Chemical Physics Letters (v.515, #1-3)
Editorial Board (IFC).
Infrared spectrum of mass-selected CH3S radicals investigated with infrared + vacuum ultraviolet photoionization by Hui-Ling Han; Lung Fu; Yuan-Pern Lee (1-6).
Display Omitted► We applied the (1 + 1) IR-VUV photoionization method to obtain the IR spectrum of the CH3S radical in the range 2780–3270 cm−1. ► With the advantage of the mass-selective detection, the IR spectrum of CH3S shows absorption bands with no interference from the precursor. ► Our results provide direct evidence for the assignments of ν 1 and ν 4 modes of gaseous CH3S.We present a detailed spectral study of the atmospherically important methylthio (CH3S) radical demonstrating the advantage of IR-VUV photoionization for vibrational spectroscopy of free radicals due to its mass selectivity. Photolysis of CH3SH produced CH3S radicals that were ionized with (1 + 1) IR-VUV photoionization and detected with the time-of-flight technique. The IR spectrum of CH3S was obtained in the range 2790–3270 cm−1. Absorptions features near 2819 and 2904 cm−1 are assigned to ν 1 and ν 4 modes of CH3S, respectively, and those near 2978 and 3241 cm−1 are tentatively assigned as combination transitions 315161(e) and 315161(a), respectively, from the ground vibrational state.
Raman and IR spectra of butane: Anharmonic calculations and interpretation of room temperature spectra by Liat Pele; Jiří Šebek; Eric O. Potma; R. Benny Gerber (7-12).
Comparison of first-principles vibrational calculations with IR and Raman experiments for butane.Display Omitted► VSCF calculations closely reproduce IR and Raman experiments for butane. ► B3LYP is superior to MP2 for butane by the test of spectroscopy. ► Anharmonic effects in the CH band spectra are very large. ► Vibrational degeneracy effects in butane are washed out by broadening.First-principles anharmonic calculations are carried out for the IR and Raman spectra of the C―H stretching bands in butane. The calculations use the Vibrational Self-Consistent Field (VSCF) algorithm. The results are compared with gas-state experiments. Very good agreement between the computed and experimental results is found. Theory is successful also in computing a weak peak which is caused by combination transitions. The B3LYP potential surface is found superior to MP2, though both methods give good accord with experiment. The theoretical results provide an understanding of the role of different modes in the spectra of hydrocarbons.
Towards a converged barrier height for the entrance channel transition state of the N(2D) + CH4 reaction and its implication for the chemistry in Titan’s atmosphere by Chanda-Malis Ouk; Natalia Zvereva-Loëte; Béatrice Bussery-Honvault (13-18).
Display Omitted► Highly correlated ab initio methods confirm the existence of a potential barrier in the N(2D) + methane reaction. ► We suggest a barrier height of 3.86 ± 0.84 kJ/mol for the entrance transition state of the N(2D) + methane reaction. ► MS-MR-SDCI method corrected for SCE and BSSE has been used in present work.The N(2D) + CH4 reaction appears to be a key reaction for the chemistry of Titan’s atmosphere, opening the door to nitrile formation as recently observed by the Cassini–Huygens mission. Faced to the controversy concerning the existence or not of a potential barrier for this reaction, we have carried out accurate ab initio calculations by means of multi-state multi-reference configuration interaction (MS-MR-SDCI) method. These calculations have been partially corrected for the size-consistency errors (SCE) by Davidson, Pople or AQCC corrections. We suggest a barrier height of 3.86 ± 0.84 kJ/mol, including ZPE, for the entrance transition state, in good agreement with the experimental value. Its implication in Titan’s atmopsheric chemistry is discussed.
Effect of thermally activated dynamics on electron spin–lattice relaxation in glasses by Dalibor Merunka; Marina Kveder; Boris Rakvin (19-22).
Display Omitted► We study mechanisms of spin–lattice relaxation of paramagnetic centers in glasses. ► Mechanism of thermally activated dynamics of double-well systems is reexamined. ► We use soft-potential model to find temperature dependence of relaxation rate. ► Predicted dependence is similar with those measured in various amorphous materials. ► This mechanism can explain excess of relaxation rate in glassy ethanol.Thermally activated dynamics of double-well systems is reexamined as a possible mechanism of electron spin–lattice relaxation (SLR) of paramagnetic centers in glasses. Using the soft-potential model, we have found that this mechanism can explain a nearly quadratic temperature dependence of the SLR rate in various amorphous materials over the temperature range 1–100 K. This mechanism is expected to be operative over this temperature range, as opposed to the phonon-induced tunneling of two-level systems, which is usually considered as the mechanism responsible for this behavior.
Solvation and rotational relaxation of coumarin 153 and 4-aminophthalimide in a new hydrophobic ionic liquid: Role of N–H…F interaction on solvation dynamics by Sudhir Kumar Das; Moloy Sarkar (23-28).
