Chemical Physics Letters (v.355, #5-6)

Carbon nanotubes and nanowires grown from spherical carbon nano-particles by S. Botti; R. Ciardi; M.L. Terranova; S. Piccirillo; V. Sessa; M. Rossi (395-399).
In this Letter, we report a new method for the fabrication of carbon nanotubes (CNT) and nanowires where amorphous hydrogenated carbon nano-particles were used as precursor, without metal catalyst addition. In particular, depending on the process parameters, we obtained single walled nanotubes (SWNTs) with mean diameter 1.2 nm and carbon nanowires with mean diameter 250 nm. A discussion on the possible growth mechanism is also reported.

Excitation and dissipation of interacting many-electron system by Satoshi Yokojima; GuanHua Chen (400-404).
A new formalism based on the equation of motion for the reduced single-electron density matrix has been developed to simulate the dissipative interacting many-electron systems. The electron correlation is treated within the random phase approximation. The Markovian bath is adopted. The resulting nonradiative dissipative term is of Lindblad-like form. The formalism is applied to a butadiene molecule embedded in a liquid or solid environment, where the valence electrons are taken as the system and the nuclear vibrational modes as the bath. Various excitations are found decaying differently, e.g., different absorption peak widths are observed.

Humidity effects on the conductance of the assembly of DNA molecules by Dong Han Ha; Hyunsoo Nham; Kyung-Hwa Yoo; Hye-mi So; Hae-Yeon Lee; Tomoji Kawai (405-409).
We have studied the effects of relative humidity on the conductance of the assembly of poly(dG)–poly(dC) and poly(dA)–poly(dT) DNA molecules. The exponential dependence of conductance on the relative humidity is observed and explained in terms of ionic conduction through the hydration layers around DNA. The poly(dG)–poly(dC) specimen has larger sensitivity to the relative humidity and smaller activation energy for the ionic conduction than the poly(dA)–poly(dT) specimen. Our results show that the conductance of a specimen consisting of multiple DNA molecules might be strongly affected by the relative humidity.

The effects of two kinds of surface modifications (chemisorption and electrochemical modification) on the adsorption of methanol and atomic oxygen on Ag(1 1 0) surface have been investigated using B3-LYP method with cluster models. The promotion effect of halogen atoms was found to be mainly electrochemical. Both modifications, either by chemisorption of halogen atoms or by the presence of −q/+q point charges, increase the work function of the Ag(1 1 0) surface. Strong correlation between the adsorption energy of methanol, as well as atomic oxygen and the work function change induced by the two kinds of modifications has been found.

The electronic structure of the rutile(1 1 0) surface after formation of an isolated oxygen vacancy has been studied with density functional (DF) calculations and TiO2 embedded clusters. Restricted and unrestricted open shell wave functions have been analyzed in terms of atomic spin densities and Ti core level shifts. The removal of a neutral oxygen atom from the bridging oxygens of the TiO2(1 1 0) surface results in two unpaired electrons localized at the 3d orbitals of neighboring 5-coordinated Ti atoms. The electronic structure of an O vacancy on the surface of TiO2 is compared with that of the same defect in MgO and SiO2.

The lowest five singlet potential energy surfaces in the entrance region for the O(1 D) insertion into a C–C bond in cyclopropane have been calculated at the CASPT2/cc-pVDZ level of theory. It was found that the lowest surface is attractive, while the other four are repulsive. For comparison, the lowest five singlet potential surfaces for the O(1 D) insertion into the C–C bond in ethane were calculated using the same theoretical method. All the surfaces were found to be repulsive in the entrance region. The computational results are consistent with recent experimental observations for the O(1 D) reaction with small alkane molecules.

Synergistic effects of adsorption and interaction of DNA with mixed monolayers of anionic amphiphile and chromium(III) complexes by R. Vijayalakshmi; A. Dhathathreyan; V. Subramanian; Balachandran Unni Nair (431-437).
Investigations have been carried out to probe the interactions between double stranded DNA and non-amphiphilic chromium(III) complexes, [Cr(en)3]3+ and [Cr(phen)3]3+ (en-ethylenediamine, phen-1,10 phenanthroline) in mixed monolayers with dihexadecyl phosphate (DHP). Under the experimental conditions, the results show that there is a specific binding mode between [Cr(en)3]3+ and DNA at air/water interface based on adsorption followed by a strong binding of [Cr(en)3]3+ to DNA based on H-bonding. In case of [Cr(phen)3]3+, the results indicate that after initial adsorption of DNA to the metal complex, partial intercalation of Cr(phen)3 3+ takes place in the strands of DNA.

The intramolecular charge transfer (ICT) dual fluorescence of p-dimethylaminobenzamide (DMABA) in acetonitrile was found to show highly sensitive response to HSO4 over several other anions such as H2PO4 ,AcO and ClO4 . In the presence of bisulfate anion the dual fluorescence intensity ratio and the total intensity of DMABA decreased while the dual emission band positions remained unchanged. Absorption titration indicated that a 1:1 hydrogen bonding complex was formed between bisulfate anion and DMABA, which gave a binding constant of 2.02×104   mol −1   l that is two orders of magnitude higher than those for other anions. The obvious isotopic effect observed in the fluorescence quenching [K SV (HSO 4 )/K SV (  DSO 4 )=1.63] suggests that the hydrogen atom moving is an important reaction coordinate. It was assumed that the dual fluorescence response was due to proton coupled electron transfer mediated by hydrogen bonds within the 1:1 HSO4 -DMABA hydrogen-bonding complex.

