Chemical Physics Letters (v.372, #3-4)
Velocity- and mass-resolved REMPI spectroscopy of van der Waals molecules. A technique for determining the cluster size responsible for spectral features by Rebecca K Sampson; Susan M Bellm; Jason R Gascooke; Warren D Lawrance (307-313).
An experimental method is presented for assigning vibronic spectra of van der Waals molecules based on the measurement of the velocity- and mass-resolved resonance enhanced multiphoton ionisation (VMR-REMPI) spectrum. The basis of the technique is that at each wavelength one measures the velocity map image of the ions produced at a chosen mass. If this mass corresponds to the parent ion for the transition, the image shows a central spot only. However, if this mass is from a fragment ion, the image is enlarged due to the velocity gained by the ion during dissociation. VMR-REMPI spectra consist of plots of the integrated signal in an appropriate image area versus laser wavelength or frequency. The technique is demonstrated with two examples, benzene–acetylene n (n=1–3) and p-difluorobenzene–Ar. Application of the technique to the former system leads to a reassignment of the spectrum.
Contributions of steady heat conduction to the rate of chemical reaction by Hyeon-Deuk Kim; Hisao Hayakawa (314-319).
We have derived the effect of steady heat flux on the rate of chemical reaction based on the line-of-centers model using the explicit velocity distribution function of the steady-state Boltzmann equation for hard-sphere molecules to second order. It is found that the second-order velocity distribution function plays an essential role for the calculation of it. We have also compared our result with those from the steady-state Bhatnagar–Gross–Krook (BGK) equation and information theory, and found no qualitative differences among them.
A soft X-ray absorption study of nanodiamond films prepared by hot-filament chemical vapor deposition by Y.H Tang; X.T Zhou; Y.F Hu; C.S Lee; S.T Lee; T.K Sham (320-324).
Nanodiamond films synthesized by a hot-filament chemical-vapor-deposition method using a methane–hydrogen mixture have been investigated with near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The carbon K-edge NEXAFS of the nanodiamond film exhibits a blue-shifted exciton peak and absorption threshold relative to that of the CVD diamond film. These features are characteristic of quantum confinement behavior. This observation confirms the presence of a nanodiamond film as was revealed by transmission electron spectroscopy. The results show that the correlation of the blue shift with the grain size of the nanodiamond is in the same direction but smaller than results previously reported in the literature.
129Xe chemical shift measurements on a single crystal surface by H.J Jänsch; P Gerhard; M Koch; D Stahl (325-330).
Nuclear magnetic resonance spectroscopy has been performed on xenon adsorbates on a iridium single crystal surface. Optical pumping methods have been applied to increase the 129Xe polarization and thus the NMR sensitivity by five orders of magnitude. Enriched 129Xe gas has been adsorbed on a carbon monoxide and ethylidyne covered Ir(1 1 1) surface with coverages up to one monolayer. In addition the surface of a condensed xenon bulk has been investigated. Narrow resonances with distinct chemical shifts were observed reflecting the very different nature of the substrates. This opens a new field of spectroscopy for the study of surfaces.
The photo-electronic transfer across membrane between C60 and CdS nanoparticles by Lianying Wang; Xingtang Zhang; Zuliang Du; Yubai Bai; Tiejin Li (331-335).
The photoelectric property of the composite assembly of C60 and CdS nanoparticles fabricated by LB technique was studied. The luminescence of CdS nanoparticles band–band exciton emission was extremely quenched resulted from the photocharge transfer from CdS nanoparticles to C60 across a lipidic layer (about 2–3 nm). The fatty layer between C60 and CdS nanoparticles played an important role in preventing photocharge recombination in their composite assemblies.
The surface decoration and electrochemical hydrogen storage of carbon nanofibers by Xiaoqi Yan; Xueping Gao; Ying Li; Zhanquan Liu; Feng Wu; Yutian Shen; Deying Song (336-341).
The tube-like CNFs with cone-shaped structure were synthesized by catalytic pyrolysis of methane. The outer surface of purified CNFs was decorated with Ni–P alloy particles having polycrystalline or nanocrystalline structure instead of amorphous structure. The low Ni–P content appeared to be more efficient to cover the outer surface of CNFs. The electrochemical discharge capacity increased with increasing the Ni–P content on the outer surface of CNFs owing to the synergistic effect between metal and carbon in the electrochemical reaction. The heat treatment contributed to the higher crystallization of surface alloy and improvement of the electrochemical capacity of the composite.