Wavelength-dependent fluorescence decay behavior of coumarin 153 and 4-aminophthalimide have been investigated by studying the time dependent fluorescence Stokes shift in the ps-ns time scale in a new hydrophobic room-temperature ionic liquid, 1-(2-methoxyethyl)-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate. The average solvation times from 4-aminophthalimide is estimated to be six times larger than the ones estimated from coumarin 153. Hydrogen bonding interaction (N–H…F) is found to play a significant role towards the dynamics of solvation in this specialized medium.Display Omitted► Time-resolved fluorescence of coumarin 153 and 4-aminophthalimide have been studied. ► Hydrophobic room-temperature ionic liquid has been used for the study. ► Average solvation time is found to depend on the probe molecules. ► Solute–solvent specific interaction is found to play an important role.The solvent relaxation and rotational dynamics of coumarin 153 and 4-aminophthalimide have been investigated in a hydrophobic room-temperature ionic liquid, 1-(2-methoxyethyl)-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate. The dynamic fluorescence Stokes shift measurements suggest that the average solvation time is highly dependent on the probe molecules. The average solvation time of 4-aminophthalimide is estimated to be six times larger than that of coumarin 153. Rotational coupling constant value of 4-aminophthalimide is also found to be larger than that of coumarin 153. Hydrogen bonding interaction between the probe molecule (4-aminophthalimide) and the ionic liquid is found to play a role on the dynamics of solvation in the present medium.
Narrow in-gap states in doped Al 2 O 3 by Montserrat Casas-Cabanas; Marion Frésard; Ulrike Lüders; Raymond Frésard; Cosima Schuster; Udo Schwingenschlögl (29-31).
Display Omitted► V, Cr, and Mn doping of sapphire is found to be substitutional. ► Transition metal d states are located in the fundamental band gap. ► Sizeable transmittance in the visible range is maintained.Based on XRD data testifying that the M ions occupy substitutional sites, transmittance measurement are discussed in comparison to electronic structure calculations for M-doped Al 2 O 3 with M = V, Mn, and Cr. The M 3d states are found approximatively 2 eV above the top of the host valence band. The fundamental band gap of Al 2 O 3 is further reduced in the V and Mn cases due to a splitting of the narrow band at the Fermi energy. Nevertheless the measured transmittance in the visible range remains high in all three cases.
Molecular dynamics study of the effect of pressure on the terahertz-region infrared spectrum of crystalline pentaerythritol tetranitrate by Andrey Pereverzev; Thomas D. Sewell (32-36).
Display Omitted► THz IR absorption spectra of PETN crystal were calculated using two MD methods. ► Spectra were calculated at T = 298 K for pressures P = 0, 1, 2, and 3 GPa. ► The two approaches yield similar predictions for the spectra. ► The terahertz spectra exhibit an overall blue shift with increasing pressure. ► Pressure-dependent Raman spectra at higher frequencies provide indirect validation.Terahertz infrared absorption spectra of crystalline pentaerythritol tetranitrate were obtained using classical molecular dynamics simulations for temperature T = 298 K and hydrostatic pressures P = 0, 1, 2, and 3 GPa. Two approaches were used to calculate the spectra; one based on combined normal-mode analysis and mode-relaxation calculations and the other on Fourier analysis of the dipole–dipole time autocorrelation function. The two methods yield similar, though not identical, positions and relative spectral amplitudes for all pressures studied. The predicted spectra exhibit an overall blue shift with increasing pressure, accompanied by a decrease in the integral absorption.
Thermodynamic excesses and the diffusion-controlled relaxation in the liquid system propan-2-ol–cyclohexane by Marta Łężniak; Krzysztof Bebek; Marzena Dzida; Wojciech Marczak (37-41).
Display Omitted► Positive excesses of volume and expansion of propan-2-ol + cyclohexane due to steric mismatch of the molecules. ► Positive excess enthalpy due to breaking of the H-bonds. ► Movements of propan-2-ol molecules hampered in dilute solutions. ► Long relaxation times in the mixtures containing ca. 1.5 mol% of propan-2-ol.Clusters of propan-2-ol molecules existing in the liquid phase due to hydrogen bonds disintegrate on dilution with cyclohexane. That leads to positive excesses of volume, expansion, compression and enthalpy. ‘Chemical’ and ‘physical’ contributions to the excesses were found by fitting the modified ERAS model to experimental data. The excess volumes and expansions proved to be mainly due to steric mismatch of the two types of molecules. For the same reason, movements of propan-2-ol molecules in dilute solutions are hampered, that is manifested in the ultrasonic relaxation times of nanoseconds order of magnitude.
Photoinduced intramolecular charge transfer process of betaine pyridinium: A theoretical spectroscopic study by Aurélie Perrier; Stéphane Aloïse; Zuzanna Pawlowska; Michel Sliwa; François Maurel; Jiro Abe (42-48).
Display Omitted► TD-DFT is used to investigate the spectral properties of a pyridinium betaine. ► Very good agreement with experiment is reached for absorption and emission. ► S2 state is involved in the absorption band and S1 in the emission band. ► Solvatochromic effects are reproduced. ► Charge distribution and dipole moment evolutions upon photoexcitation are analyzed.Using Time-Dependent Density Functional Theory and taking into account bulk solvent effects, we investigate the absorption and emission spectra of a betaine pyridinium molecule, the 2-(1-pyridinio) benzimidazolate (SBPa). This molecule exhibits strong photoinduced intramolecular charge transfer (ICT). We have identified two different electronic states involved, respectively, in the strong bathochromic ICT absorption band (S2) and in the moderate emission band (S1). The ICT process is analyzed in terms of charge distribution and dipole moment evolutions upon photoexcitation. These results are compared with steady-state spectroscopic measurements.
