Chemical Physics Letters (v.366, #5-6)

We calculate positions and predissociation widths for quasi-bound states of HOCl with total angular momentum of J=0 and J=3. An ab initio potential energy surface is used in conjunction with a complex absorbing potential (CAP). These calculations are performed by diagonalising a complex symmetric Hamiltonian using our discrete variable representation (DVR) based parallel code, PDVR3D, and a truncation and diagonalisation algorithm. The resonances are identified as those states in the continuum, which are stable with respect to CAP and basis set parameters. Test on the resonances are carried out using over 90 different absorbing potential heights. Resonances of both Feshbach (vibrational trapping) and shape (rotational trapping) are identified.

Selective synthesis of zigzag-type aligned carbon nanotubes on SiC (0 0 0 −1) wafers by M Kusunoki; T Suzuki; C Honjo; T Hirayama; N Shibata (458-462).
Zigzag-type carbon nanotubes have been selectively produced by surface decomposition of a well-polished SiC single crystal. The SiC wafer was heated to 1500 °C at a very small heating rate under vacuum. Transmission electron microscopy (TEM) and electron diffraction patterns revealed that almost all the well-aligned carbon nanotubes formed perpendicular to the SiC (0 0 0 −1) surface were double-walled and of zigzag type. The results of high-resolution electron microscopy (HREM) indicate that the zigzag type structure evolves from the Si–C hexagonal networks in the SiC crystal by the collapse of carbon layers remaining after the process of decomposition.

Cluster-mediated filling of water vapor in intratube and interstitial nanospaces of single-wall carbon nanohorns by E Bekyarova; Y Hanzawa; K Kaneko; J Silvestre-Albero; A Sepulveda-Escribano; F Rodriguez-Reinoso; D Kasuya; M Yudasaka; S Iijima (463-468).
This study reports experimental data of water adsorption at 303 K on single-wall carbon nanohorns (SWNHs). The analysis of the water adsorption isotherms supports a cluster-mediated model for filling the interstitial and intratube nanospaces in contrast to the monolayer formation observed for simple nonpolar molecules. The enthalpies of water immersion of SWNHs with closed and open nanohorns show a very week interaction between the water molecules and the hydrophobic carbon nanotubular structure; the observed specific enthalpy of immersion expressed per unit surface area is lower than the reported values for graphite.

Order-selective multiple-quantum excitation in magic-angle spinning nuclear magnetic resonance is explored using a class of symmetry-based pulse sequences, denoted SM χ . Simple rules are presented that aid the design of SM χ schemes with certain desirable effective Hamiltonians. They are applied to construct sequences generating trilinear effective dipolar Hamiltonians, suitable for efficient excitation of triple-quantum coherences in rotating solids. The new sequences are investigated numerically and demonstrated by 1 H experiments on adamantane.

Absorption oscillator strengths for electronic transitions involving Rydberg series (including the continuum) of formaldehyde, carbonyl fluoride and phosgene have been calculated with the molecular-adapted quantum defect orbital (MQDO) procedure. These compounds are known to play an important role in the evolution of the interstellar medium and the Earth’s upper atmosphere. The results have been analysed on the grounds of the scarce comparative data found in the literature and by compliance with continuity across the ionisation threshold. The similarities observed between the calculated intensities of analogous transitions in the isovalent molecules F2CO and Cl2CO have served the purpose of assessing the quality of our calculations. New data, which may aid in future experimental measurements, are supplied.

Thin films of CuI were prepared by pulse laser deposition technique and their characteristics are studied. These films exhibited optical transmittance over 80% in the wavelength range 400–900 nm and minimum resistivity of about 2 K Ω cm. Blue shift in the onset of optical absorption of the CuI films is observed to that of polycrystalline powder of CuI.

A method of generation of intense pulsed molecular beams of low kinetic energy is suggested. The method is based on formation of a cold pressure shock in front of a solid surface and using it as a source for generation of low-energy beams. The pressure shock is formed when an intensive pulsed gas dynamically cold supersonic molecular beam interacts with the surface. The molecular beams of H2, He, CH4 and Kr with kinetic energy ⩽10 meV and the molecular beams of H2/Kr and He/Kr with kinetic energy of H2 and He ⩽0.3 and ⩽0.6 meV accordingly were obtained.

Local self-interaction-free approximate exchange-correlation potentials are derived and applied in the Levy–Nagy variational density functional theory for individual excited states. The self-interaction-corrected (SIC) local von Barth–Hedin and Vosko–Wilk–Nusair potentials are studied for excited states of some atoms and ions. Accurate ionization energies and correct asymptotic decay of excited SIC potentials are observed. Approximate validity of Koopmans’ theorem for excited states are shown.

