Chemical Physics Letters (v.427, #1-3)
Editorial Board (CO2).
Ab initio prediction of the spectroscopic constants of NaN: Another potential candidate for a new Na-bearing interstellar molecule by Keisaku Ishii; Tetsuya Taketsugu; Koichi Yamashita (1-4).
This Letter describes ab initio prediction of the spectroscopic constants of NaN to aid experimental study and radio astronomical observations of this molecule.Potential energy curves for the lowest 3Σ−, 3Π, 1Δ, and 5Σ− states of NaN have been calculated by the multireference singles and doubles configuration interaction method, including Davidson’s correction for quadruple excitations (MR-SDCI(+Q)). It is shown that the former three are bound states, while the last one has no minimum. The ground state of NaN is predicted to be 3Σ− for which the binding energy is evaluated as 0.859 eV, and the rotational constants are calculated as B e = 11.632 and B 0 = 11.558 GHz. The spectroscopic constants presented here will help in the detection of NaN in interstellar space.
Spectra of the ν 1 and ν 3 bands of water molecules in helium droplets by Kirill E. Kuyanov; Mikhail N. Slipchenko; Andrey F. Vilesov (5-9).
Rotational–vibrational spectra of water molecules have been studied in helium droplets. The effective rotational constant (B He + C He)/2 was found to be close to that in free molecules. Fast rotational relaxation was ascribed to creation of short wavelength roton collective excitations in the He droplets.Depletion spectra of the ν 1 and ν 3 ro-vibrational bands of water molecules embedded in He droplets have been studied in the range of ν = 3600–3900 cm−1. The effective rotational constant of water in helium (B He + C He)/2 was found to be about 3% smaller than that of free H2O. Vibrational relaxation time of the ν 3 state in He was estimated from the laser power saturation dependence of the depletion signal to be about or longer than 7 × 10−9 s. Rotational relaxation time of different levels in the ν 1 and ν 3 states was estimated from the line widths to be about 2 × 10−12 s. Fast rotational relaxation was ascribed to the creation of short wavelength roton collective excitations in the He droplets.
Modeling diatomic potential energy curves through the generalized exponential function by C.S. Esteves; H.C.B. de Oliveira; L. Ribeiro; R. Gargano; K.C. Mundim (10-13).
In the present work, an alternative family of analytical potential energy curves (PECs) has been developed for stable diatomic molecular systems. These kinds of functions, that are based on q-exponential are used here to generalize the usual Bond-Order and Rydberg PECs.In the present work, an alternative family of analytical potential energy curves (PECs) has been developed for diatomic systems. These kinds of functions, that are based on q-exponential, are used here to generalize the usual Bond Order (BO) and Rydberg analytical PECs of diatomic molecular systems. The diatomic systems H 2 + and Li2 have been examined by means of this alternative approach. In particular, the computed vibrational spectra and spectroscopic constants were found to be in good agreement with the available experimental data.
Rovibrational energy levels for the electronic ground state of AlOH by Nicholas C. Handy; Stuart Carter; Yukio Yamaguchi; Se Li; Justin M. Turney; Henry F. Schaefer (14-17).
The vibrational–rotational energy levels of aluminum monohydroxide in its electronic ground state, X ∼ 1 A ′ AlOH, have been predicted using the variational method. The potential energy surface of the X ∼ 1 A ′ ground state of AlOH was determined employing the ab initio coupled cluster method with single, double, and perturbative triple excitations [CCSD(T)] and the correlation-consistent polarized valence quadruple zeta (cc-pVQZ) basis set. Low-lying J = 0 and J = 1 vibrational levels are reported. These are analyzed in terms of the quasilinearity of the molecule. Coriolis effects are shown to be significant. We hope that our predictions will be of value in the future when assigning rovibrational transitions in spectroscopic studies.The vibrational–rotational energy levels of aluminum monohydroxide in its electronic ground state, X ∼ 1 A ′ AlOH, have been predicted using the variational method. The potential energy surface of the X ∼ 1 A ′ ground state of AlOH was determined employing the ab initio coupled cluster method with single, double, and perturbative triple excitations [CCSD(T)] and the correlation-consistent polarized valence quadruple zeta (cc-pVQZ) basis set. Low-lying J = 0 and J = 1 vibrational levels are reported. These are analyzed in terms of the quasilinearity of the molecule. Coriolis effects are shown to be significant. We hope that our predictions will be of value in the future when assigning rovibrational transitions in spectroscopic studies.
Conformation and laser-induced fluorescence spectroscopy of phenetole in supersonic jet by V. Ramanathan; Prasenjit Pandey; Tapas Chakraborty (18-23).
Laser-induced fluorescence excitation spectrum for S1 ← S0 transitions of (a) phenetole and (b) anisole measured under the same expansion condition in a supersonic jet. The stick diagram representation of the FE spectrum of phenol (from Ref. [W. Roth, P. Imhof, M. Gerhards, S. Schumm, K. Kleinermanns, Chem. Phys. 252 (2000) 247.]) is presented here for a comparison.Laser-induced fluorescence excitation and dispersed fluorescence spectra of phenetole have been measured in a cold supersonic jet expansion. The spectral features reveal the presence of only one conformer of the molecule in the environment of the jet, and the finding is consistent with the quantum chemistry predicted relative stability and conformational isomerization barriers of different isomers. The vibronic bands in the dispersed fluorescence spectra have been assigned fully with the aid of the normal mode frequencies predicted by density functional theoretical calculation. The geometry in the S1 state has been optimized and the excited state vibrational frequencies have been calculated by CASSCF method. The theoretical results have been used to interpret the measured spectra.
Infrared photodissociation spectra and solvation structures of Cu+(H2O) n (n = 1–4) by Takuro Iino; Kazuhiko Ohashi; Yutaka Mune; Yoshiya Inokuchi; Ken Judai; Nobuyuki Nishi; Hiroshi Sekiya (24-28).
