Chemical Physics Letters (v.357, #3-4)

Energy minimizations using Hartree–Fock dispersion (HFD) model and exp-6-1 potentials predict very different global minima for anthracene trimer and naphthalene tetramer. Comparison of the predicted geometries with available experimental data demonstrates the clear superiority of the HFD model in structure prediction.

Local density augmentation from fluorescence lifetime for anthracene N,N-dimethylaniline exciplex in supercritical carbon dioxide by Takafumi Aizawa; Yutaka Ikushima; Norio Saitoh; Kunio Arai; Richard L. Smith (168-172).
Local density augmentation around exciplex between anthracene and N,N-dimethylaniline in supercritical carbon dioxide was measured by fluorescence lifetime at 40 °C and at pressures from 9.3 to 19.1 MPa. In the near-critical (9.3–10.5 MPa) region, the exciplex was more stable than that predicted by Kirkwood analysis, which means strong influence of local density augmentation around the exciplex.

Excited-state dynamics and photophysics of 2,2-furil by Ajay K. Singh; Dipak K. Palit (173-180).
Photophysical properties of the excited singlet and triplet states of 2,2-furil in different kinds of media have been characterized by steady-state emission as well as by laser flash photolysis techniques. Emission characteristics of furil is seen to be independent of the kind of solvent media, indicating the absence of any kind of conformational changes in the excited state. This fact has been corroborated by the results of transient absorption studies in ultrafast time domain.

Infrared matrix isolation spectra of SF6 dimers by T.D. Kolomiitsova; Z. Mielke; D.N. Shchepkin; K.G. Tokhadze (181-188).
The infrared spectra of 32 SF 6,  33 SF 6 and 34 SF 6 dimers were studied in argon and nitrogen matrices. The spectra of SF6 dimers of like and unlike isotopomers were also calculated taking into account the resonance dipole–dipole and dipole-induced dipole interactions between two triply degenerate oscillators. Two absorption bands with site structure are observed for (32 SF 6)2, (33 SF 6)2 and (34 SF 6)2 in argon; the ν X,Y band is blue shifted and the ν Z band is red shifted from the ν3   SF 6 band in accordance with calculated spectra. Three and two components of the predicted quadruplets are identified for 32 SF 6–34 SF 6,  32 SF 6–33 SF 6 , respectively. In the spectra of (SF6)2 in nitrogen matrices the splitting of ν X,Y component of the resonance doublet was observed.

Vapor–liquid equilibrium simulations of the SCPDP model of water by J.L. Rivera; M. Predota; A.A. Chialvo; P.T. Cummings (189-194).
Molecular simulations were carried out using the self-consistent point dipole polarizability model (SCPDP) of water in the region of vapor–liquid equilibrium. The methods of isothermal–isochoric molecular dynamics (NVT–MD) and Gibbs ensemble Monte Carlo (GEMC) were employed to calculate orthobaric densities and vapor pressures; NVT–MD also yields surface tensions and interface thickness. Agreement was found between the two methods, particularly at lower temperatures, but compared with experimental results, this model over-predicts vapor pressures and densities, and under-predicts the liquid density, surface tension, and interface thickness. The interface thickness predicted by the SCPDP model showed better agreement with experimental results than a simpler extended point charge model (SPC/E).

IR multiphoton depletion spectroscopy of metal cluster–ligand complexes by Benoit Simard; Stéphane Dénommée; David M. Rayner; Deniz van Heijnsbergen; Gerard Meijer; Gert von Helden (195-203).
Free electron laser IR photodepletion spectroscopy of metal cluster–ligand complexes in a molecular beam is demonstrated on Ag n (NH3) m complexes in the range 800–1150 cm−1. Where direct comparison can be made, our spectra agree with spectra measured by CO2 laser photodepletion spectroscopy. New vibrational spectroscopic data addressing previously unreachable spectral regions, including results for deuterated ND3 are reported for complexes of Ag3, Ag4 and Ag5.