The stability of novel, low dimensional, crystal structures formed by a simple alkali halide (KI) in single-walled carbon nanotubes are investigated using a simple computer simulation model. ‘Twisted’ crystals, not clearly related to the bulk structure, and found to form dynamically in specific tube diameters, are investigated. A phase diagram for the confined structures as a function of the nanotube pore size is calculated. Specific ranges of nanotube diameters are shown to favour these unique structures over structures related directly to those adopted by the bulk alkali halide. The high resolution transmission electron microscopy pattern for an example stable twisted crystal is simulated.

The formation of cyclopentenyl cation from (i) dissociation of ionized cyclohexene, and, (ii) ion–molecule reaction between ionized 1,3-butadiene and ethylene is confirmed by means of the corresponding thermochemistry. Measurement of the Gibbs free energy and enthalpy for deprotonation of cyclopentenyl cation is provided by Fourier transform ion cyclotron resonance experiments and use of the thermokinetic method. The values (GB=795.0±1.2 and PA=824.9±1.1  kJ/mol , respectively) allow the determination of the heat of formation of the cyclopentenyl cation to be 840.6±4.1  kJ/mol in good agreement with existing data.

The energy of NS was computed via CCSD(T) theory, together with extrapolation to the complete basis set limit and corrections for anharmonic zero-point energy, scalar and vector relativistic terms, and core–valence electron correlation. The results were employed with three working reactions to find Δ f H0(NS)=277.3±2  kJ mol −1 and Δ f H298(NS)=278.0±2  kJ mol −1 . This thermochemistry is consistent with, but much more precise than, earlier literature values.

In LIF (laser-induced fluorescence) excitation and hole-burning spectra of a merocyanine dye, EtMD, in a supersonic jet, bands due to one of the four possible isomers were observed. Only lower-frequency vibronic bands were observed in the LIF-excitation spectra, while broad and deep dips were observed in the higher energy region of the hole-burning spectra where no LIF bands were observed. The LIF bands were found to consist of two transition systems, which are presumably due to the molecules in the ground and low-lying excited vibrational states. Possible relaxation processes of EtMD in the excited electronic state were discussed.

A continuous liquid flow of an aqueous solution of phenol (Ph) in a vacuum (a liquid beam) was irradiated with a pulsed IR laser at 3 μm, which was resonant to the OH-stretching vibration of the solvent water molecules. Phenol molecules ejected from the liquid beam were selectively ionized at about 0.5 mm above it by a pulsed UV laser (270–280 nm). The photoions thus produced were extracted in a pulsed electric field with a given residence time after the photoionization for mass analysis. It was shown that photoions, Ph+, were solvated into Ph+(H2O) n in a dense cloud of water vapor ejected from the liquid beam by IR irradiation.

A less expensive Ewald lattice sum by Dean R Wheeler; John Newman (537-543).
We present a treatment of the Ewald lattice sum which permits 25% or more decrease in program execution cost for the same level of accuracy. This is accomplished by optimizing on additional degrees of freedom introduced into the function that partitions the Coulombic potential between real- and reciprocal-space parts. The technique was tested in simulations of 1 M KCl in water. It is relatively simple to implement in existing codes, including those based on fast-Fourier-transform solutions to the lattice sum.

Bamboo-shaped carbon tubes from coal by Y.F Li; J.S Qiu; Z.B Zhao; T.H Wang; Y.P Wang; W Li (544-550).
Bamboo-shaped carbon tubes (BCTs) were first synthesized in high yields from iron-loaded carbon electrodes prepared from coal by arc discharge. The BCTs were characterized by scanning electron microscopy and transmission electron microscopy (TEM). The TEM characterization reveals that the tubes have bamboo-like structures consisting of hollow compartments separated with conical shaped graphite layers. The diameters of BCTs are in the range of 40–60 nm with their length being about several micrometers. For some BCTs, the hollow compartments are quite uniform with a size of 100 nm. A growth model is suggested to explain the formation of bamboo structure in tubes.

Size-dependent cohesive energy of nanocrystals by Q Jiang; J.C Li; B.Q Chi (551-554).
Our simple model for the size dependence of latent heat, free of any adjustable parameter, has been extended for the size dependence of cohesive energy, or boiling heat. The cohesive energy decreases strongly when the size of particles decreases to several nanometers. The model prediction is found to be in agreement with the experimental results of W and Mo nanoparticles.