Coordination and solvation structures of Cu+(H2O) n with n = 1–4 are studied by infrared photodissociation spectroscopy and density functional theory calculations. The third H2O is found to hydrogen-bond to one of the first-shell waters in a (2 + 1) form rather than bind directly to Cu+ in a (3 + 0) form.Coordination and solvation structures of the Cu+(H2O) n ions with n = 1–4 are studied by infrared photodissociation spectroscopy and density functional theory calculations. Hydrogen-bonding between H2O molecules is detected in Cu+(H2O)3 and Cu+(H2O)4 through a characteristic change in the position and intensity of OH-stretching transitions. The third and fourth waters prefer hydrogen-bonding sites in the second solvation shell rather than direct coordination to Cu+. The infrared spectroscopy verifies that the gas-phase coordination number of Cu+ in Cu+(H2O) n is two and the resulting linearly coordinated structure acts as the core of further solvation processes.
Ab initio studies of hydrogen-bonded complexes: The H2O dimer, trimer and H2O―CO by Alessandra F.A. Vilela; Patrícia R.P. Barreto; Ricardo Gargano; Carlos R.M. Cunha (29-34).
The interaction energy of (H2O)2, (H2O)3 and H2O―CO complex calculated using ab initio methods combined with supermolecular approach are −4.88, −13.85 and −1.68 kcal/mol, respectively, while using the multipolar expansion method they are −4.667, −13.858 and −1.714 kcal/mol, respectively.In this work, we present the H2O interaction with H2O, (H2O)2 and CO molecules using ab initio calculation combined with both supermolecular and multipolar expansion methods. Molecular structures and electronic properties of monomers were calculated with MP2/6-311++G(3d,3p) level. The interaction energy for the H2O dimer, trimer and H2O⋯CO complex are −4.88, −13.85 and −1.68 kcal/mol, respectively, using the supermolecular approach and −4.667, −13.858 and −1.714 kcal/mol, respectively, using the multipolar expansion method, where the main contribution is the electrostatic one with 81.4%, 56.6% and 41.7% for the H2O dimer, trimer and H2O―CO, respectively, showing that these polar molecules interact mainly through electrostatic forces.
Theoretical study of the dark-oxidation reaction mechanisms for organic polymers by Guixiu Wang; Rongxiu Zhu; Dongju Zhang; Chengbu Liu (35-40).
Density functional theory calculations show the dark-oxidation reactions of organic compounds, including cumene, methyl 2-methylbutyrate, methyl methacrylate and methylacrylic acid, proceed via an α-H atom abstraction mechanism, which goes through the CCTC, H-abstraction transition state, and cage-like pair of radical in order, and finally the hydro-peroxide is formed.To model the dark-oxidation mechanism of organic polymers, the reactions of the corresponding model compounds, including cumene, methyl 2-methylbutyrate, methyl methacrylate and methylacrylic acid, with triplet O2 molecule, have been studied by performing density functional theory calculations at the UB3LYP/6-31G(d) level. The calculated results show that these model compounds can be oxygenated by O2 via an H-abstract mechanism. The structures of initial contact charge transfer complexes, transition states, intermediates of cage-like pairs of radicals, and final hydro-peroxides involved in the reactions have been shown in details. The present results are expected to provide a general guidance for understanding the dark-oxidation mechanism of organic polymers.
Atmospheric chemistry of C4F9O(CH2)3OC4F9 and CF3CFHCF2O(CH2)3OCF3CFHCF2: Lifetimes, degradation products, and environmental impact by A.M. Toft; M.D. Hurley; T.J. Wallington; M.P. Sulbaek Andersen; O.J. Nielsen (41-46).
FTIR smog chamber techniques were used to measure k(Cl + CF3CFHCF2O(CH2)3OCF2CFHCF3) = (2.97 ± 0.17) × 10−12, k(OH + CF3CFHCF2O(CH2)3OCF2CFHCF3) = (2.45 ± 0.14) × 10−13, k(Cl + C4F9O(CH2)3OC4F9) = (1.45 ± 0.16) × 10−12, and k(OH + C4F9O(CH2)3OC4F9) = (1.44 ± 0.10) × 10−13 cm3 molecule−1 s−1 in 700 Torr of air at 296 K. The atmospheric lifetimes of CF3CFHCF2O(CH2)3OCF2CFHCF3 and C4F9O(CH2)3OC4F9 with respect to reaction with OH radicals are estimated to be 46 and 83 days, respectively. In 700 Torr of N2/O2 diluent at 296 K, decomposition via C―C bond scission and reaction with O2 are competing loss mechanisms for the alkoxy radicals ROCH(O • )CH2CH2OR and ROCH2CH(O • )CH2OR (R = C4F9, CF3CFHCF2).FTIR smog chamber techniques were used to measure k(Cl + CF3CFHCF2O(CH2)3OCF2CFHCF3) = (2.97 ± 0.17) × 10−12, k(OH + CF3CFHCF2O(CH2)3OCF2CFHCF3) = (2.45 ± 0.14) × 10−13, k(Cl + C4F9O(CH2)3OC4F9) = (1.45 ± 0.16) × 10−12, and k(OH + C4F9O(CH2)3OC4F9) = (1.44 ± 0.10) × 10−13 cm3 molecule−1 s−1 in 700 Torr of air at 296 K. The atmospheric lifetimes of CF3CFHCF2O(CH2)3OCF2CFHCF3 and C4F9O(CH2)3OC4F9 with respect to reaction with OH radicals are estimated to be 46 and 83 days, respectively. In 700 Torr of N2/O2 diluent at 296 K, decomposition via C―C bond scission and reaction with O2 are competing loss mechanisms for the alkoxy radicals ROCH(O • )CH2CH2OR and ROCH2CH(O • )CH2OR (R = C4F9, CF3CFHCF2).
Photoelectron spectroscopy of titanium(IV) tert-butoxide by Igor Novak; Branka Kovač (47-50).
The electronic structure of titanium(IV) tert-butoxide Ti(OC(CH3)3)4 has been investigated by UV photoelectron spectroscopy and DFT calculations. We discuss the nature of metal–ligand bonding on the basis of empirical arguments.The electronic structure of titanium(IV) tert-butoxide Ti(OC(CH3)3)4 has been investigated by UV photoelectron spectroscopy (UPS) and DFT/OVGF calculations. This is the first reported UPS spectrum of a titanium alkoxide. We discuss the nature of metal–ligand bonding on the basis of empirical arguments.
