Chemical Physics Letters (v.364, #5-6)

Optimized geometries and harmonic vibrational frequencies have been obtained for neutral and protonated acetic acid using quadratic configuration interaction methods. The proton affinity of acetic acid calculated at the QCISD(T)/6-311++G(3df,3pd)//QCISD/6-311+G(2d,2p) level of theory is 187.9±0.7  kcal mol −1 , in excellent agreement with the experimental value of 187.3 kcal mol−1. Thermochemical calculations using the CBS-Q, CBS-QB3, CBS-APNO, G2 and G2(MP2) model chemistries also display excellent agreement with the experimental proton affinity, suggesting that these model chemistries will provide accurate proton affinities for carboxylic acids that are too large to treat with high level ab initio methods.

Bipolar behavior revealed by D-π-D chromophores bearing dithienothiophene (DTT) as π-center in redox- and LE properties by Oh-Kil Kim; Han Young Woo; Jai-Kyoung Kim; William B. Heuer; Kwang-Sup Lee; Chung-Yup Kim (432-437).
A series of D/D- and D/A pair conjugated chromophores based on dithienothiophene, DTT, as conjugated linker (π-center) were synthesized (D-π-D and D-π-A) and studied optical and electrochemical properties. Unusual bipolar behavior was observed with D-π-D, displaying the redox property similar to that of D-π-A. Single-layer light-emitting (LE) devices fabricated with such electronically dissimilar oligomers exhibited a close resemblance in their diode characteristics that are commonly observed with bipolar LE materials.

Approach to estimate correlation energies of MNO3 (M=Li, Na, K) molecules by Shuping Zhuo; Jichong Wei; Guanzhi Ju (438-445).
According to the pair correlation energy results of MNO3 (M=Li, Na, K) at MP2-OPT2/6-311++G(d) level with Meld program and the transferability of pair correlation energies of M δ+ and NO3 δ in MNO3 molecules, a simple approach to estimate correlation energy of MNO3 is reported which can save a lot of computation time. The total correlation energy of MNO3 at MP2(full)/6-311++G(d) and MP2(full)/6-311++G(3df, 3pd) levels by Gaussian 94 procedure are also given in order to compare with those of Meld results and to discuss the influence of basis set size both on the calculation of correlation energy and on the presented simple approach.

Vibrational relaxation of ICN bulk and surface chloroform by John Vieceli; Ilya Chorny; Ilan Benjamin (446-453).
The vibrational relaxation of ICN at the surface of chloroform is studied using classical molecular dynamics computer simulations and is compared with the same process in the bulk liquid. Non-equilibrium classical trajectory calculations and equilibrium force correlation functions are used to investigate the factors that control the vibrational energy relaxation rate. We find that the relaxation rate depends on the initial excitation energy and is a factor of three slower at the interface than in the bulk. In addition, the frequency dependent friction at the interface is found to be orientation dependent, reflecting strong inhomogeneity.

Theoretical study of OH addition reaction to toluene by Inseon Suh; Dan Zhang; Renyi Zhang; Luisa T Molina; Mario J Molina (454-462).
Density functional theory (DFT) and ab initio multiconfigurational calculations have been performed to investigate the OH–toluene reaction. The applicability of DFT and ab initio theories to the OH–toluene reaction system is evaluated. The results reveal that the DFT method produces activation and reaction energies and rate constants of the OH–toluene reaction in good agreement with the experimental values. We predict the branching ratios of OH addition to ortho, para, meta, and ipso positions to be 0.52, 0.34, 0.11, and 0.03, respectively, significantly different from a recent theoretical study of the same reaction system.

The azimuthal angle of alternant hydrocarbons is considered and an upper bound has been obtained. Diastereotopic and enantiotopic isospectral isomers of the alternant hydrocarbons in context with the azimuthal angle are discussed.

The electronic structure of interfaces between aromatic adsorbates and metal oxide surfaces has been investigated using periodic hybrid ab initio Hartree–Fock-density functional theory calculations. Strong interfacial electronic coupling is observed for isonicotinic acid adsorbed on ZnO(1 0  1 ̄  0) and TiO2(1 1 0) surfaces. The results are in good agreement with experiments of ultrafast surface electron transfer processes for TiO2, and current experimental controversies regarding ZnO are clarified theoretically.