Fragment molecular orbital method: application to molecular dynamics simulation, ‘ab initio FMO-MD’ by Yuto Komeiji; Tatsuya Nakano; Kaori Fukuzawa; Yutaka Ueno; Yuichi Inadomi; Tadashi Nemoto; Masami Uebayasi; Dmitri G. Fedorov; Kazuo Kitaura (342-347).
A quantum molecular simulation method applicable to biological molecules is proposed. Ab initio fragment molecular orbital method-based molecular dynamics (FMO-MD) combines molecular dynamics simulation with the ab initio fragment molecular orbital method. Here, FMO computes the force acting on each atom’s nucleus while MD computes the nuclei’s time-dependent evolutions. FMO-MD successfully simulated a small polypeptide, demonstrating the method’s applicability to biological molecules.
Theoretical study of nonadiabatic transitions in the photodissociation of Cl2 and Br2 by Yukako Asano; Satoshi Yabushita (348-354).
Lower-lying potential curves of Br2 are calculated by the spin–orbit configuration interaction method, and the spin–orbit branching mechanisms in the photodissociation processes are examined. The second absorption band at 227 nm is assigned unambiguously to the transition from the X 1 Σ + g to the 3 Σ + 1u (σ g→σ u *) state. The calculated potential curves and the radial derivative coupling elements of Cl2 and Br2 are used to evaluate the nonadiabatic transition probabilities by solving the time-dependent coupled Schrödinger equations semiclassically. The different nonadiabatic behavior in Cl2 and Br2 is analyzed in terms of the differences in the electronic factors and the reduced mass.
Ab initio study on the ground and low-lying excited states of GaH by Xinzheng Yang; Meirong Lin; Wenli Zou; Baozheng Zhang (355-361).
A multireference configuration interaction (MRCI) study has been carried out on GaH. Potential energy curves and spectroscopic constants of the X 1 Σ 0+ + , a 3 Π 0−,0+,1,2 , A 1 Π 1 and a Rydberg state of 1 Σ + (II) are obtained. The observed open-structure absorption bands of GaH in the region 41 650–46 300 cm−1 can be ascribed to the transitions from this Rydberg state at about 45 000 cm−1 to the ground state. Breit–Pauli operator is used for spin–orbit coupling effect calculations. Four Ω components of the bound a 3 Π 0−,0+,1,2 state are calculated for the first time. The transition properties of the excited states, including the transition dipole moments, the radiative lifetimes and the Franck–Condon factors, are predicted.
Comparison of the T 1 and D 1 diagnostics for electronic structure theory: a new definition for the open-shell D 1 diagnostic by Timothy J Lee (362-367).
It is shown that the coupled-cluster T 1 operator used in a previous study to define the open-shell D 1 diagnostic is ill defined, and leads to an arbitrary definition of the open-shell D 1 diagnostic. A new definition is proposed that eliminates this ambiguity and approximately restores the mathematical relationship previously noted between the closed-shell D 1 and T 1 diagnostics. Statistical comparison of the T 1 and D 1 diagnostics shows a very high degree of correlation between them for the molecular systems studied thus far, although it is argued that both diagnostics used together can provide more information than either can separately.
Ultraviolet light-induced spectral change in cubic nanocrystalline Y2O3:Eu3+ by Hongwei Song; Baojiu Chen; Baojuan Sun; Jisen Zhang; Shaozhe Lu (368-372).
Ultraviolet light-irradiation induced spectral change was studied in cubic nanocrystalline Y2O3:Eu3+. Under the irradiation of the ultraviolet lights separated from xenon lamp, the excited charge transfer band of Eu3+ decreased after irradiation. The smaller the particle size and the shorter the wavelength, the larger the spectral change. It was attributed to the local structural change surrounding Eu3+ ions in/near the surface. Under the irradiation of the 266-nm pulsed laser, some Eu3+ in nanoparticles was reduced to Eu2+.
Bulk modulus of solid deuterium at 15 K by Haruki Kawamura; Yuichi Akahama; Yasuo Ohishi; Osamu Shimomura; Kenichi Takemura (373-376).
X-ray powder diffraction experiments for solid n-D2 at 15 K were performed at pressures up to 57 GPa. In phase II, as well as in phase I, the center of each deuterium molecule is located on an hcp lattice point. The bulk modulus (K 0) and its pressure derivative (K 0 ′) at 15 K were determined as 0.386(23) GPa and 6.43(10), respectively.
Sternheimer shieldings and EFG polarizabilities: a density-functional theory study by Antonio Rizzo; Kenneth Ruud; Trygve Helgaker; Paweł Sałek; Hans Ågren; Olav Vahtras (377-385).