Cooperativity halogen bonding effect – Ab initio calculations on H2CO⋯(ClF) n complexes by Sławomir J. Grabowski; Elżbieta Bilewicz (51-55).
The MP2/6-311++G(d,p) calculations on H2CO⋯(ClF) n complexes have been performed and the halogen bonding cooperative effect has been analyzed. The ‘atoms in molecules’ (AIM) theory was also applied to study halogen bonding interaction. For the systems analyzed, the strength of Cl⋯O interaction increases if the number of ClF molecules increases.The MP2/6-311++G(d,p) calculations on H2CO⋯(ClF) n complexes (n up to 6) have been performed and the halogen bonding cooperative effect has been analyzed. The ‘atoms in molecules’ (AIM) theory was applied to study halogen bonding interaction. For the systems analyzed, the strength of Cl⋯O interaction increases if the number of ClF molecules increases. For this interaction, oxygen acts as the Lewis base while Cl atom as the Lewis acid, that may be explained as an effect of the anisotropy of the electron charge distribution for chlorine atom.
Photoelectron spectroscopy of acetone cluster anions, [ ( CH 3 ) 2 CO ] n - ( n = 2 , 5 – 15 ) by Ryuzo Nakanishi; Azusa Muraoka; Takashi Nagata (56-61).
Geometrical structures and electronic properties of acetone cluster anions, [ ( CH 3 ) 2 CO ] n - ( n = 2 , 5 – 15 ) , are probed by photoelectron imaging spectroscopy combined with ab initio calculations. The dimer anion exhibits a distinctive stability due to the formation of a specific anion structure with twin pyramidally-deformed monomers.Photoelectron images of [ ( CH 3 ) 2 CO ] n - ( n = 2 , 5 – 15 ) were recorded at 3.49 eV. Analysis of the images provided the vertical detachment energies (VDEs) and photoelectron angular distributions (PADs) of [ ( CH 3 ) 2 CO ] n - . The n-dependence of these quantities starts with VDE = 0.83 ± 0.03 eV and β ≈ −0.3 at n = 2, and it ends up with 2.83 ± 0.03 eV and ≈0.1 at n = 15. These findings, in conjunction with ab initio results, indicate: (1) the formation of a specific anion structure at n = 2; and (2) the presence of a solvent-stabilized (CH3)2CO− valence anion in the larger analogues.
Thickness dependent photoconducting properties of ZnO films by S. Mridha; D. Basak (62-66).
Thickness dependent photoconducting properties of sol–gel ZnO films deposited on glass substrates have been investigated. Film with thickness below and around 260 nm shows the larger UV-to-visible rejection ratio, UV photoresponse magnitude and faster rate of photoresponse, which is correlated to the presence of optimum crystallite size and micropores in the film.The dependence of photoconducting properties on the thickness of ZnO films deposited on glass substrates by sol–gel spin coating technique has been investigated. The X-ray diffraction (XRD) results indicate that the film with thickness of 260 nm becomes maximum oriented along (0 0 2) direction. The field emission scanning electron micrograph (FESEM) shows that the grain size and volume of micropore increases with increase in thickness. Calculation shows that 260 nm film has the highest porosity. The photoconductivity studies exhibit maximum photoresponse for ultraviolet (UV) wavelength (<400 nm) for the film with 260 nm thickness which is correlated with the microstructural properties of the film.
Infrared spectrum and structure of the aci-nitro form of 2-nitrophenol in a low-temperature argon matrix by Maki Nagaya; Satoshi Kudoh; Munetaka Nakata (67-71).
2-Nitrophenol changes to the aci-nitro form by UV irradiation (λ = 248 nm). The structure is determined by a comparison of the observed infrared spectrum with the spectral patterns obtained at the DFT/B3LYP/6-31++G∗∗ level of calculation. A reverse isomerization occurs upon visible-light irradiation (λ > 450 nm).Matrix-isolation infrared spectroscopy was used to identify a reaction intermediate of 2-nitrophenol with an aid of density-functional-theory (DFT) calculations. The observed FTIR bands of a product from 2-nitrophenol upon irradiation of 248 nm were assigned to an aci-nitro isomer among 2 × 2 possible conformations, cis/trans around the C＝N+(O−)OH and CN+ (O−)―OH bond axes, by comparison with calculated spectral patterns. A reverse reaction from aci-nitro isomer to 2-nitrophenol was observed upon irradiation with λ > 450 nm. The mechanism of this reversible photoreaction is discussed in terms of the vertical transition wavelengths and the oscillator strengths obtained by time-dependent DFT calculation.
Surface alignment of the N-octadecylazatriquinacenium cation as determined by sum frequency generation on the surface of H2O and D2O by Steven Baldelli; Mark Mascal; Jordi Cerón Bertran (72-75).
Triquinacene is cyclic triene with the potential to photodimerize to the spherical hydrocarbon dodecahedrane. The orientation of a triquinacene-based amphiphile at the air–water interface has been studied by the surface sensitive vibrational sum frequency generation technique, which suggests that the dimerization of triquinacene may be possible in an aqueous monolayer.The dimerization of two triquinacene hemispheres to give dodecahedrane is the holy grail of cycloaddition chemistry. Despite the substantial effort which has been invested in achieving this reaction over the years, no cycloaddition product has been reported. The reason for this failure is that the required endo–endo reactive configuration, involving six double bonds in an S 6 symmetrical relationship, is difficult to achieve. In this preliminary report, the self-organization of a triquinacene-based amphiphile at the air–water interface is studied by the surface-sensitive vibrational sum frequency generation technique. The results indicate that the triquinacene bowl is directed into the aqueous subphase, which suggests dimerization of triquinacene may be possible in an aqueous monolayer.
Effect of hydroxylic compounds on the photophysical properties of ellipticine and its 6-methyl derivative: The origin of dual fluorescence by Zsombor Miskolczy; László Biczók; István Jablonkai (76-81).