The magnetic exchange behaviour for μ-hydroxo and μ-acetato double-bridged chromium(III) dimer is investigated based on calculations of density functional theory combined with the broken-symmetry approach. It is demonstrated that there is a magnetic exchange cooperative effect of the two bridging ligands in a double-bridged dimer systems with approximate equal coupling intensity. Meanwhile, the calculated results reveal that the deprotonation of the μ-hydroxo ligand causes a sharp increase of the magnetic exchange interaction between the chromium centers. Replacing either the μ-hydroxo bridging ligand by one water bridging ligand or the μ-acetato bridging ligands by two terminal water ligands produces a relatively reasonable model to examine the contribution on the magnetic exchange interaction of another individual bridging ligand.

Quasi-aligned MoO3 nanotubes grown on Ta substrate by Yubao Li; Yoshio Bando (484-488).
Using infrared irradiation to heat a Mo foil in a moderate vacuum (5 Torr), quasi-aligned MoO3 nanotubes, about 5–8 μm long, were prepared on a Ta substrate. Most of the nanostructures show polygonal morphology with a hollow core in cross-sections. The width of nanotubes range from 50 to 300 nm, and the hollow core are about 20–150 nm in diameters. The nanotubes possess orthorhombic single-crystal structure and have preferentially grown along the [1 0 0] direction. Stacking faults normally form on the (0 2 0) planes, resulting from the layered structures.

Monte Carlo simulation with statistical perturbation theory is used to study the solvent effects on the relative free energies of solvation and the difference of partition coefficients (ΔlogP) for Cl to F mutation in diverse solvents. Comparison of relative free energies for mutation of Cl to F, in H2O (TIP3P) is made with the experimental work. There is a good agreement between two studies. There is also good agreement between the calculated structural properties of this study and the published and experimental results. For ion pairs, the solvent Born’s function and the differences in solvent–ion interaction dominate the differences in the relative free energies of solvation and the difference of partition coefficients.

The mixture of DMSO–water was studied with Car–Parrinello simulation techniques. A threefold coordination at the DMSO oxygen, methyl group hydrogen–oxygen atom contacts, Rüssel-structures and 1-DMSO–3-H2O clusters are observed. The H(DMSO)–O(H2O) and the H(DMSO)–H(H2O) radial distribution functions are almost identical. For different far water the angular distribution displays a dialectic character: close water orient with the oxygens to the methyl hydrogen far waters vice versa. The emerging picture for the dynamical behavior of the methyl groups is that of a near-hydrophilic–far-hydrophobic, where the hydrophobic character is probably dominant. A detailed mechanism of one such an event is given.

Ultrafast gain dynamics of the green fluorescent protein by P Didier; L Guidoni; G Schwalbach; M Bourotte; A Follenius-Wund; C Pigault; J.-Y Bigot (503-510).
We investigated the excited state dynamics of the uv mutant of the green fluorescent protein (GFPuv) using spectrally resolved femtosecond pump–probe spectroscopy. The gain dynamics of GFPuv is characterized by a ‘slow’ picosecond mono-exponential growth contrary to the wild type (GFPwt) where ultrafast components have been previously reported. As GFPwt and GFPuv share the same chromophore, this difference can be attributed to an intrinsic improved homogeneity of the GFPuv sample. The study of a synthetic GFP chromophore allows us to confirm the key-role played by the interactions chromophore–proteic cage in GFP photophysics.

The vibrational spectrum of the MnO2 and MnO4 anions in solid argon by Jian Dong; Yun Wang; Mingfei Zhou (511-516).
Laser-ablated manganese atoms react with oxygen in excess argon on condensation to form the neutral MnO and MnO2 oxide molecules as the major products. The MnO2 anions were produced via capture of ablated electrons by the neutral molecules. On annealing, the MnO4 anions were also formed and identified based on isotopic substitutions as well as density functional frequency calculations. Doping with CCl4 to serve as an electron trap gave the same neutral absorptions and virtually eliminated the anion absorptions, which strongly supports the anion identification.

Hydrogen ion diffusion in ruthenium oxide film is of significant interest because of its importance in capacitor, sensor and catalyst applications. In this study, a method based on potential–pH response measurement was used to determine hydrogen ion diffusion in ruthenium oxide films. The drift in the potential–pH response is believed to be due to the hydrated layer, which affects hydrogen ion diffusion onto the oxide film of the pH sensor. Hydrogen ion diffusion coefficient of ruthenium oxide films obtained from this method was 6×10−14   cm 2/s . The unique feature of the potential–pH response method is its relatively simple experimental procedure, which eliminates complications arising from surface related effects and/or presence of hydrogen traps in membrane such as those found in the conventional permeation method.