Influence of the exchangeable cation on the adsorption of 2-nitro-1-propanol on smectite surface models by D. Muñoz-Santiburcio; J. Ortega-Castro; F.J. Huertas; A. Hernández-Laguna (49-55).
Display Omitted► Exchangeable cation influence on 2-nitro-1-propanol adsorption on smectite surface. ► DFT(B3LYP)/6-31+G∗∗ calculations and AIM analysis are performed. ► Adsorption is favored by the cation in the order K > Na > Li. ► Adsorption is not favored in absence of cation. ► Adsorption weakens the interactions cation–surface.B3LYP/6-31+G∗∗ calculations and AIM analysis have been performed for studying the 2-nitro-1-propanol (NP) adsorption on smectite cluster models, employing Li+, Na+ and K+ as surface cations, and a fourth model with no cation. The adsorption is energetically more favored in the order K+>Na+>Li+. Adsorption takes place mainly by NP-NO2…cation and NP-OH…O interactions. The adsorption process weakens the interactions cation–surface, especially the interaction between the cation and the hydroxyl group in the ditrigonal cavity, which is believed to be particularly responsible for the differences observed in the adsorption energy among the different models.
Inhomogeneous broadening of electronic spectra at liquid interfaces by Ilan Benjamin (56-61).
Display Omitted► Interface electronic spectra broader than bulk spectra, in agreement with experiments. ► Surface region more heterogeneous than bulk on the scale of a single solvation shell. ► Spectral shift across the interface region contribute to observed spectral broadening.Molecular dynamics simulations of the electronic spectrum of a chromophore at the liquid/vapor interface of a non-polar solvent are used to investigate the factors that contribute to the spectral linewidth in the limit of inhomogeneous broadening. The interface spectra are broader than in the bulk due to an increase in heterogeneity on the scale of a single solvation shell and, to a greater degree, due to the spectral shift across the entire interface region. Insight into the broadening mechanism is obtained by considering the temperature effect and by calculating the spectra in layers defined both relative to the simulation box and relative to the intrinsic interface.
Study of intermediate states in shape transition of ZnO nanostructures from nanoparticles to nanorods by Bhupendra K. Sharma; Neeraj Khare; Mahesh Kumar; Praveen Kumar (62-67).
Display Omitted► Shape transition in ZnO nanostructures by varying the growth temperatures. ► Study of strain, defects and EF-VBM in shape transition of ZnO nanostructures. ► Strain and defects increases due to the formation of interface between two attached nanoparticles.ZnO nanostructures synthesized by chemical solution method were observed to exhibit a shape transition from nanoparticle to nanorod when the growth temperature was varied from 130 to 200 °C. At the intermediate growth temperatures (150–170 °C), nanoparticles start getting attached to form nanorods and exhibit enhanced strain and defects which seems to be due to the presence of interface between attached nanoparticles at these growth temperatures. The difference between valence band maxima and Fermi energy level at intermediate growth temperatures get increases which has been attributed to the enhancement of defects.
Radial growth of slanting-columnar nanocrystalline Si on Si nanowires by Su Kong Chong; Boon Tong Goh; Zarina Aspanut; Muhamad Rasat Muhamad; Chang Fu Dee; Saadah Abdul Rahman (68-71).
A proposed radial growth mechanism of slanting-nanocolumnar nanocrystalline Si structures on sidewall of the Si nanowires.Display Omitted► Radial growth of the slanted nc-Si columns on sidewalls of the Si nanowires. ► Tilt angles of the nc-Si columns are ranging from 38° to 70°. ► The estimated growth rate of the nc-Si columns is approximately 2 Å/s.The synthesis of Si nanowires was achieved via hot-wire chemical vapor deposition using an indium catalyst. In addition to the axial catalytic growth of Si nanowires, the radial growth of columnar structures occurred on the walls of the nanowires. The HRTEM results revealed that a mixture of amorphous Si and nanocrystalline Si grains was present within the columnar structure. The nanocrystalline Si nanocolumns were slanted at an angle of ∼66° towards the wall of the NWs. The amorphous Si background in the XRD pattern and asymmetric broadening in the Si peak of the Raman spectra provided evidence for the formation of nanocrystalline Si.
Trace elements distribution in Cu–Si alloys by Aleksandar M. Mitrašinović; Torstein A. Utigard (72-77).