The long-wavelength fluorescence of ellipticine (E) in methanol is assigned to photoinduced protonation by the solvent instead of a ‘quinoid-like’ tautomer formation via long distance, solvent-assisted excited-state intramolecular proton transfer, which has been proposed for olivacine, a compound differing from E only in the position of a methyl group.Photophysical parameters of ellipticine were compared to those of its 6-methyl derivative in various solvents. Since both compounds emitted dual fluorescence in methanol and ethylene glycol, the band peaking at low energy cannot be due to a tautomer formed via solvent-assisted excited-state proton transfer but originates from photoinduced protonation by the solvent. The mechanism and kinetics of the processes undergoing in the excited-state in the presence of OH− were revealed in methanol. Addition of OH− caused quenching for the excited ellipticine, whereas back-formation of the neutral excited compound proved to be the only important photochemical reaction of the protonated species.
Structure-making ions become structure breakers in glassy aqueous electrolyte solutions by H. Kanno; K. Yonehama; A. Somraj; Y. Yoshimura (82-86).
The average frequency of the uncoupled Raman OD stretching spectrum is always higher than that of glassy water for all the glassy aqueous electrolyte solutions investigated.Inorganic ions are usually classified as structure makers or structure breakers according to the viscosity B-coefficients of their aqueous solutions at ordinary temperature. Structure-making ions enhance the hydrogen bond strength while structure-breaking ones weaken the hydrogen bonds in aqueous solution. We here show that even structure-making ions (assigned by their viscosity B-coefficients at ordinary temperature) become a structure breaker in the sense that they weaken the hydrogen bonds in aqueous solution at low temperatures when we compare the strength of hydrogen bonds with that for glassy water.
Anomalous dynamic behavior of ions and water molecules in dilute aqueous solution of 1-butyl-3-methylimidazolium bromide studied by NMR by Masamichi Nakakoshi; Shinji Ishihara; Hiroaki Utsumi; Hiroko Seki; Yoshikata Koga; Keiko Nishikawa (87-90).
Dynamic properties of 1-butyl-3-methylimidazolium bromide ([bmim]Br) in D2O were investigated by NMR. The diffusion coefficients of [bmim]+and HDO were determined separately by the pulse field gradient method. The dynamics of Br− was estimated by the half-widths of the signals of 81Br-NMR. The results indicate that an anomalous dynamics, especially for [bmim]+, is evident in the region below ∼0.1 M. For [bmim]+ and HDO, maxima appeared in the curves of the diffusion coefficients plotted against the concentration. The relaxation time, T 2, for Br− showed a break in slope at this composition. Probable interpretations on these findings are presented.Dynamic properties of 1-butyl-3-methylimidazolium bromide ([bmim]Br) in D2O were investigated by NMR. The diffusion coefficients of [bmim]+and HDO were determined separately by the pulse field gradient method. The dynamics of Br− was estimated by the half-widths of the signals of 81Br-NMR. The results indicate that an anomalous dynamics, especially for [bmim]+, is evident in the region below ∼0.1 M (0.0019 in the mole fraction of [bmim]Br). For [bmim]+ and HDO, maxima appeared in the curves of the diffusion coefficients plotted against the concentration. The relaxation time, T 2, for Br− showed a break in slope at this composition. Probable interpretations on these findings are presented.
Surface projected electronic band structure and adsorbate charge transfer dynamics: Ar adsorbed on Cu(1 1 1) and Cu(1 0 0) by S. Vijayalakshmi; A. Föhlisch; F. Hennies; A. Pietzsch; M. Nagasono; W. Wurth; A.G. Borisov; J.P. Gauyacq (91-95).
On a timescale of only a few femtoseconds there is a decisive influence of the surface electronic structure on the charge transfer time between an excited adsorbate and a surface. This is of fundamental importance for any reaction mechanism at surfaces involving the transient formation of an excited electronic state.The influence of the surface projected electronic structure on resonant charge transfer is investigated on the Cu(1 1 1) and Cu(1 0 0) surfaces using core hole clock spectroscopy and wave packet propagation computations. The charge transfer time of core excited Ar ( 2 p 3 / 2 5 4 s 1 ) adsorbed in a dense Ar monolayer is 5.6 ± 0.1 fs and 3.5 ± 0.1 fs for the Cu(1 1 1) and Cu(1 0 0) surfaces. A two times longer residence time on Cu(1 1 1) than on Cu(1 0 0) is also obtained from theory and is attributed to the differences in the projected electronic band structure of the two metal surfaces, especially to the different energies of the surface projected band gap.
2D phase transition of PF6 adlayers at the electrified ionic liquid/Au(1 1 1) interface by Ge-Bo Pan; Werner Freyland (96-100).
2D phase transition of PF6 adlayers at the electrified ionic liquid/Au(1 1 1) interface has been investigated by in situ STM. At the potential above −0.2 V vs Pt reference, PF6 anions form Moiré-like patterns on Au(1 1 1). When the potential is changed towards more negative values, the structural changes occur gradually, and a (√3 × √3) phase forms at approximate −0.45 V.2D phase transition of PF6 adlayers at the electrified ionic liquid/Au(1 1 1) interface has been investigated by in situ STM. At the potential above −0.2 V vs Pt reference, PF6 anions form Moiré-like patterns on Au(1 1 1). When the potential is changed towards more negative values, the structural changes occur gradually, and a (√3 × √3) phase forms at approximate −0.45 V. More interestingly, the Moiré-like patterns are found to coexist with the uncompressed structures in most cases. The formation of the ordered adlayers can be attributed to the different solvation of PF6 in ionic liquid in comparison with aqueous solution.
Theory of nonlinear ac susceptibilities of dynamic electrorheological fluids under a dc electric field by W.J. Tian; J.P. Huang; K.W. Yu (101-106).
The real part of the third harmonic of local dipole moment P versus angular velocity ω 1 of suspended rotating particles for different volume fraction ρ.By using a perturbation approach, we theoretically investigate nonlinear ac susceptibilities of dynamic electrorheological fluids under a dc electric field. We consider the effect of a finite volume fraction. It is shown that the dynamic effect arising from a shear flow plays an important role in the ac responses. Meanwhile, the effect of a finite volume fraction offers a correction. The collective relaxation time is also derived by using our recently-established dielectric dispersion spectral representation, and it is shown to generally increase with the volume fraction of particles. Some theoretical results are compared favorably with the experimental observations by others.