The electric field gradient (EFG) at the nucleus, the generalized Sternheimer shielding constants, and the EFG hyperpolarizabilities of a set of reference molecules are computed using analytic density-functional (up to quadratic) response theory. At the three-parameter Becke–Lee–Yang–Parr (B3LYP) level, density functional theory (DFT) underestimates correlation effects compared with other approaches such as coupled-cluster and multiconfigurational self-consistent field. For the prediction of EFG properties of hydrogen nuclei and electron-rich atoms such as halides, DFT/B3LYP provides results even less reliable than Hartree–Fock theory.
Two-photon absorption properties of symmetric substituted diacetylene: drastic enhancement of the cross section near the one-photon absorption peak by Kenji Kamada; Koji Ohta; Yoichiro Iwase; Koichi Kondo (386-393).
Two-photon absorption (TPA) spectra are presented for newly synthesized bis(pyridylstyryl)-substituted diacetylene and related methyl triflate derivatives. The TPA cross section of a derivative (MPPBT) was found to increase drastically with decreasing the incident wavelength below 650 nm and to reach (2.42±0.46)×10−47 cm 4 s molecule −1 photon −1 at 571 nm, in addition to the weaker, lowest energy TPA peak centered at 764 nm. A four-state model was needed to account for the observed spectral shape, suggesting that the drastic enhancement is due to one-photon resonance enhancement not only of the lowest energy TPA transition but also of a higher energy two-photon transition.
Metal-doped germanium clusters MGe n s at the sizes of n=12 and 10: divergence of growth patterns from the MSi n clusters by Jing Lu; Shigeru Nagase (394-398).
Structural and electronic properties of the metal-doped germanium clusters MGe n s (M = Hf, W, Os, Ni, and Zn) in the sizes of n=12 and 10 are investigated via density functional theory calculations based on the hybrid exchange-correlation energy. Their growth patterns are found different from those of the MSi n clusters although the pure Ge n and Si n clusters have identical geometries in the two sizes. The MGe12 (M = W and Os) and ZnGe12 clusters, with an endohedral distorted hexagonal prismatic and an endohedral perfect icosahedral structure, respectively, show higher chemical stability among these checked MGe n clusters. This makes them attractive for cluster-assembled materials.
Continuous carbon nanotube production in underwater AC electric arc by L.P. Biró; Z.E. Horváth; L. Szalmás; K. Kertész; F. Wéber; G. Juhász; G. Radnóczi; J. Gyulai (399-402).
A simple, low cost and continuous growth method for the production of well graphitized multi-wall carbon nanotubes is described. The growth takes place in an AC arc in water between two carbon electrodes. At a voltage of 40 V the arc is stable in the range of 85–45 A, lower current values help in increasing the fraction of carbon nanotubes in the product.
Electron-vibrational relaxation of photoexcited polyfluorenes in the presence of chemical defects: A theoretical study by Ignacio Franco; Sergei Tretiak (403-408).
A quantum chemical semiempirical investigation of electron-vibrational dynamics of photoexcited conjugated polyfluorenes shows that delocalized electronic excitations dominate the absorption, whereas chemical defects (if present) dramatically impact the emission by trapping the photogenerated exciton into a localized state and acting as guest emitters at recombination. These results offer theoretical insight into the effect of non-quenching defect sites in conjugated polymers and explain the origin of a controversial low energy emission band frequently observed in bulk polyfluorene samples.
Effects of metallic silver particles on the emission properties of [Ru(bpy)3]2+ by Ignacy Gryczynski; Joanna Malicka; Elisabeth Holder; Nicolas DiCesare; Joseph R. Lakowicz (409-414).
We examined the emission spectral properties of [Ru(bpy)3]2+ in a thin film of polyvinyl alcohol coated on quartz slides or on metallic silver particles. The relative intensities were several fold higher on the surface containing silver particles, and the decay times were several fold smaller. These results are consistent with an approximate 20-fold increase in the radiative decay rate of [Ru(bpy)3]2+ when near metallic silver particles. These results suggest the use of silver particles for increased detectability of the emission from transition metal–ligand complexes.
Spatially selective electrochemical deposition of composite films of metal and luminescent Si nanoparticles by A Smith; G Belomoin; M.H Nayfeh; Taysir Nayfeh (415-418).
We report on a procedure for selective deposition of Si nanoparticles using an electrochemical process. A conducting substrate is immersed in alcohol in which the particles are suspended. Biasing the substrate positively relative to a platinum electrode draws the Si particles to the substrate. Thin particle coatings on metal, foil, or silicon substrates are demonstrated. Fluorescent spectroscopy shows that the deposited particles retain the high luminescence efficiency and spectral distribution characteristic of the dispersed state. The process is used to deposit composite thin films of metal and Si nanoparticles. Dielectric masking allowed selective area deposition. These processes have implications for flat panel or flexible particle-based displays.