Recombination of D atoms resurfacing from the octahedral subsurface site on Ni(1 1 1) has been investigated as a model for the reaction of sub-surface D. The desorbing flux is made up of two components: translationally hot D2 formed in the reaction of energetic D atoms from the subsurface with chemisorbed D and a low energy component attributed to recombination of thermalised D. The D2 product shows no preferred scattering direction, consistent with a ‘hot precusor’ mechanism for reaction. Resurfacing D atoms scatter across the D/Ni(1 1 1) surface, losing any stereochemical memory of the resurfacing site before they react with chemisorbed D.

Density functional calculations are performed for bulk TiO2 rutile. The equilibrium geometry, bulk modulus and the Γ-point phonons are calculated. The local density approximation (LDA) and two generalized-gradient approximations (PBE and PW91) are used to describe the exchange–correlation energy. The LDA vibrational frequencies are in excellent agreement with experiment. PBE predicts the frequency of the transverse optic (TO) A 2u mode to be imaginary, leading to instability and to a ferroelectric phase transition. This result disagrees with all previous findings. The discrepancy between the PBE and LDA result is due to the larger equilibrium volume predicted by the PBE functional.

VUV photo-absorption cross-section for CCl2F2 by P. Limão Vieira; S. Eden; P.A. Kendall; N.J. Mason; S.V. Hoffmann (535-541).
The photo-absorption spectrum of CCl2F2 has been measured using synchrotron radiation in the range 5.5–11 eV (225>λ>110 nm). Electronic state assignments have been suggested for each of the observed absorption bands incorporating both valence and Rydberg transitions. The high resolution achieved has allowed vibrational series in one of these bands to be assigned for the first time. The measured VUV cross-sections may be used to derive the photolysis rate of CCl2F2 in the terrestrial atmosphere.

Single molecule spectroscopy of tetrahedral oligophenylenevinylene molecules by Melissa A. Summers; Matthew R. Robinson; Guillermo C. Bazan; Steven K. Buratto (542-549).
We probe the fluorescence from single molecules of a new class of tetrahedral oligo(phenylenevinylene) (OPV) molecules. Our results show that the tetrahedral molecules contain multiple chromophores with limited inter-arm coupling, but significant molecular motion about the central carbon results in fluctuations in the polarizability axis of the molecule. Loss in luminescence intensity is also observed during the fluctuations which is attributed to inter-arm coupling occurring when adjacent arms come close together. These fluctuations occur on the timescale of 100 ms to 10 s and are shown to be absent in the ‘arm’ molecules alone.

Solar induced fluorescence of gaseous yttrium monoxide by J.M Badie; B Granier (550-555).
We analyzed by optical spectroscopy the plume surrounding drops of yttrium oxide Y2O3 melted at the focus of a 2 kW parabolic solar furnace. The band spectra of YO molecule have been observed. These spectra result from a fluorescence phenomena excited by solar radiation. Their profiles evolution with the distance above the liquid sample reflects a dependence with the temperature. These spectra result from the emission of non-thermal equilibrium species, with vibrational temperatures from 2600 K down to 600 K. From our knowledge such low temperature YO spectra are reported for the first time.

Collective excitation dynamics and polaron formation in molecular aggregates by M Dahlbom; W Beenken; V Sundström; T Pullerits (556-561).
Real-space collective excitation dynamics in molecular aggregates is studied using a model where the electronic system is described via exciton theory with surface hopping. The nuclear dynamics are included using the Langevin equation where temperature and zero-point motions are entered via the fluctuation-dissipation theorem. Dynamic processes like exciton relaxation, localization, polaron formation and diffusion of self-trapped excitons, which commonly require different theories, are simultaneously described with our approach. Numerical simulations of small linear aggregates are performed. Contrary to the common view we show that exciton relaxation can temporarily increase exciton delocalization. The results are discussed based on the photosynthetic light-harvesting pigment-protein complexes.