Exclusive production of excited-state sulfur (1D) atoms from 193 nm photolysis of thietane by Fei Qi; Liusi Sheng; Musahid Ahmed; Darcy S. Peterka; Tomas Baer (204-208).
Tunable synchrotron radiation has been used to probe the dissociation dynamics of thietane (C3H6S) at 193 nm, providing selective determination of the translational energy distribution of both excited (1 D) and ground-state (3P) sulfur atoms, with momentum-matching to the C3H6 co-fragment. The results suggest that the sulfur atom is produced almost exclusively in its excited (1D) state, with ground-state (3P) production less than 5%. The first single-photon ionization efficiency (PIE) spectrum for the S(1D) state with a resolution of 0.2 eV is reported.

The CH3F⋯CH3F and CH3F⋯H2O complexes produced by supersonic-jet expansion have been deposited on a cold plate using a standard matrix-isolation technique. By comparing the infrared spectra measured with an FTIR spectrophotometer with the results of DFT calculations, the structure of CH3F⋯CH3F is estimated to be anti-parallel, while that of CH3F⋯H2O has a bent C–F⋯H–O intermolecular hydrogen bonding. The difference in the structure of CH3F dimer from that of CH3I dimer is explained in terms of the dipole–dipole interaction of two methyl halide molecules and the dispersion force of halogen atoms.

A microscopic theory of tracer diffusivity: crossover to the hydrodynamic limit by Sk. Musharaf Ali; Alok Samanta; Swapan K. Ghosh (217-222).
A microscopic approach is developed for the tracer diffusivity in fluids based on the concepts of mode coupling theory. The calculated numerical results for the tracer diffusivity in a Lennard-Jones (LJ) fluid are shown to be in good agreement with the corresponding simulation results. The hydrodynamic limit is found to be reached at higher mass and larger size of the solute particle which is consistent with the results of simulation studies.

Intermolecular interactions in aniline–benzene hetero-trimer and aniline homo-trimer ions by Kazuhiko Ohashi; Yoshiya Inokuchi; Nobuyuki Nishi; Hiroshi Sekiya (223-229).
The charge distribution and binding features of aniline–benzene hetero-trimer and aniline homo-trimer ions are investigated by vibrational spectroscopy and by near-infrared photodissociation and spontaneous unimolecular dissociation of mass-selected cluster ions. The absence of the charge resonance absorption indicates the charge localization in the trimer ions. Substantial red-shifts and enhanced intensities of the vibrational transitions suggest strong perturbations to the NH oscillators. The trimer ions are stabilized by the hydrogen-bonding interaction through the NH2 group of the charged aniline with the neutral molecules rather than the charge-delocalization interaction among the component molecules.

The restricted active space (RAS) state interaction approach with spin–orbit coupling by Per Åke Malmqvist; Björn O. Roos; Bernd Schimmelpfennig (230-240).
A method to compute spin–orbit coupling between electronic states is presented. An effective one-electron spin–orbit Hamiltonian is used, based on atomic mean field integrals. The basic electronic states are obtained using the restricted active space (RAS) SCF method. The Hamiltonian matrix is obtained by an extension of the restricted active space state interaction (RASSI) method. Several hundred states can be included. Tests for atoms and molecules from the entire periodic system show accurate results. Computed spin–orbit effects on relative energies are normally accurate within a few percent. The method has been included in the MOLCAS-5.0 quantum chemistry software.

Selective excitation in dipole coupled systems by Jamie D. Walls; Malgorzata Marjanska; Dimitris Sakellariou; Franca Castiglione; Alexander Pines (241-248).
In this Letter the possibility of selective excitation in coupled multispin systems is studied theoretically. A general method of transforming any selective pulse developed for uncoupled systems into a form that is selective in coupled systems is presented. This is accomplished by adding a small perturbation to a decoupling radiofrequency (RF) field. When viewed in an interaction frame given by the decoupling RF field, this method generates, in an averaged sense, a propagator similar to the propagator of uncoupled spins under a shaped RF pulse. Preliminary experimental results are presented for the case of selective excitation in proton nuclear magnetic resonance in liquid crystals.