Bulk production of multi-wall carbon nanotube bundles on sol–gel prepared catalyst by Yuesheng Ning; Xiaobin Zhang; Youwen Wang; Yanlin Sun; Lihua Shen; Xiaofang Yang; G Van Tendeloo (555-560).
A method to grow multi-wall carbon nanotube bundles in a high yield (weighing over 15 times the catalyst) is developed and a plausible explanation for the formation and high yield of the bundles is suggested. The Co–Mo–Mg–O catalyst used in the experiment is prepared by a sol–gel technique, molybdenum being doped into the catalyst through oxidation and diffusion at 750 °C. Small changes to the catalyst preparation lead to the growth of single-wall carbon nanotubes (SWNTs). Our work is an exploitation of the high performance of the solid catalyst in the synthesis of novel nanomaterials.

Formation of Pd n (SR) m clusters (n<60) in the reactions of PdCl2 and RSH (R=n-C18H37, n-C12H25) by Yuichi Negishi; Haruno Murayama; Tatsuya Tsukuda (561-566).
Mass spectroscopic analysis revealed that Pd clusters passivated by thiolates and the stoichiometric thiolate complexes, Pd n(SR)2n  (n=5,6), are formed in the reactions between palladium chloride and n-alkanethiols (RSH: R=n-C18H37, n-C12H25) in toluene. The Pd clusters thus formed are formulated as Pd n (SR) m with m∼0.6n. The cluster sizes, distributed in the range of 5⩽n⩽60, are consistent with their core diameters of ∼1 nm observed by TEM. A gap of ∼2 eV was observed in the optical transition of the Pd n (SR) m clusters showing the emergence of non-metallic properties as a result of size reduction.

Fabrication of CoO nanorods via thermal decomposition of CoC2O4 precursor by Congkang Xu; Yingkai Liu; Guoding Xu; Guanghou Wang (567-571).
Cobalt oxide (CoO) nanorods were synthesized by annealing CoC2O4 precursor. The nanorods were identified by Transmission electron microscopy (TEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and other methods. The results showed that the nanorods are composed of cubic CoO with diameter of 10–80 nm, and lengths ranging from 1 to 3 μm. The mechanism of formation of CoO nanorods was also discussed.

Metal dispersed activated carbon fibers and their application for removal of SO x by Ikpyo Hong; Hancheng Jiang; Yang-Duk Park; Je-Young Kim; Baik-Hyon Ha (572-577).
Uniformly metal dispersed ACFs were prepared by mixing organometallic compounds with THF and pitch. The solvent was removed from this mixture and then pitch was spun, stabilized, carbonized and activated. The specific surface areas and pore size distributions of prepared ACFs and DeSO x catalytic reactivities were determined. The mesopores of ACF were developed by the addition of Co, Ni, Mn. The DeSO x catalytic reactivity of Ni, Pd, Co, V and Cr dispersed ACFs demonstrated much higher continuous reaction conversion than reference pitch-ACF.

Ab-initio quantum mechanical calculation is used to calculate the 14N and 2H nuclear quadrupole resonance (NQR) parameters (η and χ) of CH3N2 + ion and the ion shellvated by H2 molecules [CH3N2 +(H2) n=1–9]. On the basis of NQR parameters, three distinct shells (A, B and C) were identified. To obtain these data we had to evaluate the electric field gradient (EFG) around any atom in each situation. EFG’s were calculated by the Gaussian 98 program using the MP2/6-311G** method.

Bound energy levels at the n=2 dissociation threshold in HD by Th.G.P Pielage; A de Lange; F Brandi; W Ubachs (583-587).
Level energies of g symmetry states lying just below the n=2 dissociation threshold have been determined in a XUV + IR multi-step laser excitation experiment in HD, with an absolute accuracy of the excitation energy of 0.015 cm−1. Intermediate B 1 Σ u + energy levels have been calibrated by measuring transition frequencies in the B 1 Σ u +–X 1 Σ g +(16,0) Lyman band with an accuracy of 0.007 cm−1. It is shown that v=3 is the highest bound vibrational level in the shallow I 1 Π g outer well potential in HD, and that only two rotational levels exist.

We show that the off-diagonal coherence peaks in two-dimensional Fourier transform NMR spectroscopy of fluids contained in porous media undergoing magic angle sample spinning (MASS) arise from amplitude modulation of the fluid’s magnetization. The amplitude modulation originates from the combined effect of MASS and the molecular diffusion through the inhomogeneous magnetic fields created by the susceptibility contrasts in the porous medium. The magnitude of the off-diagonal peaks provides information on the porous medium’s structural length scales, which give rise to correlation length scales of the magnetic susceptibility.

