly luminescence: Theoretical mutation by tuning electrostatic interactions between protein and luciferin by Naoki Nakatani; Jun-ya Hasegawa; Hiroshi Nakatsuji (191-194).
Arg223Ala, Glu344Ala, and Asp422Ala mutations in the firefly oxyluciferase of Photinus pyralis, which could change the luminescence color into reddish-orange.Electrostatic interactions between firefly oxyluciferin and the surrounding proteins were analyzed, and the amino acids important for controlling emission energy were identified. We propose Arg223Ala, Glu344Ala, and Asp422Ala mutations in firefly oxyluciferase of Photinus pyralis, which artificially change the luminescence color by tuning the electrostatic effect from the luciferase proteins. In the theoretical mutation simulation, the emission energy of the triple mutant was estimated to be 2.05 eV (602 nm, reddish-orange), which is 0.18 eV lower than that of the wild type (2.23 eV, 557 nm, yellow–green). For calculating the emission energies, we used the symmetry-adapted cluster-configuration interaction (SAC-CI) method.
Piezotropic unfolding of lysozyme in pure D2O at the outer edge of excess hydration by Helge Pfeiffer; Karel Heremans; Martine Wevers (195-200).
Piezotropic unfolding of lysozyme was studied at relatively low hydration degree.This Letter reports a FTIR study on the pressure-induced unfolding of lysozyme in pure D2O close to the conditions of non excess hydration. An essential population of the proteins apparently refold into its native structure after pressure release. It could furthermore be shown that down to a hydration of h = 2 (h = m prot/ m D 2 O ; m = mass), the unfolding pressure did not vary with hydration. Hydration dependent behaviour was found with respect to the change of the wavenumbers of the α-helical structure during unfolding. This result is discussed with respect to the reversibility of unfolding in pure solvents and with the effects of hydrogen exchange.
Stability and molecular dynamics of chloroxylenol (API of antiseptics and drugs) in solid state studied by 35Cl-NQR spectroscopy and DFT calculations by J.N. Latosińska; M.A. Tomczak; J. Kasprzak (201-206).
The polycrystalline sample of 4-chloro-3,5-dimethyl-phenol (chloroxylenol) in solid state was studied in the temperature range 77–353 K by 35Cl-NQR spectroscopy and DFT calculations.Thermal stability of 4-chloro-3,5-dimethyl-phenol (chloroxylenol) in solid state has been studied by 35Cl-NQR spectroscopy. Two NQR resonance lines at the frequencies 34.348 and 34.415 MHz at 77 K have been assigned to chlorine atoms from two crystallographically inequivalent molecules on the basis of the B3LYP/6-311++G∗∗ results. The temperature dependence of the resonance frequency and full width at half maximum suggest the occurrence of small-angle torsional oscillations of the mean activation energy of 3.83 kJ/mol and rotation of both methyl groups around their symmetry axis C3 with the activation energies 12.49 and 11.27 kJ/mol for CH3 in molecule A and B, respectively. B3LYP/6-311++G∗∗ method reproduced very well the activation energies of both motions.
Fullerene (C60) forms stable complex with nucleic acid base guanine by M.K. Shukla; Jerzy Leszczynski (207-209).
Interaction of C60 with guanine was investigated. ONIOM(MP2/6-31G(d):B3LYP/6-31G(d)) was found to be the most cost-effective approach for such investigation.Interaction of C60 with nucleic acid base guanine was investigated at the DFT-B3LYP, MP2 and ONIOM(MP2:B3LYP) levels of theory using the 3-21G(d), 6-31G(d) and 6-31G(d,p) basis sets. It was found that C60 forms a stable complex with guanine through stacking interaction with binding energy of 8.1 kcal/mol at the MP2/6-31G(d) level. The ONIOM(MP2/6-31G(d):B3LYP/6-31G(d)) approach was found to be the most cost-effective method for such investigation. Neither the B3LYP method nor MP2 level with smaller basis set such as 3-21G(d) are found suitable for such investigation.
Diffusion scaling through structural templates given by the 3d dynamic Ising model by C.-L. Chen; Y. Shapir; E.H. Chimowitz (210-213).
Scaling of mean square displacement data in dynamic percolation systems at infinite temperature.We present new results describing diffusion through networks exhibiting dynamic disorder where diffusion ‘pathways’ are found from dynamic structures obtained from kinetic Monte Carlo (KMC) computer simulations consistent with Kawasaki dynamics in the 3d Ising lattice model.Our simulation results for the diffusion/conductance scaling exponent s are in excellent accord with the most widely quoted theoretical value s = 2 ν - β , where ν and β are 3d static percolation exponents in cubic lattices. This is in contrast to experimentally obtained values for this scaling exponent where there appears to be substantial disparity between many of these prior published results.
Implementation of the CCSD(T)(F12) method using numerical quadratures by Denis Bokhan; Stephan Bernadotte; Seiichiro Ten-no (214-218).
Coupled-cluster diagrams in the Λ-correction contributing to the difference of MP2F12/B and MP2-F12/B∗.We implemented the linear explicitly correlated coupled-cluster singles and doubles with perturbative triples method, using cusp conditions along with the hybrid numerical quadrature (QD) and the resolution of the identity (RI) approach. Furthermore, we outline the connection of this method with many-body perturbation theory. Numerical results obtained with the QD/RI-based method show a faster convergence towards the basis set limit than the corresponding RI-based method. We performed benchmark calculations for a set of 13 chemical reactions.
Substituent effects in the mechanism of mono-substituted acetylene trimerization: A topological analysis of the electron localization function by Oscar Donoso-Tauda; Arie Aizman; Carlos A. Escobar; Juan C. Santos (219-223).
The mono-substituted acetylenes trimerization has been studied using the electron localization function (ELF). Six domains of structural stability of ELF were identified along the reaction path and the substituent effects were characterized in each domain.The reaction mechanism of the mono-substituted acetylenes trimerization has been analysed by means of the electron localization function (ELF). The trimerization reactions were characterized in six domains of structural stability of ELF along the IRC pathway. Substituent effects are shown to be varied and important along the IRC. Among the substituent considered in this study (F, CN, COH and OH), Formyl, the most relevant, promotes reactant stabilization by hydrogen interaction, decreases close shell interactions, increases the distortion energy in the first step, and provides the highest stabilization by aromaticity.
Photoexcitation of 11-Z-cis-7,8-dihydro retinal and 11-Z-cis retinal: A comparative computational study by Ryan R. Zaari; Stephanie Y.Y. Wong (224-228).
HOMO → LUMO transition character of the retinal derivative 11-Z-cis-7,8-dihydro retinal indicates large charge transfer from six-membered ring to polyene chain, not characteristic of native retinal.We present vertical excitation properties calculated using Time-Dependent Density Functional Theory (TD-DFT) and Resolution of Identity second-order coupled cluster (RI-CC2) methods for the lowest energy states of 11-Z-cis retinal and the recently synthesized 11-Z-cis-7,8-dihydro retinal. Within 11-Z-cis retinal the lowest expected energy transition is from the HOMO (π) to LUMO (π ∗), which results in the known isomerization. Contrary to 11-Z-cis retinal, the lowest energy transition within 11-Z-cis-7,8-dihydro retinal possesses some charge transfer character, and it is in fact the second lowest energy excitation from HOMO−1 (π) to LUMO (π ∗) which could lead to the experimentally observed isomerization.