A study of dielectrophoretically aligned gallium nitride nanowires in metal electrodes and their electrical properties by S.-Y. Lee; T.-H. Kim; D.-I. Suh; N.-K. Cho; H.-K. Seong; S.-W. Jung; H.-J. Choi; S.-K. Lee (107-112).
We quantitatively characterized the ac dielectrophoresis force on semiconducting gallium nitride (GaN) nanowires in suspension with variations of the ac electric field and frequency. The yield of aligned GaN nanowires increased with increasing ac electric field (up to 20 V p–p). The yield results indicate that the GaN nanowires were well aligned with a high yield of ∼80% over the entire array in a chip at the frequencies of 10 kHz and 20 MHz. In addition, the electrical properties of GaN nanowires prepared by dielectrophoresis were investigated using conventional three-probe schemes in field-effect transistor structures. (a) SEM image of GaN nanowires grown on substrate. (b) Enlarged image of (a). (c) A TEM image of the GaN nanowires. (d) PL spectrum from GaN nanowires measured at room temperature. (e) Image of the dielectrophoresis measurement set-up with (f) enlarged SEM image of the electrodes.We quantitatively characterized the ac dielectrophoresis force on semiconducting gallium nitride (GaN) nanowires in suspension with variations of the ac electric field and frequency. The yield of aligned GaN nanowires increased with increasing ac electric field (up to 20 V p–p). The yield results indicate that the GaN nanowires were well aligned with a high yield of ∼80% over the entire array in a chip at the frequencies of 10 kHz and 20 MHz. In addition, the electrical properties of GaN nanowires prepared by dielectrophoresis were investigated using conventional three-probe schemes in field-effect transistor structures.
Structural and electronic properties of CaSiO3 triclinic by J.M. Henriques; E.W.S. Caetano; V.N. Freire; J.A.P. da Costa; E.L. Albuquerque (113-116).
The CaSiO3 triclinic crystal was studied using a quantum mechanical first principles approach. Unit cell parameters have been optimized using the local density approximation (LDA) within the density functional theory (DFT) formalism. We also have calculated the electronic band structure, optical absorption, as well as effective masses for carriers.The CaSiO3 triclinic crystal was studied using a quantum mechanical first principles approach. Unit cell parameters have been optimized using the local density approximation (LDA) within the density functional theory (DFT) formalism in order to minimize the total energy. A comparison was made between these theoretical results and X-ray data. We also have calculated the electronic band structure, density of states, and optical absorption. Indirect band gaps E(Q → Γ) = 5.43 eV and E(B → Γ) = 5.44 eV, and a direct gap E(Γ → Γ) = 5.52 eV were obtained, as well as effective masses for electrons and holes at the maximum and minimum of valence and conduction bands, respectively.
D-band Raman intensity of graphitic materials as a function of laser energy and crystallite size by K. Sato; R. Saito; Y. Oyama; J. Jiang; L.G. Cançado; M.A. Pimenta; A. Jorio; Ge.G. Samsonidze; G. Dresselhaus; M.S. Dresselhaus (117-121).
We calculate defect-oriented Raman intensity (D-band) of nanographite as a function of crystallite size and excitation laser energy. The calculated results are compared with experimental results. This problem was an opened question for more than 20 years and this is the first answer.The Raman intensity of the disorder-induced D-band in graphitic materials is calculated as a function of the in-plane size of the graphite nanoparticles (L a) and as a function of the excitation laser energy. Matrix elements associated with the double resonance Raman processes, i.e., electron–photon, electron–phonon and electron–defect processes are calculated based on the tight binding method. The electron–defect interaction is calculated by considering the elastic scattering at the armchair edge of graphite, adopting a nanographite flake whose width is L a. We compare the calculated results with the experimental results obtained from the spectra for different laser lines and L a.
Comparison of the surface-enhanced Raman scattering on sharp and truncated silver nanocubes by Joseph M. McLellan; Andrew Siekkinen; Jingyi Chen; Younan Xia (122-126).
Sharp silver cubes (A) were truncated (B) by a solvent annealing process. The effects on the surface plasmon resonance bands (C) and on the surface-enhanced Raman scattering efficiencies using 1,4-benzendithiol as a probe molecule (D) are compared.Sharp and truncated Ag nanocubes ranging from 60 to 100 nm in size were synthesized, and the surface-enhanced Raman scattering (SERS) activities of these nanoparticles were compared with respect to both size and shape (i.e. sharp vs. truncated) using 514 or 785 nm lasers. Two trends were observed: (i) larger particles (90 and 100 nm) were found to have higher SERS efficiencies, and (ii) particles with shaper corners gave more intense SERS signals than their truncated counterparts. The difference in enhancement factor was mainly attributed to the variation in overlap between the laser source and surface plasmon resonance (SPR) bands as a function of size and degree of truncation.
Underwater laser ablation approach to fabricating monodisperse metallic nanoparticles by X.P. Zhu; Tsuneo Suzuki; Tadachika Nakayama; Hisayuki Suematsu; Weihua Jiang; Koichi Niihara (127-131).
Ag colloids abundant with fine particles around 4 nm was achieved by introducing a new experimental scheme of pulsed laser ablation of Ag plate in stirred water. Subsequent colloid aging led to significant narrowing of size distribution and refining of particle shape, attributed to a selective sedimentation of the suspensions.Pulsed laser ablation of Ag bulk in distilled water is investigated to synthesize metallic nanoparticles. Formation of Ag colloids abundant with fine particles no more than 4 nm has been achieved by introducing a new experimental scheme. Subsequent colloid aging led to significant narrowing of size distribution and refining of particle shape (from ellipsoidal or irregular to spherical). Morphology modification of the particles is attributed to a selective sedimentation of the suspensions during the aging. We demonstrate here a possibility of producing monodisperse metallic nanoparticles using the laser approach in a simple scheme.
K shell fluorescence yield of Cd and Zn in Cd1−x Zn x S thin films by E. Bacaksız; U. Cevik (132-136).