Contribution of hydrogen bonding to the slow diffusion of transient radicals by Koichi Okamoto; Yui Nogami; Toshihiro Tominaga; Masahide Terazima (419-422).
The translational diffusion of many transient radicals has been revealed to be different from that expected from the stable closed shell molecules. The origin of the slower diffusion of the radicals was investigated. In particular, participation of the hydrogen bonding to the diffusion process was considered from view points of excess friction and the solvent dependence.
Dynamical analysis of tRNAGln–GlnRS complex using normal mode calculation by Shugo Nakamura; Mitsunori Ikeguchi; Kentaro Shimizu (423-431).
We applied normal mode calculation in internal coordinates to a complex of glutamine transfer RNA (tRNAGln) and glutaminyl-tRNA synthetase (GlnRS). Calculated deviations of atoms agreed well with those obtained from X-ray data. The differences of motions corresponding to low mode frequencies between the free state and the complex state were analyzed. For GlnRS, many motions in the free state were conserved in the complex state, while the dynamics of tRNAGln was largely affected by the complex formation. Superimposed images of the conserved and non-conserved motions of tRNAGln clearly indicated the restricted direction of motions in the complex.
DNA interaction with single-walled carbon nanotubes: a SEIRA study by G.I Dovbeshko; O.P Repnytska; E.D Obraztsova; Y.V Shtogun (432-437).
Interaction of nucleic acids with graphite powder and SWCNT was studied by surface enhanced infrared absorption spectroscopy. The analysis of DNA-SWCNT complex vibrational modes shows that the numerous structural changes in DNA are connected to appearance of new sugar and bases conformations, changes in phosphate vibrations, which may be interpreted as A–B conformation transition and stabilisation of structure in some DNA fragments. A slight graphite influence on the DNA structure has been registered. The spectroscopic data could be explained by the model of DNA interaction with SWCNT based on wrapping of nucleic acid molecules around carbon nanotubes proposed by R. Smalley. A similar situation seems to occur in chromosome during DNA assembling by histones.
Experimental study of the second-order non-linear optical properties of tetrathia--helicene by Koen Clays; Kurt Wostyn; André Persoons; Stefano Maiorana; Antonio Papagni; Claude A. Daul; Valery Weber (438-442).
Femtosecond hyper-Rayleigh scattering (HRS) experiments as a function of amplitude modulation frequency have been performed on tetrathia--helicene. The apparent first hyperpolarizability β app(ω) is a decreasing function of increasing frequency ω, due to the two-photon fluorescence (2PF) contribution. We observe, however, for the first time, also a frequency-dependent HRS depolarization ratio ρ(ω). An accurate value for ρ is important, since it offers an indication for the symmetry of the chromophore (5, resp. 1.5, for dipoles, resp. octopoles, but also independent of frequency, since identical for HRS and 2PF). For helicoidal symmetry ρ(ω) is increasing for higher frequencies, in agreement with theory.
Rate coefficients for removal of CN(X 2 Σ +, ν=2) from selected rotational levels between N i=0 and 57 in collisions with N2 and C2H2 by Kevin M Hickson; Chester M Sadowski; Ian W.M Smith (443-450).
We report rate coefficients (k tot,i) for the total removal of CN(X 2 Σ +, ν=2, N i ) radicals from selected levels between N i = 0 and 57 in collisions with N2 and C2H2. Additionally, state-to-state rate coefficients (k i→f) have been measured for rotational energy transfer in collisions of CN(X 2 Σ +, ν=2, N i =0 and 1) with N2 and C2H2. In the case of CN+C2H2, by comparing the values of k tot,i with the sum of the state-to-state rate coefficients (Σf k i→f), we infer the rate constants for reaction (k reac,i) of CN(X 2 Σ +, ν=2, N i =0 and 1) with C2H2.
Synthesis and luminescence properties of SnO2 nanoparticles by Feng Gu; Shu Fen Wang; Chun Feng Song; Meng Kai Lü; Yong Xin Qi; Guang Jun Zhou; Dong Xu; Duo Rong Yuan (451-454).
Nanometer-scale SnO2 particles have been synthesized by a simple sol–gel method. The samples were characterized by X-ray diffraction, Fourier transform infrared (FTIR), UV–Vis absorption and photoluminescence spectroscopy. The as-prepared SnO2 nanoparticles appear to be single tetragonal crystalline phase and the diameter is about 2.6 nm. The origin of luminescence is assigned to the recombination of electrons in singly occupied oxygen vacancies with photoexcited holes in the valence band.