Display Omitted► We developed a new method for metal refining where silicon was treated with copper as refining element. ► The highest concentration of trace elements was at the phase boundaries between Si and Cu–Si intermetallic. ► After treatment with Cu, 21 elements were not detected in pure Si. ► The amount of the trace elements decreased from 2 to 100 times in the refined Si compared to the initial metallurgical Si.The trace elements distribution in Cu–Si alloys is analyzed after mixing Si with Cu. The mass balance and atomic distribution showed that the highest concentration of trace elements was at the phase boundaries between Si and Cu–Si intermetallic. The concentrations of 21 trace elements in the refined Si were below detection limit of the ICP technique where 11 elements were below 1ppmat and another 7 elements were below 2ppmat. The amount of other elements decreased several times in the refined Si, compared to that in initial metallurgical grade silicon. The level of trace elements in refined Si allows utilization of the Si photo-catalytic characteristics for solar energy generation.
Static NLO responses of fluorinated polyacetylene chains evaluated with long-range corrected density functionals by Miroslav Medved’; Šimon Budzák; Tadeusz Pluta (78-84).
Display Omitted► We describe an alternative way of designing new high-grade NLO oligomeric materials. ► The asymmetry of a unit cell arises from a suitable substitution on a symmetric π-conjugated chain. ► A particular attention is paid to the performance of long-range corrected DFT methods. ► First hyperpolarizability of PFA eicosamer is more than 5× larger than the polymeric value of PMI.As an alternative to oligomeric systems with different skeleton atoms it is shown that asymmetry introduced by substitution on a symmetric π-conjugated chain can lead to molecular systems with high non-linear optical responses. First hyperpolarizability and related properties such as the bond-length alternation parameter, dipole moment and polarizability of polyfluoroacetylene (PFA) oligomers are investigated by the Hartree-Fock, DFT and MP2 approaches. Particular attention is paid to long-range corrected DFT methods (LR-DFT). Systematic behavior of the MP2/LR-DFT ratio enables to estimate Δβ L for the eicosamer to 76 × 103 a.u. what makes PFA oligomers attractive candidates for NLO applications.
Analysis of band gap formation in graphene by Si impurities: Local bonding interaction rules by Mary Clare Sison Escaño; Tien Quang Nguyen; Hideaki Kasai (85-90).
Display Omitted► Si clusters adsorption can lead to stable band gap opening in graphene. ► The band gap formation is solely due to the nature of Si–C local interaction. ► The distorted graphene retains the linear dispersion of π and π∗ bands at K points. ► Si structure rather than periodicity can induce electronic transition in graphene. ► Size of the gap changes with cluster size.We report band gap formation in graphene by using bonding interactions with Si impurities in the form of Si cluster (Si n ). We demonstrate that neither the distortion in graphene nor the periodicity of the adsorption can lead to band gap opening. The calculated band gap for Si2 is 0.83 eV at Dirac points and the effect of this Si–C interaction is maintained even when the cluster size is increased. However, there is a strong dependence of the size of the band gap on the size of the Si n . Analysis of the trend points to the change in the dispersion of the gap states due to the change in the Si–C bond.
Near-infrared photopolymerization: Initiation process assisted by self-quenching and triplet–triplet annihilation of excited cyanine dyes by Ihab Dika; Jean-Pierre Malval; Olivier Soppera; Véronique Bardinal; David Barat; Colette Turck; Arnaud Spangenberg; Aurélien Bruyant (91-95).
Display Omitted► The analysis of the dye photobleaching dynamics is achieved in situ into a droplet configuration. ► The photoinitiating properties of the dye stems from reactivity of its reduced and oxidized forms. ► In acrylate monomer, the reduced cyanine is responsible for the free radical photoinitiation. ► Addition of an amine accelerates the reaction due to the H-abstrator role the oxidized form. ► In this latter reactive pathway, the dye is ultimately regenerated.The mechanism of radical polymerization photoinitiated by a near-infrared absorbing indotricarbocyanine (HITC) was investigated using an indirect kinetics method based on the photobleaching dynamics of the dye. Despite similar photophysical features in glycerol and in pentaerythritol triacrylate monomer, HITC undergoes a very fast photobleaching in the acrylate resin which leads to photopolymerization at high power regime. The addition of an amine induces the decrease of photopolymerization threshold by a factor 5 with unexpected dye regeneration. These effects were correlated to the reactivity of the reduced and oxidized forms of HITC produced via triplet–triplet annihilation and ground state quenching processes.
Orbital interaction and local stability of Ni substituted Pd nanoalloys by Arunabhiram Chutia; Michio Tokuyama (96-101).
Display Omitted► Stability in Pd13− x Ni x (x = 1–13) nanoalloys. ► Subtle changes in stability at ∼70–80% Ni concentration. ► Ni (4s, 3p) and Pd (4s, 4p) orbital interactions are crucial. ► Pd 3d – Ni 4s orbital interactions are more favorable than Ni 3d – Pd 5s orbital.We investigated the relationship between orbital interactions and binding energy in Pd13− x Ni x (x = 1–13) nanoalloys. We employed, DFT at DNP/(PW91, BLYP, PBE and VWN-BP) level of functionals. In spite of higher cohesive energy of Ni as compared to Pd the thermodynamic stability of ∼70–80% Ni substituted Pd13 cluster is higher than Ni13. Orbital interactions are analyzed using partial density of states to elucidate the underlying reasons. In the overall stability of these clusters, the interaction between Ni (4s, 3p) and Pd (4s, 4p) orbitals are crucial for the explanation of subtle changes in their stabilities. This study provides a new orbital picture for thermodynamic stability in transition metal nanoalloys.