The K shell fluorescence yield ω K of Cd and Zn in Cd1−x Zn x S semiconductors was studied. Energy dispersive X-ray fluorescence technique was used to measure K X-ray photons. It was found that the K shell fluorescence yield ω K changed in Cd1−x Zn x S thin films for different compositions of x.The K shell fluorescence yield ω K of Cd and Zn in Cd1−x Zn x S semiconductors has been studied. Energy dispersive X-ray fluorescence (EDXRF) technique was used to measure K X-ray photons. Cd and Zn elements were excited by using 59.5 keV photons emitted by a 50 mCi 241Am radioactive source. The emitted characteristic K X-rays were detected by a Si (Li) detector having a resolution of 160 eV at 5.9 keV. It was found that the K shell fluorescence yield ω K changed in Cd1−x Zn x S thin films for different compositions of x.
Fabrication of well-ordered molecular device arrays by Lily Kim; Jurae Kim; Geun Hoi Gu; Jung Sang Suh (137-141).
We have developed a method for fabricating molecular device arrays using anodic aluminum oxide (AAO) templates and measured the I–V characteristics of the molecular device arrays fabricated on AAO templates.We have developed a method for fabricating molecular device arrays using anodic aluminum oxide (AAO) templates. Silver was electrochemically deposited in the pores of AAO templates, after which benzene-1,4-dithiol was self-assembled, and silver was then deposited again. This method is relatively simple, easily reproducible, and mass producible. The molecular devices are uniform in size and they are well-ordered in a hexagonal pattern. The density of the devices is very high (∼1.0 × 1010 devices/cm2). These well-ordered molecular devices could be used for fabricating nanoscale electronic devices.
A possible mechanism of uncatalyzed growth of carbon nanotubes by Y.W. Liu; L. Wang; H. Zhang (142-146).
The uncatalyzed edge growth of carbon nanotubes (CNTs) is investigated by first principles calculations and tight-binding molecular dynamic simulations. In this Letter, a growing mechanism for the uncatalyzed growth of CNTs, in which heptagons play a central role, is proposed.In this Letter, the uncatalyzed edge growth of carbon nanotubes (CNTs) is investigated by first principles calculations and using tight-binding molecular dynamics simulations. Both heptagon and pentagon have been found to be the stable defective configurations at the growing edge. However, the activation energy of pentagon formation is rather high in comparison with that of heptagon. The heptagons can be annealed out by reaction with adatoms transported to the tube edge. The edge of the open-ended NT may remain stable, if it is fed by a sufficiently large surface diffusion flux.
Signature of shape transition and shape coexistence in mesoscopic systems by Mihai Horoi; Koblar A. Jackson (147-152).
We investigate the phenomena of shape transition and shape coexistence in mesoscopic systems. We focus on the shape transition in silicon clusters, and Samarium isotope chain. In both cases we find that the shape transition region can be identified using the binding energy per particle.We investigate the phenomena of shape transition and shape coexistence in mesoscopic systems, specifically in atomic clusters and atomic nuclei. We focus particularly on the well-known shape transition in silicon clusters of n atoms, Si n , near n = 25, and the Samarium isotope chain near 152Sm. In both cases, we find that the shape transition region can be identified with a plateau in the curve of binding energy per particle vs. n −1/3, where n is the number of particles. To underscore the similarity of this signature of shape evolution for diverse systems, we show that it also applies to the growth of Lennard-Jones clusters.
Theoretical design of molecular photo- and acido-triggered non-linear optical switches by Fabien Mançois; Vincent Rodriguez; Jean-Luc Pozzo; Benoît Champagne; Frédéric Castet (153-158).
Photochromic/acidochromic equilibrium for dimethylaminophenylethylenyl-indolino[2,1-b]oxazolidine derivatives. The efficiency of the NLO switches is investigated as a function of chemical substituents R1–R4 by using various quantum chemical schemes.This theoretical Letter addresses the non-linear optical properties of a series of substituted dimethylaminophenylethylenyl-indolino[2,1-b]oxazolidine derivatives, which were recently shown to behave as multiaddressable NLO switches. The influence of the chemical nature of the substituent on the static and dynamic first hyperpolarizability, as well as of its grafting location, is investigated by using various semi-empirical and high level ab initio schemes. It is found that a para-substitution on the indolinic skeleton with a [(N,N-1,3-dimethylpyrimidine-2,4,6-trione)-5-yl]methylidenyl group should increase by 75% the efficiency of the switches.
Fragment molecular orbital calculations on large scale systems containing heavy metal atom by Takeshi Ishikawa; Yuji Mochizuki; Tatsuya Nakano; Shinji Amari; Hirotoshi Mori; Hiroaki Honda; Takatoshi Fujita; Hiroaki Tokiwa; Shigenori Tanaka; Yuto Komeiji; Kaori Fukuzawa; Kiyoshi Tanaka; Eisaku Miyoshi (159-165).
Graphic representation of cisplatin–DNA complex (taken from ‘1I1P’ dataset in Protein Data Bank) with explicit hydration by about a thousand water molecules. This system was calculated by the FMO–MP2 method with MCP-dzp basis set.We have realized a fully quantum mechanical treatment of large scale systems containing heavy metal atom, by introducing the model core potential (MCP) technique into the fragment molecular orbital (FMO) scheme. The scalar relativistic effects are incorporated by the use of MCP. This FMO/MCP method was applied to the divalent mercury ion hydrated with 256 water molecules at the second-order Møller–Plesset (MP2) perturbation level. The complex between cisplatin and DNA was also calculated with MP2, where about a thousand of water molecules and dozens of sodium ions were employed for the explicit treatment of hydration.
Theoretical simulation of the ROA spectra of neutral cysteine and serine by Magdalena Pecul (166-176).