FSO+ and FSO2 + ions from ionised sulfur oxyfluorides: a computational investigation on the structure, stability, and thermochemistry by Paola Antoniotti; Paola Facchini; Felice Grandinetti (455-463).
Singlet and triplet F–S–O+, F–O–S+, F–S(O)–O+, and FO–SO+ isomers have been investigated at the Coupled Cluster, G2, and G3 theoretical levels. At the CCSD(T)/aug-cc-pVTZ//CCSD/cc-pVDZ, the F–S–O+ isomer 1S (1A′) and the F–S(O)–O+ isomer 3S (1A1) resulted the global minima on the singlet surfaces, more stable than the corresponding triplet by ≈64 and 47 kcal mol−1, respectively. The G2 and G3 estimates of the enthalpies of formation of the various singlet and triplet FSO+ and FSO2 + isomers allow to identify the species observed from the photon and electron ionization of the simplest sulfur oxyfluorides as the ions 1S and 3S.
A stochastic chiral amplification model by Dragan Todorović; Ivan Gutman; Mirko Radulović (464-468).
A stochastic version of Mason’s modification of the Frank chiral amplification model is examined. The initial state of the system is chosen to be strictly racemic. Nevertheless, the system always evolves to a monochiral terminal state. Two characteristic times are considered: the separation time t 0 – the moment after which the sign of the enantiomeric excess remains unchanged, and the parting time t p – the moment when the enantiomeric excess reaches 1% of its final value. Whereas t p depends (in average) linearly on the logarithm of the magnitude ξ of the fluctuations of the respective rate constants, the separation times are (in average) independent of ξ.
The composition and structures of covalent carbon nitride solids synthesized by solvothermal method by Qiang Lv; Chuan-Bao Cao; Jia-Tao Zhang; Chao Li; He-Sun Zhu (469-475).
Crystalline carbon nitrides have been synthesized by using a novel solvothermal method in which the reaction temperature and pressure were varied to determine the possible range for the formation of the crystalline phases. The chemical composition and states of elements were analyzed using X-ray photoelectron spectroscopy, electron energy-loss spectroscopy and Fourier transform infrared spectroscopy. X-ray diffraction (XRD) was used to characterize the powder structure. The maximum percentage of the single CN bonding in the powder was 55%, which is close to the theoretical value and the XRD pattern indicates the powder is mainly composed of α-C3N4 and β-C3N4.
Calculations of hydrogen-bond-transmitted indirect nuclear spin–spin couplings: a comparison of density-functional and ab initio methods by Magdalena Pecul; Joanna Sadlej; Trygve Helgaker (476-484).
Hydrogen-bond-transmitted indirect nuclear spin–spin coupling constants have been calculated by linear-response density-functional theory (DFT), coupled-cluster singles-and-doubles (CCSD) theory, and multiconfigurational self-consistent field (MCSCF) theory so as to benchmark the performance of DFT against the high-level ab initio methods. The systems under study are (NH3)2, (H2O)2, and (HF)2 and their charged counterparts N2H7 +, H5O2 +, and FHF−. In all cases, the 1h J(XH) coupling through the X–H⋯Y hydrogen bond changes sign in the transition from the neutral to charged complex. As for intramolecular coupling constants, description of 1h J(YH) and 2h J(XY) by DFT deteriorates with an increasing number of lone pairs on the coupled nuclei.
The ion–molecule reaction of O+ with N2 measured down to 23 K by J-L Le Garrec; S Carles; T Speck; J.B.A Mitchell; B.R Rowe; E.E Ferguson (485-488).
The rate constant of the O++N2 ion–molecule reaction has been measured from 225 down to 23 K with the CRESU technique. It has been found that the rate slightly increases when temperature decreases down to 23 K but remains two orders of magnitude below the Langevin rate. This indicates that the reaction does not occur via a long lived complex.
Intramolecular noncovalent force in cyclic amidines: nonbonded interaction between carbon atoms and heteroatoms by Xuhong Qian; Xiaoyong Xu; Zhibin Li; Antonio Frontera (489-496).
A set of four new cyclic amidines has been synthesized and characterized. A novel intramolecular noncovalent force between carbon atoms of the aromatic ring and heteroatoms of cyclic amidines has been demonstrated and established by X-ray structural analysis and ab initio calculation at B3LYP/6-31G* level. This new noncovalent force is presumably caused by an orbitalic overlap between the σ* or π* orbital of one aromatic carbon–carbon bond and one lone pair of electrons of the involved heteroatom. The generality of these interactions in organic compounds has been corroborated exploring the Cambridge Structural Database.