Optical absorption of Ag oligomers dispersed within pores of mesoporous silica by Huijuan Bi; Weiping Cai; Huazhong Shi; Xiong Liu (249-254).
Small Ag particles were obtained by thermal decomposition of silver nitrate within pores of mesoporous silica in H2 at temperatures from 100 to 700 °C. For the sample treated at 100 °C, the absorption spectrum exhibits three absorption peaks including both surface plasmon resonance peaks at 400 nm from Ag nanoparticles and two new peaks located at 300 and 330 nm which are attributed to the Ag oligomers. Increasing the temperature, the absorption from oligomers become weakened and finally vanishes, whereas the absorption peak at 400 nm becomes gradually dominating. When exposing the fresh sample to air, an obvious depression following an enhancement in absorption is found, which is considered to result mainly from oxidation of Ag particles. The lifetime of these oligomers can reach as long as 4 days in air, which may be due to the formation of H-bonds and the slow diffusion of oxygen in the confined pores.

By replacing the distances between pairs of vertices with relative distances, we define a novel valence hyper-Wiener index (VWW). The valence hyper-Wiener index extends the usefulness of the hyper-Wiener index to unsaturated hydrocarbons.

The microscopic model used previously for interpreting the low-energy electro-absorption (EA) spectrum of the fullerene crystal is applied to reproduce theoretically the corresponding signal at 4.5 eV. It is demonstrated that the spectral feature observed at that energy, in spite of its shape resembling that located at 3.7 eV and attributed to CT excitons, is in fact due to a Frenkel state.

Lead adsorption on carbon nanotubes by Yan-Hui Li; Shuguang Wang; Jinquan Wei; Xianfeng Zhang; Cailu Xu; Zhaokun Luan; Dehai Wu; Bingqing Wei (263-266).
Carbon nanotubes (CTNs) show exceptional adsorption capability and high adsorption efficiency for lead removal from water. The adsorption is significantly influenced by the pH value of the solution and the nanotube surface status, which can be controlled by their treatment processing. The adsorption isotherms are well described by both Langmuir and Freundlich models. Our results suggest that CNTs can be good Pb2+ adsorbers and have great potential applications in environmental protection.

Forming multiwalled carbon nanotubes by the thermal decomposition of Mo(CO)6 by Menachem Motiei; Jose Calderon-Moreno; Aharon Gedanken (267-271).
Multiwalled carbon nanotubes (MWCNTs) have been obtained by decomposing molybdenum hexacarbonyl under air or argon in a closed cell. In addition to the carbon nanotubes (CNTs), Mo2C was obtained. A high percentage of CNT was obtained from only a few graphitic carbon particles. Our proposed mechanism suggests that CNT is formed via the Boudard reaction as well as by the reduction of CO by Mo.

The ultrafast charge transfer (CT) dynamics in two directly linked pyrenyl donor–acceptor systems has been studied using femtosecond broadband pump–probe spectroscopy. This method allows to capture complex chemical dynamics by measuring the time-resolved spectral evolution of transient absorption and stimulated emission induced by femtosecond optical pumping. After electronic relaxation, an optical CT transition between two excited states was found in both systems. Although the excited state CT occurs adiabatically significant differences in the electronic coupling are deduced from the band intensities. The results are discussed in terms of an adiabatic state model and compared with predictions from orbital topology arguments.

The N–H⋯OC proton transfer in aqueous solution: a suitable procedure for extracting atomic charges by S. Tolosa Arroyo; J.A. Sansón Martı́n; A. Hidalgo Garcı́a (279-286).
Molecular dynamics simulation is used to study how the solute–solvent potential affects the classical free energy surfaces of the reactant and product states in the N–H⋯OC proton transfer process in an aqueous medium when the atomic charges that describe the electrostatic contribution of the potential are modified. The strong dependence of the thermodynamic properties (ΔG,ΔG r, and ΔG # free energies) associated with the proton transfer on the charge definition employed led us to look for a new procedure to calculate the atomic charges which is better suited to the method used in the determination of the free energy curves via the solute–solvent interaction energy.

The possibility of storing the mixture of H2 and CH4 in a complex sorbent composed of superactivated carbon and TiMn1.5 alloy was experimentally studied. The storage capacity of the complex sorbent was shown nearly equal to the sum of the storage capacity of the component sorbents. Therefore, sorptive storage is technically feasible for a clean fuel mixed with natural gas and hydrogen. As a consequence, the storage pressure is considerably decreased comparing to that of compression technology.