Vibrational Raman Optical Activity spectra have been calculated for neutral conformations of amino acids cysteine and serine, in order to investigate the conformational dependence of the ROA differential intensity. The figure shows the ROA spectrum calculated for the most stable conformer of cysteine (on the right).Vibrational Raman Optical Activity (ROA) spectra have been calculated for neutral conformations of amino acids cysteine and serine. The purpose of the study was to investigate the conformational dependence of the ROA differential intensity, paying particular attention to the conformation of the polar side chains. In cysteine, the ROA intensities of side chain vibrations tend to vary fairly regularly with the value of the θ(NCCS) dihedral angle, while for serine the formation of hydrogen bonds by the side chain hydroxyl group seems to be the deciding factor determining the ROA intensities of the side chain vibrations.
Assessment of semiempirical methods for the computation of charge transfer in DNA π-stacks by Alexander A. Voityuk (177-180).
Using CAS-PT2 and CASSCF charge transfer energies and electronic couplings as reference data, we assess the performance of several semiempirical methods in the calculation of hole transfer in π-stacks of nucleobases. INDO/S is the most reliable of the methods examined. It provides very good estimates for the key CT parameters. While the MNDO, AM1 and PM3 methods give reasonable CT energies, they fail to provide acceptable values of the couplings matrix elements in the stacks.Using CAS-PT2 and CASSCF charge transfer (CT) energies and electronic couplings as reference data, we assess the performance of several semiempirical methods in the calculation of hole transfer in π-stacks of nucleobases. INDO/S is the most reliable of the methods examined. It provides very good estimates for the key CT parameters. While the MNDO, AM1 and PM3 methods give reasonable CT energies, they fail to provide acceptable values of the coupling matrix elements in the stacks.
The hydrogen bond strength: New proposals to evaluate the intermolecular interaction using DFT calculations and the AIM theory by B.G. Oliveira; F.S. Pereira; R.C.M.U. de Araújo; M.N. Ramos (181-184).
The B3LYP/6-311++G(d, p) calculations and the AIM topological parameters were applied to determinate the hydrogen strength of the H2O–H2O, H2O–HF, H2O–HCN, NH3–HF, HF–HF, NH3–HCN, H2O–NH3 and HCN–HCN hydrogen complexes.The optimized geometries of the H2O–H2O, H2O–HF, H2O–HCN, NH3–HF, HF–HF, NH3–HCN, H2O–NH3 and HCN–HCN hydrogen complexes were evaluated using B3LYP/6-311++G(d, p) calculations and parameters derived from Bader’s atoms in molecules theory. Moreover, in accordance with the relation existent between the hydrogen bond energy and the increments in the bond length of the proton donor species, we present new proposals to estimate the hydrogen bond strength through the atoms in molecules calculations, as well as using traditional parameters such as atomic charge transfer and the infrared bathochromic effect of the acid molecules.
Multicentered integrated QM:QM methods for weakly bound clusters: An efficient and accurate 2-body:many-body treatment of hydrogen bonding and van der Waals interactions by Gregory S. Tschumper (185-191).
The MC QM:QM method can accurately reproduce high-level energetics for a weakly bound cluster by essentially treating all 2-body interactions with a high-level QM method and the many-body interactions with a low-level QM method.An efficient integrated QM:QM technique for the description of weakly bound clusters is presented. The computational technique described here takes advantage of the recently developed multicentered (MC) integrated QM:QM methods and reliably describes hydrogen bonding and van der Waals interactions by treating all 2-body interactions with a high-level QM method and the many-body interactions with a low-level QM method. Even for small clusters of He, Ne, HF, and water, the MC QM:QM methods are typically 1–3 orders of magnitude faster than the high-level method while introducing an error of less than 1% in the interaction energy.
Carrier dynamics in porous silicon studied with a near-field heterodyne transient grating method by Masahiro Yamaguchi; Kenji Katayama; Qing Shen; Taro Toyoda; Tsuguo Sawada (192-196).
Near-field heterodyne transient grating method was applied for dynamics measurement of excited carriers in porous silicon, and the fundamental processes related to light emission are considered. The processes include trapping to surface states and two-body recombination of excited carriers, and the former process is the dominant source of light emission.The dynamics of excited carriers in porous silicon were investigated using the near-field heterodyne transient grating method, and the fundamental processes related to light emission were determined. The processes include trapping to surface states and two-body recombination of excited carriers, with trapping being the dominant source of light emission. Since nonlinear processes, namely two-body recombination, are included, it is necessary to measure the pump intensity dependence of the transient responses and to analyze them with a nonlinear differential equation in order to obtain accurate decay times.
The atomic and electronic structure of CdZnTe (1 1 1) A surface by Gangqiang Zha; Wanqi Jie; Tingting Tan; Peisen Li; Wenhua Zhang; Faqiang Xu (197-200).
From the low-energy electron diffraction (LEED) pattern for clean and smooth CZT (1 1 1) A surface, we can deduce that the original structure of CZT (1 1 1) A have been reconstructed to ( 1 1 1 ) - ( 3 × 3 ) R 30 ° . The reconstruction can be explained by vacancy model.The components of CdZnTe (1 1 1) A and B surface were measured by XPS. The result shows that Te atoms at the A topmost surface are chemically bonded by O atoms, but Te atoms are not at B surface. A new reconstruction structure ( 3 × 3 ) R 30 ° is uncovered for CZT (1 1 1) A surface through low-energy electron diffraction, and is explained in terms of a surface vacancy model. The surface state is measured by Angle-resolved photoemission spectroscopy, which confirms that there are dangling bonds at the reconstructed CZT (1 1 1) A surface.
Natural abundance 43Ca NMR study of calcium-containing organic solids: A model study for Ca-binding biomaterials by Alan Wong; Andrew P. Howes; Ray Dupree; Mark E. Smith (201-205).
Natural abundance 43Ca NMR data of calcium-containing organic solids is reported that act as models for calcium sites in biomolecules. The 43Ca NMR interaction parameters indicate small electric field gradients and chemical shift range. A correlation of the 43Ca isotropic chemical shift with Ca–O distance is found.As a first step for probing Ca sites in biomolecules using solid-state 43Ca NMR spectroscopy, natural abundance 43Ca NMR data of calcium-containing organic solids is reported. The 43Ca NMR interaction parameters indicate small electric field gradients and a relatively small chemical shift range for the calcium sites in these bio-related model compounds. A correlation of the 43Ca isotropic chemical shift with Ca–O distance is found: the 43Ca shift increases as the mean Ca–O distance decreases, with a strong deshielding being observed for calcium with strong Ca–O bonds (distance <2.4 Å) in both organic and inorganic materials.