Helical ice-sheets inside carbon nanotubes in the physiological condition by William H Noon; Kevin D Ausman; Richard E Smalley; Jianpeng Ma (445-448).
Molecular dynamics simulations were performed, in the physiological condition (300 K and 1 atm), on nanotube segments of various diameters submerged in water. The results show that water molecules can exist inside the nanotube segments, and, most importantly, the water molecules inside the tubes tend to organize themselves into a highly hydrogen-bonded network, i.e., solid-like wrapped-around ice sheets. The disorder-to-order transition of these ice-sheets can be achieved purely by tuning the size of the tubes. The results also suggest that the nanotubes have the potential to be used as proton-conducting pores for a variety of biological applications.

Wave packet dynamics on the repulsive potential surface of BaFCH3 excited at 745 nm by V. Stert; H.-H. Ritze; W. Radloff; K. Gasmi; A. Gonzalez-Ureña (449-456).
We studied the time evolution of the wave packet formed by the excitation of the Ba⋯FCH3 complex with a 120 fs laser pulse at 745 nm to its electronic A ̃ state which is repulsive at the ground state geometry and decays to Ba and CH3F fragments. By applying probe pulses with different wavelengths of 400 and 267 nm, respectively, we observed strongly different time dependences of the pump–probe signals for the BaF+ and Ba+ ions determined by the Franck–Condon windows available in both cases. The experimental results are qualitatively confirmed by theoretical studies based on ab initio calculations of the corresponding potential energy surfaces.

Correlations between singlet transition energies and energy gaps of corresponding pairs of occupied and unoccupied molecular orbitals were revealed in a series of benzodiazepines. The occupied orbital energies were taken from the photoelectron spectra of the compound investigated, the unoccupied ones were obtained from MNDO/d calculations, and the singlet energies were taken from the UV absorption spectra. The correspondence of the singlet transitions to certain molecular orbitals was established using MNDO/d calculations and comparing between UV and photoelectron spectra. It has been concluded that photoelectron spectroscopy can be applied for interpretation of UV absorption spectra of various compounds on the basis of similar correlations.

Dynamics of vibrational relaxation in the S1 state of carotenoids having 11 conjugated CC bonds by Helena Hörvin Billsten; Donatas Zigmantas; Villy Sundström; Tomáš Polı́vka (465-470).
Transient absorption spectra and kinetics in the 470–650 nm region were recorded for lycopene, β-carotene and zeaxanthin, all carotenoids with 11 conjugated double bonds, in two solvents with different polarity. Analysis of the red wing of the carotenoid S1–S n transition revealed presence of a pronounced shoulder at early delay times. The kinetics recorded at this low-energy shoulder of the S1–S n transition yields an additional decay component of 500–800 fs in addition to the main S1 decay. This dynamics is ascribed to a vibrational relaxation in the S1 state of the carotenoids.

Structure, ring currents and magnetic properties of 12b,12d,12f-triaza-12c,12e,12g-tribora-coronene by E. Steiner; P.W. Fowler; R.G. Viglione; R. Zanasi (471-477).
The title molecule (TTC), formally derived by replacing the inner C6 ring of coronene with (BN)3, is predicted at MP2/6-31G* and B3LYP/6-31G* levels to have a planar D3h equilibrium structure. Coupled Hartree–Fock calculations on TTC with the distributed-gauge continuous transformation of current density-diamagnetic zero (CTOCD-DZ) method predict a strongly diatropic coronene-like perimeter ring current, but with localized inner borazine-like diatropic circulations replacing the central paramagnetic circulation of coronene. On magnetic criteria, therefore, TTC is predicted to be at least as aromatic as coronene.

Does ozone have a barrier to dissociation and recombination? by R. Hernández-Lamoneda; Michael R. Salazar; R.T. Pack (478-482).
The barrier associated with the dissociation and recombination of ozone has been calculated using highly correlated ab initio methods. Our calculations show that, for fixed equilibrium values of the bending angle and one bond distance, there is a very small barrier, 100  cm −1 , as opposed to much larger values previously reported. When the saddle point geometry is optimized, the reaction path still contains a barrier but the top of the barrier lies below the dissociation limit.

We test the Maxwell–Stefan formulation for diffusion of multicomponent mixtures in zeolites and show that the mixture transport behaviour can be predicted on the basis of information of the pure component jump diffusivities at zero loading. The interaction between the diffusing, adsorbed, species is taken into account by introduction of interchange coefficients   D ij ; these encapsulate the correlations in the molecular jumps. A logarithmic-interpolation formula is suggested for estimating these interchange coefficients from information on the pure component jump diffusivities. To verify the developed Maxwell–Stefan formulation we use published molecular dynamics simulation results for transport diffusivities of CH4 and CF4 in Faujasite at 300 K. The predictions of the Maxwell–Stefan model are in very good agreement with the MD simulation results.