First Molecular Dynamics simulation insight into the mechanism of organics adsorption from aqueous solutions on microporous carbons by Artur P. Terzyk; Piotr A. Gauden; Wojciech Zieliński; Sylwester Furmaniak; Radosław P. Wesołowski; Kamil K. Klimek (102-108).
Display Omitted► Simulation results are in qualitative agreement with experiment. ► The balance occurs between porosity and carbon surface chemical composition in organics adsorption on carbons. ► Pore blocking determines adsorption properties of carbons.The results of 84 MD simulations showing the influence of porosity and carbon surface oxidation on adsorption of three organic compounds from aqueous solutions on carbons are reported. Based on a model of ‘soft’ activated carbon, three carbon structures with gradually changed microporosity were created. Next, different number of surface oxygen groups was introduced. We observe quantitative agreement between simulation and experiment i.e. the decrease in adsorption from benzene down to paracetamol. Simulation results clearly demonstrate that the balance between porosity and carbon surface chemical composition in organics adsorption on carbons, and the pore blocking determine adsorption properties of carbons.
Charge carrier kinetics in ZnO films and nanorods by D. Friedrich; L. Valldecabres; M. Kunst (109-115).
Display Omitted► Sensitization of ZnO films increases the decay rate of photogenerated charge carriers. ► The adsorption of dye molecules on ZnO nanorods does not increase the decay rate. ► The decay is mainly due to recombination by a multiexponential process.The kinetics of charge carriers in ZnO films and nanorods was analyzed by contactless transient photoconductance (TPC) measurements. The use of two excitation wavelengths allowed to identify the decay processes. The TPC signal displayed a significantly accelerated decay in ZnO films after sensitization with a ruthenium bipyridyl dye which was attributed to a higher electron–hole recombination whereas the electron–dye cation recombination was relatively slow. ZnO nanorods displayed no such destructive influence of the dye adsorption. Recombination processes took place over a large time range because of the heterogeneity of the samples.
Structure and bonding in polybromide anions Br−(Br2) n (n = 1–6) by Fabio Pichierri (116-121).
Display Omitted► DFT calculations are performed on Br−(Br2) n (n = 1–6) complexes. ► For n = 1, the symmetric Br 3 - anion is the local minimum. ► For n = 2–6, Br2 molecules bind to the central Br− anion to form stable complexes. ► QTAIM analyses reveal the presence of closed-shell interactions.The recent experimental characterization of a 3D polybromide network containing the octahedral complex anion Br−(Br2)6 by Feldmann’s group [Wolff et al., Angew. Chem., Int. Ed. 50 (2011) 4970] sparked our interest to investigate the structures and bonding in Br−(Br2) n complexes, n = 1–6, with the aid of quantum mechanical calculations. The quantum theory of atoms in molecules (QTAIM) indicates the presence of closed-shell interactions between dibromine molecules and the bromide anion.
Stabilization of tetragonal phase in ZrO2:Eu by rapid thermal heating by Ray Gunawidjaja; Thandar Myint; Hergen Eilers (122-126).
Display Omitted► Rapid thermal heating of nanophase ZrO2:Eu precursors is performed. ► Morphological and optical properties are measured. ► Analysis confirms that tetragonal phase is stabilized for temperatures up to 710 °C.Europium-doped Zr(OH)4 nanoparticles are heated via furnace and pyroprobe. As observed in X-ray diffraction and optical fluorescence spectroscopy, both heating techniques lead to mixed tetragonal and monoclinic crystalline ZrO2 phases. Three hours of heating in the furnace leads to 45% tetragonal phase at 400 °C and only 14% at 700 °C. Rapid 10 s heating in the pyroprobe, however, leads up to 68% tetragonal phase for temperatures between 570 and 710 °C. Incomplete dehydroxylation of the precursor may lead to the stabilization of the tetragonal phase.
Inclusion complexes of α-cyclodextrin and the cisplatin analogues oxaliplatin, carboplatin and nedaplatin: A theoretical approach by Cleber P.A. Anconi; Luciano da Silva Delgado; João B. Alves dos Reis; Wagner B. De Almeida; Luiz Antônio S. Costa; Hélio F. Dos Santos (127-131).
Display Omitted► We model three host–guest systems involving Pt(II) complex and α-CD. ► Structures and interaction energies are provided at two distinct DFT levels of theory. ► Increasing relationship between complex stability and intermolecular hydrogen-bond was found. ► Dispersion forces play a role for oxaliplatin inclusion compound ► Caboplatin forms quite stable complex with cyclodextrin.Quantum mechanics theoretical methodology has been applied in order to access and compare the relative stability of inclusion compounds formed by α-CD and the platinum (II) based drugs carboplatin, oxaliplatin and nedaplatin. The relative stability of the studied inclusion compounds has been discussed based on the number and type of hydrogen bonds identified between host and guest molecules. The evaluated energies at B3LYP/6-31G∗ level of theory strongly indicates that α-CD forms stable supramolecular systems with all studied cisplatin analogues, being the carboplatin@α-CD found as the most favorable inclusion complex among the platinum (II) derivatives studied in the present paper.