Fluctuations of Raman spectra of hydrogenated amorphous carbon deposited on electrochemically-roughened silver by Andrzej Kudelski (206-209).
We showed that the process leading to the appearance of strong SERS fluctuations is practically insensitive to the structure of hydrogenated amorphous carbon clusters. Strong SERS fluctuations should be, therefore, explained by the temporal changes of the electromagnetic enhancement, rather than by the fluctuations of the resonance enhancement.Various deposits of hydrogenated amorphous carbon (a-C:H) on silver have been studied with surface-enhanced Raman scattering (SERS). When short accumulation time was used and scattered radiation were recorded with a Raman microscope, subsequently measured spectra of a-C:H often exhibited strong fluctuations. We showed by analysing the spectral fluctuations for various a-C:H samples, that the process leading to the appearance of strong SERS fluctuations is practically insensitive to the actual structure of a-C:H clusters. The appearance of strong SERS fluctuations should be, therefore, explained by the temporal changes of the electromagnetic enhancement, rather than by the fluctuations of the resonance enhancement.
Measurement of two-photon absorption coefficient of dye molecules doped in polymer thin films based on ultrafast laser ablation by Jung Rim Nam; Chang Ho Kim; Sae Chae Jeoung; Ki Soo Lim; Hwan Myung Kim; Seung-Joon Jeon; Bong Rae Cho (210-214).
Measurement of two-photon absorption coefficient of dye molecules based on fs-laser ablation threshold F th Two-photon absorption cross-section of a series of dyes (1a–3a) in polymer thin films was determined by measuring the femtosecond laser ablation threshold. The ablation threshold decreased gradually when the dopant increased. The two-photon absorption cross-section of the dye molecules dispersed in the polymer film was estimated by using the theoretical relationship between the ablation threshold of the blended polymeric thin films and the dye concentration. The relative values of two-photon absorption cross-section are in good agreement with those measured in solution. On the other hand, the absolute values are smaller than the latter.
H-bond patterns and structure distributions of water octamer (H2O)8 at finite temperatures by Toshiko Miyake; Misako Aida (215-220).
The configurational space of water octamer created by MC simulation is divided into the topology-distinct H-bond patterns. The relative molar Helmholtz energy for each H-bond pattern is evaluated. The thermodynamically favored structures of water octamer, which are energetically favored and readily feasible (entropy-favored for cluster formation), are presented.The NVT ensemble of water octamer is divided into the configurational subsets, which correspond to the topology-distinct H-bond patterns, and the relative molar Helmholtz energies of the H-bond patterns are evaluated. The method is based on the combination of standard Monte Carlo techniques with defined H-bond patterns. The structure distributions of water octamers at 200 and 300 K are presented based on the H-bond patterns instead of the ‘inherent structures’. The thermodynamically favored structures of water octamer, which are energetically favored and readily feasible (entropy-favored for cluster formation), are presented.
Geometric localisation in Möbius π systems by Patrick W. Fowler; Leonardus W. Jenneskens (221-224).
The apparent natural C2 symmetry of Möbius π systems is not a consequence of π distortivity.Evaluation of the eigenvalues of the bond–bond polarisability matrix for Möbius monocycles indicates that the apparent natural C2 symmetry of Möbius π systems is not a consequence of π distortivity but rather is due to the release of strain in the σ-skeleton.
An approximate second-order Møller–Plesset perturbation approach for large molecular calculations by Takahito Nakajima; Kimihiko Hirao (225-229).
CPU times (in S) with several MP2 approaches for glycine polypeptide.We propose an implementation of the large-scale MP2 approach obtained by combining the advantages of several approximate MP2 approaches. Our method is based on the local Laplace-transform MP2 method with the resolution of the identity approximation, which we denote the RILL-MP2 method. Applications of the RILL-MP2 method to linear glycine polypeptide and Se(CuPH3)2 molecules show that this approach is more efficient than the traditional or other approximate approaches without invoking loss of accuracy as the system size increases.
A novel parametrization scheme for classical and quantum mechanical simulations of large, floppy molecular systems by Andrea Miani; Paolo Carloni; Simone Raugei (230-235).
A novel set of coordinates and a new algorithm aimed at representing potential energy surfaces for floppy molecular systems from ab initio calculations are presented. Classical and Path Integral simulations on proton transfer in malonaldehyde and hydrogen bond in picolinic acid N-oxide establish the accuracy of the representation.We present an algorithm aimed at efficiently representing analytical full dimensional ab initio potential energy surfaces for floppy molecular systems. By introducing a new set of coordinates, we can define large amplitude displacements in one or more dimensions. Then, we use a general representation of the full dimensional potential energy surface based on a Taylor-like series expansion. Classical and quantum mechanical Path Integral Monte Carlo simulations on proton transfer in malonaldehyde and strong hydrogen bond in picolinic acid N-oxide establish the accuracy of our analytical representation and of our interpolating schemes.
Frozen core orbitals as an alternative to specific frontier bond potential in hybrid Quantum Mechanics/Molecular Mechanics methods by Arianna Fornili; Pierre-François Loos; Maurizio Sironi; Xavier Assfeld (236-240).
The use of Frozen Core Orbitals (FCOs) in addition to Strictly Localized Bond Orbitals (SLBOs) is proposed as an alternative solution to frontier bond length shortening in the LocalSCF(LSCF)/MM hybrid method. Calculations on model compounds illustrate that frontier bond length is correctly recovered without perturbing the description of the QM subsystem.The use of Frozen Core Orbitals (FCOs) at the frontier atom is proposed as an alternative to the specific frontier bond potential in the Local-SCF/MM method. The calculations illustrate that frontier bond length is correctly recovered without adding any specific force-field potential. It is shown that the same accuracy is reached for calculations using FCOs arising either from an atomic (ROHF) or from a molecular calculation using Extremely Localized Molecular Orbitals (ELMOs). In addition FCOs do not modify the description of the remaining of the QM subsystem from both an energetic and/or geometric point of view.