Surface-enhanced Raman of Z-vibration mode in single-walled and multi-walled carbon nanotube by Xu Zhang; Weide Zhang; Lei Liu; Z.X Shen (497-502).
Normal Raman scattering (NRS) and surface-enhanced Raman scattering (SERS) have been performed on single-walled and multi-walled carbon nanotubes to observe fine vibrational structures at the low- and intermediate-frequency regions. Following surface enhancement with silver particles, it is observed that the radial breathing mode, tangential mode, the overtone phonon peaks and coupling phonon peaks are suppressed. In contrast, the Z-breathing phonons, which correspond to vibration along the nanotube axis, and which are usually weak or non-existent in NRS, become enhanced in the SERS of both SWNTs and MWNTs.
Analysis of isotope effect of hydrogen-absorbing Pd ultra-fine particle by X-ray powder diffraction and first principle multi-component MO calculation by T Ishimoto; M Tachikawa; M Yamauchi; H Kitagawa; H Tokiwa; U Nagashima (503-507).
The isotope effect for the geometrical and electronical relaxations of the hydrogen/deuterium-absorbing ultra-fine particles of Pd has been investigated using an X-ray powder diffraction, which shows that the bond distances of Pd n H are longer about 0.005 Å than those of Pd n D. Also, the first principle multi-component molecular orbital (MC_MO) calculation, which takes account of the quantum effect of proton/deuteron, has been employed for the optimization of Pd n H− and Pd n D− (n=4,6). The H/D isotope effect of MC_MO calculation is good agreement with those of the X-ray powder diffraction and shows a little relaxation of the electronic charge densities.
Characterizing unpaired electrons from the one-particle density matrix by Martin Head-Gordon (508-511).
A new definition of the unpaired electrons in a molecule is proposed, which derives from the one-particle reduced density matrix. It yields lower estimates of the number of radical electrons than the widely discussed ‘distribution of effectively unpaired electrons’, with a maximum possible difference of a factor of two. Unlike the existing definition, the new definition cannot yield numbers of unpaired electrons higher than the total number of electrons, and also recovers the intuitively expected result for the dissociation of O2.
Sc2 dimer in IPR-violated C66 fullerene: a covalent bonded metallofullerene by Masaki Takata; E Nishibori; M Sakata; C R-Wang; H Shinohara (512-518).
The structure of an IPR-violated metallofullerene Sc2@C66 has been determined in the electron density level by the MEM/Rietveld method using synchrotron radiation powder data. The fundamental structure has been obtained by the Rietveld analysis. The cage structure of C66 has been unambiguously identified as that of Isomer No. 4348. The obtained charge density by the MEM analysis shows that the encapsulated two Sc atoms form the covalent bonded Sc2 dimer and that the charge density of dimer is overlapping with that of C66 cage, indicating the existence of a covalent bond character between Sc2 and the carbon cage.
A theoretical study of spin–orbit coupling in an Fe(II) spin-crossover complex. Mechanism of the LIESST effect by Masakazu Kondo; Kazunari Yoshizawa (519-523).
Spin–orbit coupling (SOC) in an Fe(II) spin-crossover system, [Fe(2-pic)3]Cl2·EtOH, where 2-pic denotes 2-picolylamine, is studied to understand the mechanism of light-induced excited spin state trapping (LIESST). The effects of SOC between the 1 T1( 1 T2, 5 E) states and the 3 T2 state are larger than those between the 1 T1( 1 T2, 5 E) states and the 3 T1 state. This suggests that the 3 T2 state can play a significant role in the LIESST and reverse-LIESST effects.
Optical nonlinear properties of metal cluster [PPh4][C* pWS3(CuBr)3(dppm)] by Xiao Rong Zhu; Rui Min Niu; Zhen Rong Sun; He Ping Zeng; Zu Geng Wang; Jian Ping Lang (524-528).
We report the nonlinear optical properties of one metal cluster [PPh4][C* pWS3(CuBr)3(dppm)] by picosecond and nanosecond laser pulses. The third-order nonlinear susceptibility χ (3) is measured by degenerate four-wave mixing, the nonlinear absorption by the Z-scan technique, and optical limiting response by the transmission technique. The experimental data are theoretically fitted, and the mechanism for the third-order optical nonlinearities and the optical limiting properties are discussed, and the absorption cross sections of the ground state and the excited state are evaluated by a rate equation model.