Structural characteristics, low threshold ultraviolet lasing and ultrafast carrier dynamics in high crystalline ZnO nanowire arrays by G.Z. Xing; D.D. Wang; B. Yao; A.Q. Lloyd Foong Nien; Y.S. Yan (132-136).
Undoped ZnO nanowire arrays are synthesized on sapphire substrates by a vapor transport growth. These nanowires exhibit ultraviolet lasing emission at room temperature with a remarkable low optical excitation threshold of ∼60 μJ/cm2. Systematic temperature-dependent and time-resolved photoluminescence studies suggest a direct near-band-edge radiative recombination with long lifetime of ∼1 ns from the ZnO nanowires. Such pure ZnO nanowires with unique optical properties are promising to find applications in multifunctional photonic nanodevices.Display Omitted► Well-aligned ZnO nanowire arrays. ► Ultraviolet lasing emission with low optical excitation threshold. ► UV recombination carrier dynamics investigation by temperature-dependent time-resolved photoluminescence spectroscopy. ► Direct near-band-edge radiative recombination with long lifetime of ∼1 ns.We report the structural characteristics and optical properties of well-aligned ZnO nanowire arrays. The quality of the produced nanowires is sufficiently good to act as efficient gain medium for stimulated emission. These nanowires exhibit ultraviolet lasing emission at room temperature with remarkably low optical excitation threshold of ∼60 μJ/cm2. Furthermore, recombination emissions involving carrier dynamics of pure ZnO nanowires were investigated by the temperature-dependent time-resolved photoluminescence spectroscopy. Direct near-band-edge radiative recombination with a long lifetime of ∼1 ns from the ZnO nanowires was observed. Such pure ZnO nanowires are promising for applications in multifunctional photonic nanodevices.
Selective control of vibrational modes with sequential femtosecond-scale laser pulses by Chen-Wei Jiang; Xiang Zhou; Rui-Hua Xie; Fu-Li Li; Roland E. Allen (137-140).
Display Omitted► Optimum FWHM laser pulse duration is 0.42 T for vibrational mode with period T. ► Much greater enhancement with optimized sequence of femtosecond-scale pulses. ► With enough optimized pulses, one can select various modes to be dominant. ► One can select modes useful in identifying or characterizing a chemical system.For nonresonant femtosecond-scale laser pulses, we showed earlier that the optimum FWHM pulse duration is 0.42 T if one wishes to achieve maximum relative excitation of a specific vibrational mode with period T. Here we show that much greater enhancement of a specific mode can be achieved with a sequence of laser pulses which have both this optimized duration and optimized delays between pulses. One can thus enhance a selected set of modes that are particularly useful in identifying or characterizing a chemical system, to lift them out of the background of less informative modes.
Assembly and electronic structure of octithiophene on Au(1 1 1) by Erwan Varene; Yan Pennec; Petra Tegeder (141-145).
Display Omitted► Octithiophene adsorbed on Au(1 1 1) forms well-ordered, closed packed films. ► Molecules adopt a tilted geometry with respect to the surface plane permitting intermolecular π–π-interaction. ► Energetic positions of unoccupied molecular states (LUMOs). ► Weak adsorbate/substrate-interaction.Scanning tunneling microscopy and spectroscopy as well as photoemission spectroscopy have been employed to study the adsorption behavior and electronic structure of α-octithiophene (8T) on Au(1 1 1). At a monolayer (ML) and bilayer coverage well-ordered molecular rows forming closely packed films are found, with 8T molecules tilted with respect to the surface plane allowing for intermolecular π–π-interactions. Two unoccupied electronic states are observed, which possess the same energetic position for 1 and 2 ML, indicating a low electronic coupling strength between 8T and the metallic substrate. This study shows that 8T grow on Au(1 1 1) in an ordered way generating a defined interface which is a basic requirement for future applications of 8T in (opto) electronic devices.
Energy level alignment in TiO2/dipole-molecule/P3HT interfaces by Erik M.J. Johansson; Rebecka Schölin; Hans Siegbahn; Anders Hagfeldt; Håkan Rensmo (146-150).
Display Omitted► Experimental results for polymer/molecular-dipole/TiO2 interfaces. ► Experimental quantification of the dipole induced change in the energy level alignment. ► High kinetic energy XPS was used to measure the fully assembled interfaces.Controlling the energy levels at the interface between an inorganic and an organic material is of importance to improve the properties in devices based on such hybrid interfaces, and can be obtained by the incorporation of dipole molecules between the materials. In this report interfaces containing TiO2, a dipole molecule (benzoic acid or 4-nitrobenzoic acid) and a polymer, poly(3-hexylthiophene) (P3HT) were investigated using high kinetic energy photoelectron spectroscopy. We could successfully measure through all materials in the fully assembled systems, and thereby experimentally quantify the dipole induced change in the energy level alignment of the polymer and the TiO2.