The anisotropy of the ionic photofragments produced from SF6 has been measured using synchrotron radiation in the range of 23–210 eV. Despite the highly symmetrical molecule a strong anisotropy is observed below ∼35 eV. The behavior of the asymmetry parameter involving all the fragment ions has been interpreted by simulation using partial oscillator strengths for the formation of individual species. Only SF5 + ions produced via superexcited states of valence type are assumed to have an anisotropic angular distribution. The observed decrease in the asymmetry parameter with increasing photon energy can be ascribed to the dominance of direct photoionization and the decrease in the branching ratio for SF5 + formation.

Nuclear mass corrections for atoms and ions by Toshikatsu Koga; Hisashi Matsuyama (601-605).
To take the nuclear motion contribution into account, we traditionally evaluate the normal mass ε nm and specific mass (mass polarization) ε sm corrections separately and add them to the total electronic energy of atoms and ions calculated in the fixed-nucleus approximation. We point out that the sum of these mass corrections ε mass=ε nm+ε sm is immediately and rigorously obtained from the electron-pair moments in momentum space. The Hartree–Fock limit values of the mass correction sum ε mass are reported for the 102 neutral atoms He through Lr, singly charged 53 cations Li+ through Cs+, and 43 stable anions H through I in their experimental ground states.

Impulsive excitation of a vibrational mode of Cs on Pt(1 1 1) by Kazuya Watanabe; Noriaki Takagi; Yoshiyasu Matsumoto (606-610).
We demonstrate the real time observation of coherent vibrational motions of Cs atoms adsorbed on Pt(1 1 1). A femtosecond laser pulse excites impulsively a Cs–Pt stretching mode and the subsequent evolution of the nuclear motion of Cs atoms is probed by measuring the oscillatory modulation of the second harmonic intensity of a probe pulse as a function of the pump–probe delay. The frequency and the dephasing time of the mode are found to be 2.3 THz and 1.4 ps, respectively.

We report an extension of the local correlation concept to electronically excited states via the equation-of-motion coupled cluster singles and doubles (EOM-CCSD) method. We apply the same orbital domain structure used successfully for ground-state CCSD by Werner and co-workers and find that the resulting localized excitation energies are in error generally by less than 0.2 eV relative to their canonical EOM-CCSD counterparts, provided the basis set is flexible and includes Rydberg-like functions. In addition, we account for weak-pair contributions efficiently using a correction to local-EOM-CCSD transition energies based on the perturbative (D) correction used with configuration interaction singles (CIS).

Ab initio study of Eu3+–L (L=H2O, H2S, NH2CH3, S(CH3)2, imidazole) complexes by Alessandra Ricca; Charles W Bauschlicher (623-627).
The ground states and binding energies of Eu3+–L (L=H2O,H2S,NH2CH3,S(CH3)2, imidazole) complexes has been determined using ab initio techniques. The binding is mostly electrostatic as expected. The empty f orbital is different for the S compounds, being a π-like orbital, while for the O and N containing ligands it is a σ-like orbital. However, the range in the binding energies for the different f holes is small.

Spectral characteristics of 6-hydroxyquinoline (6-HQ) in presence of trimethylamine (TMA) were investigated in polar and non-polar solvents. The steady-state absorption, emission and excitation spectra along with the transient parameters reveal a strong ground state hydrogen-bonded complex formation between the 6-HQ and TMA molecules in both the media. A large Stokes shifted emission due to the formation of contact ion-pairs is observed in these media. However, in acetonitrile the longer decay time (≈12 ns) with relatively broadened emission spectra can be attributed to the presence of solvent separated ion-pairs in addition to contact ion-pairs. The ground state equilibrium constant for complex formation has been determined. The observed quenching behaviour of the fluorescence emission from the normal molecule with TMA appears to be static in nature.

Near-edge X-ray absorption fine structure study of helicity and defects in carbon nanotubes by Y.H Tang; T.K Sham; Y.F Hu; C.S Lee; S.T Lee (636-641).
The chemical bonding and electronic structure of carbon nanotubes were investigated with high-resolution C K-edge near-edge X-ray absorption fine structures using total electron yield and fluorescence yield. The measurements probe the densities of state above the Fermi level. The newly observed peaks at 284.5 and 290.5 eV are attributed to the rolling of the carbon layers and defects of the nanotubes, respectively. The high-resolution C K-edge spectra of carbon nanotubes are of fundamental interest to the properties and analysis of carbon nanotube.