Semiclassical dynamics based on quantum trajectories by Sophya Garashchuk; Vitaly A. Rassolov (562-567).
We present a trajectory-based method that incorporates quantum effects in the context of Hamiltonian dynamics. It is based on propagation of trajectories in the presence of quantum potential within the hydrodynamic formulation of the Schrödinger equation. The quantum potential is derived from the density approximated as a linear combination of gaussian functions. One-gaussian fit gives exact result for parabolic potentials, as do successful semiclassical methods. The limit of the large number of fitting gaussians and trajectories gives the full quantum–mechanical result. The method is systematically improvable from classical to fully quantum, as demonstrated on a transmission through the Eckart barrier.

The large-scale production of carbon nanotubes in a nano-agglomerate fluidized-bed reactor by Yao Wang; Fei Wei; Guohua Luo; Hao Yu; Guangsheng Gu (568-572).
Carbon nanotubes (CNTs) produced by catalytic chemical vapor deposition (CCVD) can be formed into loose agglomerates that can be fluidized during the growth process. This provides a way to prepare high-quality CNTs on a large scale at low cost in a nano-agglomerate fluidized-bed reactor (NAFBR). With the present fluidized-bed reactor design and catalyst preparation, 50 kg/day of carbon materials was synthesized, and a high yield of 70–80% CNTs was obtained. Fluidization characteristics distinctive to CNT growth in a fluidized-bed reactor are discussed.

Transient resonance Raman investigation of CHBr2 and CHBrCl radicals by Yun-Liang Li; Peng Zuo; David Lee Phillips (573-579).
Transient resonance Raman spectra of CHBr2 and CHBrCl radicals following ultraviolet photolysis of CHBr3 and CHBr2Cl, respectively, in methanol solution are reported. Most of the Raman intensity appears in the C–Br stretch and Br–C–Br bend or Cl–C–Br bend fundamentals accompanied by moderate intensity in their overtones and/or combination bands. The CH2Br radical was previously observed to have only one predominant Franck–Condon active mode (the C–Br stretch) with a strong overtone progression. The Franck–Condon region photodissociation dynamics of the CHBr2 and CHBrCl radicals appear to have more multidimensional character compared to halomethyl radicals like CH2Br.

Molecular dynamics simulation of Na+-DMP and Na+-MP2− ion pair in aqueous solution by Nam Sook Kang; Dong Hyun Jung; Kyung Tai No; Mu Shik Jhon (580-585).
Molecular dynamics simulations with an umbrella potential function in solution were carried out to obtain the potential of mean force for sodium-dimethyl phosphate (Na+-DMP) and sodium-methyl phosphate (Na+-MP2−). The Na+-DMP showed two minima in pmf profile, a less stable minimum of ca. 3.5 Å and a more stable minimum of ca. 5.0 Å, resulting in direct and indirect contact between two ions. On the other hand, the Na+-MP2− showed one prominent minimum in pmf profile, at approximately ca. 4.5 Å. Water molecules around Na+-DMP better formed a hydrogen-bonded network than around Na+-MP2−, showing a stronger interaction between water and the Na+-MP2−.

High-quality single-walled carbon nanotubes from arc-produced soot by Hisashi Kajiura; Shigemitsu Tsutsui; Houjin Huang; Yousuke Murakami (586-592).
High-quality single-walled carbon nanotubes (SWNTs) were obtained from arc-produced soot using a three-step purification process consisting of soft oxidation, air oxidation, and a high-temperature vacuum treatment. Firstly an oxide layer was formed on the surface of the metal catalyst, which prevents the SWNTs from undergoing metal-assisted dissociation during the process. After the final step, about 20% of the weight of the initial raw soot remained and the final product contained less than 1% metal. Scanning electron microscopy, transmission electron microscopy and Raman spectroscopy were used to characterize the SWNTs obtained.

The electrochemical halogenation of benzene: an in situ confocal microprobe Raman study by Guo-kun Liu; Bin Ren; Ren-ao Gu; Zhong-qun Tian (593-598).
The electrochemical substitution of benzene on Pt and Rh electrodes has been studied by a confocal microprobe Raman technique. The results showed that chlorination or bromination of benzene could occur with the positive-shift of the electrode potential. The two processes are significantly influenced by the roughness of the electrodes, the relative concentration of benzene and halide ion in solution and the entity of the substrates. The possible mechanism of the electrochemical halogenation of benzene has been proposed.