High-correlation methods for the calculations of the ground (X1Σ+) and first low-lying excited (A 3Σ+ and A 1Σ+) states dipole polarizabilities of NaLi by Mohammadou Mérawa; Didier Bégué; Alain Dargelos (529-537).
The dipole polarizability of the ground X 1 Σ + and excited A 3 Σ + , A 1 Σ + states of NaLi has been investigated at the ab initio level with effective core polarization potentials, by using the time-dependent gauge invariant method (TDGI). In the case of X 1 Σ + and A 3 Σ + states, alternative high-correlation methods have been applied for comparison. The accuracy of calculated polarizability components is supported by a careful check of the convergence with respect to the number of the spectroscopic states. The dependence of the polarizability on internuclear separation has also been computed. All the calculated electric properties of A 3 Σ + and A 1 Σ + excited states are new.
The Kohn–Sham treatment of anions via the localized Hartree–Fock method by Martin Weimer; Fabio Della Sala; Andreas Görling (538-547).
Kohn–Sham calculations of small anions with the localized Hartree–Fock (LHF) method, a recently developed effective exact exchange Kohn–Sham (KS) method, are presented. In contrast to conventional KS methods employing density-functionals from the local density or from generalized gradient approximations, the LHF approach yields bound anions, and thus, is found to be suitable for the treatment of anions. The superiority of the LHF method over conventional KS approaches originates in the fact that the former, in contrast to the latter, is free of Coulomb self-interaction. This is demonstrated by a discussion of the involved exchange and effective KS potentials.
Shannon’s entropy of proteomic 2D-gel maps by Danail Bonchev; Milan Randic (548-552).
2D gel proteomic maps are characterized by several invariants based on information theory. They are shown to discriminate well between maps of cells perturbed by different chemical agents. Potential applications to comparative proteomic studies are briefly discussed.
A computational study of the novel metastable compound HSKrH by Sean A.C. McDowell (553-556).
Ab initio calculations at the MP2/6-311++G(2d,2p) level of theory were performed on the rare-gas containing compound HSKrH. The calculations reveal that the molecule is metastable, with the dissociation energy to the lowest-energy fragmentation products Kr + H2S computed to be about −477 kJ mol−1. A possible transition state was also located for this fragmentation reaction and has a zero-point energy corrected barrier height of about 17 kJ mol−1, which indicates that this novel molecule may be prepared under suitable experimental conditions.
The infrared spectrum of NO2+: theory by Frederick R Bennett; Andrew D.J Critchley; George C King; Iain R McNab; Ralph C Shiell (557-562).
Although attempts to measure spectra of NO2+ using ion beam spectroscopy have been unsuccessful to date we show that the Newcastle ion-beam/infrared laser beam spectrometer should be capable of recording the spectrum calculated here. We report ab initio calculations of infrared spectra of NO2+ between levels of the A 2Π electronic state. The accuracy of our potential energy function is established by using it to synthesize a previously recorded TPEsCO spectrum of NO2+.
Massive enhancement of persistent spectral hole-burning in the R-lines of NaMgAl(oxalate)3 · 9H2O:Cr(III) by partial deuteration by Hans Riesen; Joseph L Hughes (563-568).
Partial deuteration of NaMgAl(oxalate)3 · 9H2O:Cr(III) (0.5%) increases the quantum efficiency for persistent spectral hole-burning in the R1-line by three orders of magnitude. A 50% deuterated crystal shows an impressive initial hole-burning efficiency of ≈0.1% and sharp anti-holes are observed in the range of ±15 GHz. A decrease of the quantum efficiency upon deuteration has often been reported in the literature and this has been rationalized on the basis of the lower tunnelling probability of the deuteron in the double well potential of hydrogen bonds. In contrast, the present findings of a sensational increase can be rationalized by a hole-burning mechanism based on 180° flip motions of the lattice water molecules around their pseudo C2 axes. Considering the spin-flip nature of the electronic excitation this is an extraordinary finding. The deuteration effect may be used to design high-efficiency hole-burning materials for optical storage at liquid nitrogen temperatures.
Reactions of HOBr + HCl + nH2O and HOBr + HBr + nH2O by Andreas F. Voegele; Christofer S. Tautermann; Thomas Loerting; Klaus R. Liedl (569-576).
The reactions of HOBr with HCl and HBr in the presence of n=0, 1, 2 and 3 water molecules are investigated by hybrid density functional theory methods in combination with canonical, variational transition state theory including tunneling corrections. Compared to the reactions of HOCl with HCl and HBr [J. Phys. Chem. A 106 (2002) 7850], we found that the barriers of the title reactions are significantly lower yielding much higher rate constants. Support of only two water molecules makes the reaction of HOBr with HBr barrierless. Under stratospheric conditions the reactions of HOBr with HBr are the most reactive ones.