Analysis of nanometer inclusions in high pressure synthesized diamond single crystals by Long-Wei Yin; Mu-Sen Li; Zhi-Guang Gong; Bin Xu; Yun-Jing Song; Zhao-Yin Hao (490-496).
It was shown by transmission electron microscopy (TEM) that there contain nanoscale crystalline inclusions about several nanometers in dimension in diamond single crystals synthesized in the presence of Fe70Ni30 alloy catalyst under high pressure and high temperature (HPHT). The inclusions distribute homogeneously within the diamond matrix. It was indicated by selected area electron diffraction (SAD) patterns combined with EDS analyses that the inclusions consist of three main types: hexagonal graphite with a lattice constant of a=2.463  A ̊ , c=6.714  A ̊ , f.c.c. (FeNi)23C6 with a lattice constant of a=10.89  A ̊ , and f.c.c. γ-(FeNi) with a lattice constant of a=7.146  A ̊ .

Correlation between metal catalyst particle size and carbon nanotube growth by E.F. Kukovitsky; S.G. L'vov; N.A. Sainov; V.A. Shustov; L.A. Chernozatonskii (497-503).
The dependence of carbon nanotube diameters upon the size of nickel catalyst particles supported on amorphous carbon films was studied. Nanotubes were catalytically grown at different temperatures to elucidate the effect of temperature. The transformation of nanotube-growth mechanism takes place in the range 700–800 °C as evident from particle size–nanotube diameter relations, tip particles and nanotube morphologies. At low temperature (700 °C), the nanotube growth is conducted through solid tip catalyst particles. At 800 °C, nanotubes grow via liquid catalyst particles by extrusion mode. Low-temperature tube diameters reproduce essential features of original particle size distribution. In contrast, high-temperature tubes exhibit universal Gauss-like diameter distribution irrespective of catalyst particle sizes.

Photoconductivity of TiO2+Fullerene-C60 bilayers was studied. The fullerene layer conductivity increased significantly in presence of radiation with wavelengths below 300 nm incident onto TiO2. The sample response time was shorter than 20 ns.

Structures and stabilities of CaC3 isomers by A. Largo; P. Redondo; C. Barrientos; L.M. Ziurys (509-516).
A theoretical study of CaC3 species has been carried out. As a general trend, triplet states are found to be more stable than singlet ones for all isomers. The predicted global minimum is a rhomboidal species, 4t (3 B 1), whereas another rhomboidal four-membered ring, 3t (3 A 1), is predicted to lie quite close in energy (about 8.2 kcal/mol higher in energy at the G2(P) level). The corresponding singlet states, 3s (1 A 1) and 4s (1 A 1), lie about 11.5 and 13 kcal/mol, respectively, above the predicted global minimum. Therefore our calculations suggest that several species could be accessible to experimental detection.

The Method of Ideal Symmetry is applied to define new 3D and 4D molecular descriptors on the basis of some analogies with the vertex distance sum in molecular graphs. These new descriptors are employed together with well-known topological descriptors to make up a pool of available variables to perform a multilinear regression analysis of alkanes normal boiling points. Predictions are satisfactory and they compare fairly well with other available theoretical data. The fitting polynomials are improved through the analysis of nonlinear models and in such cases predictions are ameliorated, although not in a very spectacular manner. Finally, some possible extensions of the present study are pointed out.

Several properties were calculated within the AIM framework for diverse conformations of linear 1-alkanols on HF/6-31++G∗∗//6-31G∗ and B3LYP/6-31++G∗∗//B3LYP/6-31G∗∗ electron densities. The results revealed that δ-methylene groups are indistinguishable from those placed further away from the functional group for O–Cα–Cβ–Cγ gauche units, whereas they are specific when this unit is antiperiplanar. The internal rotation around the Cα–O bond only gives rise to noticeable modifications in the α and β-methylenes. The inclusion of electron correlation does not modify these trends, but the dependence displayed by the energy of nearly transferable fragments on the molecular size changes from destabilisation (HF) to stabilisation (B3LYP).

A sensitive detection technique for tunable diode laser spectroscopy is presented that is suited to study rotationally resolved spectra of weakly bound complexes. The method uses a low energetic plasma source to achieve an efficient concentration modulation in a supersonic planar jet expansion. The method is demonstrated with rotationally resolved spectra of the Π(110)←Σ(101) and Π(212)←Σ(101) internal rotation/vibration bands of ortho Ar–H2O in the ν 2 bend region of H2O. The latter transition has not been reported before and is recorded at 1658.0309(6) cm−1.

We report the first parametrization of a continuum model for the solvation of anions in DMSO solution. The present parameters used in conjunction with the PCM method predict the solvation free energy of 21 anions in DMSO solution with an average error of −1.2  kcal mol −1 , and a S.D. for the average error of only 2.2  kcal mol −1 . This low value of the S.D. shows that the present parametrization is capable of predicting accurate differences of the solvation free energies in DMSO solution and is reliable for modeling liquid phase chemical reactions.

Author Index (547-555).