Dissociation dynamics and stability of cyclopentoxy and cyclopentoxide by Leah S Alconcel; Robert E Continetti (642-649).
Cyclopentoxide c-C5H9O undergoes photodetachment to stable cyclopentoxy or the ring-opened 5-oxo-pentan-1-yl radical and dissociative photodetachment, yielding C3H5O and C2H4 photofragments, at both 532 and 355 nm. The adiabatic electron affinity of c-C5H9O is estimated from the experimental results and ab intio calculations to be 1.5±0.1 eV. The results show that c-C5H9O is stable relative to dissociation into C3H5O and C2H4 by 1.23±0.07  eV , whereas c-C5H9O is unstable relative to C3H5O and C2H4 by −0.12±0.12  eV . These results are discussed in terms of the factors affecting the stability of cyclic alkoxides and the corresponding alkoxy radicals.

The dissociative photodetachment dynamics of (SO2)3 were studied by photoelectron–photofragment coincidence spectroscopy at 258 nm. Correlation between the photoelectron and photofragment translational energies was observed as previously seen in the dimer system, implying the presence of a dimer core. The three-body dissociation dynamics of (SO2)3 after photodetachment are consistent with a dimer core solvated by a spectator SO2 molecule with a broad distribution in initial geometry.

We have obtained transient resonance Raman spectra of the [CH2CHCH2]+ (allyl cation) produced following C-band excitation of cyclopropyl bromide. The experimental resonance Raman spectrum display an overtone progression in the nominal [CCC]+ stretch mode and its combination bands with the CH/CH2 rocking modes. Density functional theory computations were performed to estimate the vibrational frequencies for the allyl cation, the allyl radical, the cyclopropyl radical, the cyclopropyl bromide molecule and the gauche-allyl bromide molecule and compared to the experimental vibrational frequencies. This comparison indicates that the allyl cation can be formed as a product of cyclopropyl bromide photodissociation in acetonitrile solution.

Formation of carbon nanotubes in water by the electric-arc technique by H.W Zhu; X.S Li; B Jiang; C.L Xu; Y.F Zhu; D.H Wu; X.H Chen (664-669).
A simplified arc discharge apparatus was used for growing carbon nanotubes, required only water (solution) in a glass container with no need for vacuum, water-cooled chamber. Carbon nanotubes with highest purity (20%) and highest yield (7 mg/min) were obtained when using salt solution as the medium. Resonance Raman spectrum of multi-walled carbon nanotubes (MWNTs) presented in as-grown materials was measured and RBM peaks originating from very thin core nanotubes were observed. The results show that high-quality MWNTs can be effectively prepared in water-arcing process.

We investigated the effect of amino acids in rhodopsin on the protonation state of the Schiff base (SB) retinal. We constructed a model system consisting of SB retinal, Glu113 (counterion), and eight residues. For this model, we considered two states of the SB retinal, namely, the protonated/deprotonated state. We then performed ab initio MO calculations at the RHF/6-31g* level. As a result, the protonated state was stabler than the deprotonated state. Interestingly, we observed an additive rule for the contribution to the stabilization energy due to each amino acid. Above all, it turned out that Ser186 and Cys187 play a significant role in the stability.

The mechanism of the reaction between O(1 D) and NF3, experimentally studied by spectroscopic techniques [V.I. Sorokin, N.P. Gritsan, A.I. Chichinin, J. Chem. Phys. 108 (1998) 8995], has been investigated at the Coupled Cluster level of theory in conjunction with double-zeta and triple-zeta quality basis sets. The process commences by the exoergic (105.4 kcal mol −1 ) formation, on the singlet surface, of the O–NF3 intermediate, whose eventual dissociation into NF2 and OF passes through the isomerization to F2N–OF. The energy barrier of this process, 58.8 kcal mol −1 , is significantly lower than the intersystem crossing from the singlet O–NF3 to the triplet O(3 P) and NF3 dissociation products. This is consistent with the experimental observation that, in the reaction between O(1 D) and NF3, the unreactive quenching to O(3 P) represents only a minor reaction channel.

Periodic ab initio B3-LYP calculations on the MgO(0 0 1)/CO system underestimate the CO binding energy value with respect to experiment. The flaw is in the B3-LYP functional, unable to compute dispersive interactions. Here we show how to evaluate this contribution by adopting a two-layer ONIOM scheme in which the B3-LYP crystal energy is improved by the MP2 energy computed on the Mg9O9/CO cluster. The final complete basis set extrapolated (MP2/∞:B3-LYP/VTZ) CO/Mg(0 0 1) binding energy of 13 kJ/mol is in good agreement with experiment, with about 7 kJ/mol deriving from dispersive interactions.

Author Index (691-702).