Workfunction variation across surface of an H-terminated diamond film measured using Kelvin probe force microscopy by J.H. Lay; K.M. O’Donnell; P.W. May (151-154).
Display Omitted► Kelvin probe force microscopy (KPM) performed on H-terminated diamond surface in ultra-high vacuum. ► Local variations in contact potential show work function variation up to 350 mV. ► Variations are observed even for structures of the same crystal orientation. ► The results show the Chemical vapour deposition (CVD) diamond work function is strongly affected by morphology.With the ability to image both topography and contact potential difference simultaneously, Kelvin probe force microscopy (KPM) is an effective tool for the electrical characterisation of diamond surfaces. In this work we measure variations in contact potential difference across the surfaces of boron-doped diamond films in order to investigate work function variations caused by surface features. Significantly, we demonstrate work function variations in excess of 300 mV across the surfaces of two differently prepared diamond films. Variations of this magnitude may have implications for the use of diamond in a number of electronic applications.
Ultrafast energy transfer in blended polyphenothiazine/polyphenylene vinylene film by Kang Meng; Qing Ding; Shufeng Wang; Qihuang Gong (155-158).
Display Omitted► Blended polymer film with polymer blend with complementary absorption spectra. ► Ultrafast Föster resonance energy transfer (FRET) process from PQ to MEH-PPV. ► The FRET process takes place as fast as 2 ps.Two-polymers, phenothiazine derivatives (PQ) and poly 2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene (MEH-PPV), who show complementary absorption to the solar spectrum are blended for broader absorption. The energy transfer from PQ to MEH-PPV is designed and observed at ultrafast time scale of ∼2 ps. Föster resonance energy transfer (FRET) process is regarded as the mechanism. Band gap of PQ is determined as 2.5 eV. With this design, a ladder type energy transfer and collection is suggested.
CO catalytic oxidation on iron-embedded hexagonal boron nitride sheet by Peng Zhao; Yan Su; Ying Zhang; Shu-Juan Li; Gang Chen (159-162).
We have investigated theoretically the catalytic oxidation of CO on Fe-embedded h-BN sheet. The reaction proceeds rapidly via the Eley–Rideal mechanism due to the low energy barriers.Display Omitted► CO catalytic oxidation on Fe-embedded h-BN sheet is studied for the first time. ► Fe can be constrained at a B-vacancy, and effectively activates the O2 molecule. ► The oxidation could proceed rapidly because of the low energy barriers.Using first-principles density functional theory, we have investigated the catalytic oxidation of CO on Fe-embedded hexagonal boron nitride (h-BN) sheet. Fe atom can be constrained at a boron vacancy site of h-BN sheet with a high diffusion barrier (3.70 eV), and effectively activate the adsorbed O2 molecule. The reactions between the adsorbed O2 with CO via both Langmuir–Hinshelwood and Eley–Rideal mechanisms were comparably studied. The reaction proceeds via the more favorable Eley–Rideal mechanism with a two-step route (CO + O2 → CO2 + O and CO + O → CO2). The energy barriers are 0.56 and 0.61 eV, respectively.
Wavelength-dependent photoproduct formation of phycocyanobilin in solution – Indications for competing reaction pathways by Benjamin Dietzek; Sonja Fey; Ricardo A. Matute; Leticia González; Michael Schmitt; Jürgen Popp; Arkady Yartsev; Gudrun Hermann (163-169).
Display Omitted► Novel insights into the photoreaction mechanism of phycocyanobilin. ► Photoproduct formation of PCB is pump-wavelength dependent. ► Alteration in protonation state is the rate limiting step in the reaction.Phycocyanobilin (PCB), an open-chain tetrapyrrole, makes up – slightly modified – the chromophore in phytochromes, the importance of which triggered model studies on the photochemistry of PCB in solution. We use pump-wavelength dependent femtosecond transient absorption spectroscopy including the near-IR region for probing to gain new insight into the photoreaction. The data reveal the coexistence of three ground state species: The dominant species PCBA undergoes photoreaction into PCBB and PCBC indicating a branching of the initial reaction path leading to formation of PCBB and PCBC. On this basis the photoreaction involves fast structural rearrangements within the tetrapyrrolic macrocycle, which are followed by slower rate-limiting changes in the protonation state of the pyrrolenine/pyrrole rings.
Polarizability-based equation of state: Application to CO, N2 and O2 by Sam P. de Visser (170-172).
Display Omitted► Polarizability-based equation of state connects pressure to polarizability, volume and temperature. ► Polarizability-based equation of state tested for small gas-phase diatomic molecules. ► Excellent agreement of calculated pV diagrams with the literature is found. ► Polarizability-based equation of state outperforms Ideal Gas Law. ► At low temperatures it is superior over the van der Waals equation of state.The description of dense gases and liquids still remains a challenge in thermodynamics. Recently, our group developed a new equation of state that is described by an attractive exponential contribution and a repulsive component that both are a function of polarizability volume and macroscopic volume. In this Letter, we apply this equation of state to moderately dense gases of CO, N2 and O2 over a broad temperature range. Literature data is excellently reproduced with the new equation of state and in comparison to the Ideal Gas Law or the original van der Waals equation of state gives substantial improvement.