The OH radicals, generated by radiolysis, are found to react only in acidic conditions with halogenated benzenes by an electron transfer mechanism. The concentration of acid, at which solute radical cation of halogenated benzenes appear, is observed to depend strongly on the nature and number of halogen atoms in halogenated benzenes. A linear increase in the acid concentration required for solute radical cation formation is observed with electronegativity of halogen.

Synthesis of silicon carbide nano-junctions in a catalyst-assisted process by S.Z Deng; Z.S Wu; Jun Zhou; N.S Xu; Jian Chen; Jun Chen (608-611).
Nano-Y-junctions and nano-staggered-junctions that are formed by SiC nanorods were grown at elevated temperatures in a catalyst-assisted process. Transmission electron microscopy shows that the nanorods are typically around 20 nm in diameter and around 2  μ m in length. Nanorods with diameter down to below 2 nm may be observed from nano-junctions. High-resolution transmission electron microscopy shows that the nanorods are crystalline β-SiC.

A comparison is made between dipole moments calculated with and without the relaxation terms in the one-particle density matrix in excited state DFT calculations. It is concluded that there is a significant difference, and that results which do not include relaxation effects should not be used.

Doping-induced change of carrier mobilities in poly(3-hexylthiophene) films with different stacking structures by X Jiang; Y Harima; K Yamashita; Y Tada; J Ohshita; A Kunai (616-620).
Mobilities of positive charge carriers in poly(3-hexylthiophene) (PHT) films of 54%, 70%, 81%, and 97% in regioregularity were electrochemically measured over a range of doping levels. The results show that better ordered stacking structures enhance mobilities, but affect little features of the mobility change by doping. The common doping level of ca. 1% for the onset of the drastic mobility increase implies that the π–π stacking structures facilitating a charge transport in neutral or lightly doped PHT films are not responsible for the evolution of metallic conduction in PHT films.

We report for the first time a study of solvation characteristics of a solute in a completely miscible ternary solvent mixture by means of electronic absorption spectroscopy. The solvatochromic charge transfer band of two indicator dyes, viz, 2,6-diphenyl-4-(2,4,6-triphenyl pyridinium–1-yl) phenolate and N-ethyl-4-cyanopyridinium iodide has been studied in methanol + ethanol + acetone as a function of solvent composition at a fixed temperature. The transition energy in a ternary solvent mixture differs significantly from the average value of transition energy in component solvents weighted by the mole fraction of the solvents. To explain the results we have proposed a realistic model of solvation in a ternary solvent mixture. The excess or deficit of solvent composition in the immediate vicinity of solute over that in the bulk has been calculated.

Theoretical study of decomposition pathways for HArF and HKrF by Galina M Chaban; Jan Lundell; R Benny Gerber (628-633).
To provide theoretical insights into the stability and dynamics of the new rare gas compounds HArF and HKrF, reaction paths for decomposition processes HRgF→Rg+HF and HRgF→H+Rg+F (Rg=Ar, Kr) are calculated using ab initio electronic structure methods. The bending channels, HRgF→Rg+HF, are described by single-configurational MP2 and CCSD(T) electronic structure methods, while the linear decomposition paths, HRgF→H+Rg+F, require the use of multi-configurational wave functions that include dynamic correlation and are size extensive. HArF and HKrF molecules are found to be energetically stable with respect to atomic dissociation products (H + Rg + F) and separated by substantial energy barriers from Rg + HF products, which ensure their kinetic stability. The results are compatible with experimental data on these systems.

Motional broadening: an important distinction between multiple-quantum and satellite-transition MAS NMR of quadrupolar nuclei by Sharon E. Ashbrook; Sasa Antonijevic; Andrew J. Berry; Stephen Wimperis (634-642).
Multiple-quantum (MQ) and satellite-transition (ST) magic-angle spinning (MAS) are two very similar techniques used to obtain high-resolution or ‘isotropic’ NMR spectra of half-integer quadrupolar nuclei. In a variety of materials it is observed that some STMAS peaks are very broad compared with the corresponding MQMAS peaks, sometimes so broad that they are unobservable. We present 17O (I=5/2) NMR spectra of two materials, chondrodite (2Mg2SiO4· Mg(OH)2) and clinohumite (4Mg2SiO4·Mg(OH)2), exhibiting this phenomenon and show that the cause is motional broadening arising from the combined effects of molecular reorientation, the quadrupolar interaction and MAS.

Author Index (644-654).