Light emitting devices from blended films of ruthenium(II)bis(2,2′-bipyridine)(4,7-dimethyl-1,10-phenanthroline) complex with poly(N-vinylcarbazole) by Jihua Yang; Keith C Gordon (577-582).
The light emitting devices using ruthenium(II)bis(2,2′-bipyridine)(4,7-dimethyl-1,10-phenanthroline) [Ru(bpy)2DIM]2+ complex as emitter have been fabricated in two structures: indium–tin-oxide glass (ITO)/poly(N-vinylcarbazole) (PVK):[Ru(bpy)2DIM]2+/Al and ITO/PVK:[Ru(bpy)2DIM]2+/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)/tris-(8-hydroxyquinoline) aluminum (Alq3)/Al. In ITO/PVK:[Ru(bpy)2DIM]2+/Al, the emitter concentration influences both the turn on voltage and the emission wavelength. At 6 wt% [Ru(bpy)2DIM]2+ concentration, the device has a turn on voltage of 16 V and the emission peak at 600 nm. At 36 wt% [Ru(bpy)2DIM]2+ concentration, the device turn on voltage can be reduced to 3 V, with the emission peak at 620 nm. ITO/PVK:[Ru(bpy)2DIM]2+ (36 wt%)/BCP/Alq3)/Al obtains a quantum efficiency one order of magnitude higher than ITO/PVK:[Ru(bpy)2DIM]2+ (36 wt%)/Al.
Electronic properties of DNA binding site in transcription OmpR family: semiempirical molecular orbital calculations by Noriyuki Kurita; Yasuo Sengoku; Hideo Sekino (583-589).
To elucidate a common feature of OmpR family enhancing the transcription ability of RNA polymerase, we investigated structures and electronic properties of DNA binding sites of OmpR family by semiempirical molecular orbital (MO) calculations. The results clarify that the highest occupied MO is localized on the 2nd aspartic-acid existing near the DNA backbones for almost all members of OmpR family. Therefore, the 2nd aspartic-acid of DNA binding site is expected to be essential for the nonspecific interaction between OmpR and DNA backbones. The effect of amino-acid mutation on the structures and electronic properties of OmpR family was also investigated.
Solvothermal synthesis of porous tellurium nanotubes by Guodan Wei; Yuan Deng; Yuan-Hua Lin; Ce-Wen Nan (590-594).
Based on a solvothermal synthesis with N,N-dimethylformamide used as solvent and porous silicon as growth assistant, porous tellurium nanotubes with width of 100–400 nm and length up nearly to 40 μm were synthesized on a large scale. Of interest is that the porous tellurium nanotubes looks like lotus-roots with a few inner fibrilliform tubes parallel to each other. The formation mechanism of the tellurium nanotubes could be expressed as a dissolution–crystallization process. When the reaction duration was prolonged, single nanotubes with column morphology formed. Our results illustrate that the formation of tellurium nanotubes could be well controlled with appropriate template and reaction duration.
Surface modifications of carbon nanotube/polyacrylonitrile composite films by proton beams by Christophe Pirlot; Zineb Mekhalif; Antonio Fonseca; Janos B.Nagy; Guy Demortier; Joseph Delhalle (595-602).
Chemical and structural modifications induced by protons at the surface of polyacrylonitrile and carbon nanotube/polyacrylonitrile composite films are analysed by TEM, profilometry, IR and XPS. Changes induced in the film are related to the energy of incident particle and implanted dose. The irradiation of the composite films induces the emergence of the nanotubes outside of the polymer but with no increase of the surface roughness. Spectroscopic modifications in both films are globally similar, the most significant feature being a lower relative concentration of nitrogen with respect to carbon close to the surface.
Carbon nanotube growth enhanced by nitrogen incorporation by Tae-Young Kim; Kwang-Ryeol Lee; Kwang Yong Eun; Kyu-Hwan Oh (603-607).
It is well known that the growth of carbon nanotubes (CNTs) by chemical vapor deposition using a transition metal catalyst is greatly enhanced in a nitrogen environment. We show here that the enhanced growth is closely related to nitrogen incorporation into the CNT wall and cap during growth. This behavior is consistent with theoretical calculations of CN x thin films, showing that nitrogen incorporation to the graphitic basal plane reduces the elastic strain energy for curving the graphitic layer. Enhanced CNT growth by nitrogen incorporation is thus due to a decrease in the activation energies required for nucleation and growth of the tubular graphitic layer.