Approximate spin-projected broken symmetry energies from optimized orbitals that are unrestricted in active pairs by Adrian M. Mak; Keith V. Lawler; Martin Head-Gordon (173-178).
Display Omitted► We derive and implement an orbital optimized approach to calculate the approximate spin-projected broken symmetry energy. ► Potential energy curves for homolytic dissociation of H2 are smooth and first derivative continuous. ► Static correlation energy recovered at extended H–H and N–N distances is comparable to the Yamaguchi APBS method.An orbital optimization approach to obtain molecular energies for biradicals and some classes of polyradicals based on Yamaguchi’s approximate spin projection broken symmetry (APBS) method is presented. The approximate spin-projected (AP) wave function is constructed using restricted open-shell orbitals for the high spin case, and spin polarization is carried out using the unrestriction in active pairs (UAP) procedure to obtain orbitals for the symmetry broken low spin case. The APBS-UAP method is applied to H2 and N2 as an illustration of spin polarizing one active electron pair, and three active electron pairs, respectively.
Development of isotropic site–site potential for exchange repulsion energy based on ab initio calculation. I. Closed shell system by D. Yokogawa (179-185).
Display Omitted► Isotropic site–site potential for exchange repulsion energy based on QM calculation. ► The potential can be applied to integral equation theories, such as RISM. ► Isotropic site–site potential for metal complex can be constructed.We developed isotropic site–site potential for exchange repulsion energy based on ab initio calculation. This work has two important points. One is that the introduced parameters can be determined from the electronic structure of a single molecule but not supermolecule. Another one is that we can employ the obtained potential directly in integral equation theory by using lookup-table approach. In this work, the present method was applied to simple examples (H2O, NH3, CH4, Cl−, and Na+) and metal complexes Zn(Me)2 and Zn(OH)2. The obtained potentials reasonably reproduced those obtained by Kitaura–Morokuma analysis and effective fragment potential.
Bond additive modeling 10. Upper and lower bounds of bond incident degree indices of catacondensed fluoranthenes by Damir Vukičević; Jelena Đurđević (186-189).
Display Omitted► Bond additive descriptors of flouorenthanes represented as face additive descriptors. ► Tight upper bound for each bond additive descriptor is given. ► Tight lower bound for each bond additive descriptor is given.Bond incident degree index is a descriptor that is calculated as the sum of the bond contributions such that each bond contribution depends solely on the degrees of its incident vertices (e.g. Randić index, Zagreb index, modified Zagreb index, variable Randić index, atom-bond connectivity index, augmented Zagreb index, sum-connectivity index, many Adriatic indices, and many variable Adriatic indices). In this Letter we find tight upper and lower bounds for bond incident degree index for catacondensed fluoranthenes with given number of hexagons.
Field enhanced photoemission: A new technique for the direct determination of the quasi-free electron energy in dense fluids by Yevgeniy Lushtak; C.M. Evans; G.L. Findley (190-193).
Display Omitted► Field enhanced photoemission (FEP) is presented as new technique to measure V 0 ( ρ ) . ► FEP is shown to yield accurate, high precision V 0 ( ρ ) for Ar. ► FEP is proposed as a technique for determining V 0 ( ρ ) in He.Previous experimental studies of the quasi-free electron energy V 0 ( ρ ) in dense fluids either directly measured V 0 ( ρ ) , using photoemission from an electrode immersed in the fluid, or extracted V 0 ( ρ ) from field ionization of a dopant dissolved in the fluid. In this letter, we present a new method to determine directly V 0 ( ρ ) , namely field enhanced photoemission. We show that this new method yields data comparable to those obtained from dopant field ionization, thereby making this method superior to direct photoemission studies. Moreover, unlike dopant field ionization, field enhanced photoemission is not limited by the solubility of a dopant in the fluid of interest.
Transient absorption spectroscopy detection of sensitized delayed fluorescence in chiral benzophenone/naphthalene systems by Paula Bonancía; M. Consuelo Jiménez; Miguel A. Miranda (194-196).
Benzophenone (BZP) sensitized, delayed naphthalene (NPT) emission is observed in laser flash photolysis as a negative band in the microsecond timescale. In the case of chiral BZP/NPT pairs, stereodifferentiation is observed in the kinetics of all photophysical processes.Display Omitted► Delayed naphthalene emission is observed by laser flash photolysis. ► It appears as a negative band in the microsecond timescale. ► Kinetic stereodifferentiation may be observed in all photophysical processes.Transient absorption spectroscopy has proven to be a powerful tool to investigate the formation and decay of excited singlet states upon triplet–triplet annihilation, following T–T energy transfer from a selectively excited sensitizer. Thus, upon selective excitation of benzophenone (BZP) by laser flash photolysis (LFP) at λ = 355 nm in the presence of naphthalene (NPT), a negative band centered at 340 nm has been detected, with growth and decay in the microsecond timescale. It has been assigned to the P-type NPT delayed-fluorescence. In the case of chiral BZP/NPT systems, stereodifferentiation has been observed in the kinetics of the involved photophysical processes.