Trans-gauche isomerization in 1-octanol probed by Brillouin scattering spectroscopy by Paola Sassi; Marco Paolantoni; Assunta Morresi (293-296).
The results of a Rayleigh–Brillouin (RB) experiment performed on 1-octanol in the 10–80 °C temperature range are presented and discussed. Two different relaxation processes at the temperatures of 30 and 50 °C ca. are described in terms of relaxation times and activation energies. The comparison between our experimental results and existing literature data suggests the possible interpretation of the general dynamical behavior of n-alcohols in the gigahertz frequency range.

Bundles of single-walled carbon nanotubes (SWNTs) with a narrower distribution of diameter have been produced by catalytic decomposition of methane at 1010 °C on a newly developed catalyst LaFeO3. The SWNTs were characterized by means of transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. The diameter of the SWNTs is in the range of 0.8–1.8 nm. This result shows for the first time that SWNTs could be produced by catalytic decomposition of hydrocarbons without Al2O3, or SiO2 or MgO support.

Symmetry-adapted perturbation theory based on Kohn–Sham determinants, SAPT(KS), was shown before to perform poorly for the electrostatic energy which is potentially exact in this approach. We demonstrate that some deficiencies of SAPT(KS) result from wrong asymptotics of exchange-correlation potentials. On applying an asymptotic correction, we were not only able to recover the electrostatics, but also the first-order exchange and second-order induction and exchange-induction energies fairly accurate. Dispersion is still reproduced poorly but can be computed reasonably accurately from the damped asymptotic expansion.

Structural stability of the rhombohedral 2D polymeric phase of C60 studied by in situ Raman scattering at pressures up to 30 GPa by K.P. Meletov; J. Arvanitidis; G.A. Kourouklis; K. Prassides; Y. Iwasa (307-313).
The structural stability of the rhombohedral two-dimensional (2D) polymeric phase of C60 has been studied as a function of pressure up to ∼30 GPa at room temperature by means of in situ Raman scattering. An irreversible transformation to a new disordered phase was observed at a pressure of ∼15 GPa. The intensity of the Ag(2) pentagonal pinch (PP) mode rapidly decreases in the pre-transitional pressure range while the Raman spectrum of the transformed material becomes very diffuse. The high-pressure phase recovered to normal conditions is metastable and transforms under heating to a mixture of pristine and dimerized C60 as can be seen by their Raman spectra. The retention of the fullerene molecular cage at high pressure and quenching of the PP-mode are the indications that the high-pressure phase may be associated with a random creation of new polymeric bonds between the molecules in adjacent polymeric planes of the 2D-rhombohedral phase of C60.

Catalytic growth and photoluminescence properties of semiconductor single-crystal ZnS nanowires by Yewu Wang; Lide Zhang; Changhao Liang; Guozhong Wang; Xinsheng Peng (314-318).
Semiconductor single-crystal ZnS nanowires have been successfully synthesized in bulk quantities by a new, simple and low cost process based on thermal evaporation of ZnS powders onto a silicon substrate with the presence of Au catalyst. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) observations show that the ZnS nanowires have diameters about 30–60 nm and lengths up to several tens micrometers. The growth of ZnS nanowires is controlled by the conventional vapor–liquid–solid (VLS) mechanism. And the photoluminescence (PL) properties of these synthesized single-crystal ZnS nanowires have been presented in this Letter.

The CCSD(T) method has been used to compute a highly accurate quartic force field and fundamental frequencies for all 14 N and 15 N isotopomers of the high energy density material TdN4. The computed fundamental frequencies show beyond doubt that the bands observed in a matrix isolation experiment by Radziszewski and coworkers [Chem. Phys. Lett. 328 (2000) 227] are not due to different isotopomers of TdN4. The most sophisticated thermochemical calculations to date yield a 2N2→N4 heat of reaction of 182.22±0.5 kcal/mol at 0 K (180.64±0.5 at 298 K). It is hoped that the data reported herein will aid in the ultimate detection of TdN4.