Chemical Physics Letters (v.373, #1-2)

Density functional theory and ab initio direct dynamics study on the reaction of BCl3+H→BCl2+HCl by Shaowen Zhang; Yue Zhang; Chao Yang Wang; Qian Shu Li (1-7).
We present a direct ab initio dynamics study of thermal rate constants of the abstraction reaction of BCl3+H→BCl2+HCl. The geometries of all the stationary points are optimized at a variety of DFT and QCISD methods with both 6-31+G(d,p) and 6-311+G(d,p) basis sets. The energies are refined at the MC-QCISD, G3, G3MP2 and QCISD(T)/6-311+G(2df,2pd) level of theory. The rate constants are evaluated using the conventional transition-state theory, canonical variational transition-state theory and canonical variational transition-state theory with small curvature tunneling correction.

Ab initio and model investigation of acetylene clustering around hydrogen cyanide by William P Schroeder; Kimberly Chenoweth; Clifford E Dykstra (8-14).
Ab initio calculations have been performed to determine the structures and interaction energetics of (HCCH)2–HCN and certain related clusters. The clusters have arrangements of each HCN–HCCH pair being essentially either T-shaped, with the HCN as a proton donor, or linear, with the acetylene as the proton donor to the nitrogen end of HCN. Three-body energetic features are small as are the polarization energy effects. A model potential has been applied to these and larger clusters. Though strongly polar, substitution of one HCN for acetylene in a pure cluster yields small structural differences.

We have performed density functional theory calculations to investigate SO2 adsorption on both ideal and defective TiO2(1 1 0) surfaces. In agreement with experiments, we identify SO2-, SO3- and SO4-like adsorption complexes. We also find that adsorption on the defective surface leads to very strong bonding between the molecule and the surface. More importantly, we show that upon adsorption on the defective surface the S hybridization changes from the sp2 in the isolated molecule to the sp3 type. We demonstrate that the change is responsible for the formation of stable SO4-like species at high temperature.

ZnO nanoparticles prepared by thermal decomposition of β-cyclodextrin coated zinc acetate by Yang Yang; Xuefei Li; Jianbin Chen; Huilan Chen; Ximao Bao (22-27).
Uniform ZnO nanoparticles have been prepared via a convenient thermal decomposition approach, in which β-cyclodextrin (β-CD) is selected to coat the precursor of zinc acetate. The decomposition process of this system is investigated by thermogravimetric and differential thermal analysis (TG–DTA). TEM or AFM studies reveal that ZnO nanoparticles and the corresponding film doped on the silicon substrate by this method present weak agglomeration and regular size distribution. The possible formation mechanism of ZnO nanoparticles under the effects of β-CD coating is also discussed.

Single crystalline In2O3 nanowires (InONWs) have been synthesized by carbothermal reduction reaction between indium oxide and active carbons at 980 °C in flowing nitrogen atmosphere. Transmission electron microscopy (TEM) image shows the formation of the nanowires at a diameter of about 20–200 nm and a length of up to hundreds of micrometers. The nanowires can emit stable and high brightness blue light at 416 and 435 nm under excitation at 260 nm. The growth process of the nanowires may be explained by vapor–solid mechanism.

Theoretical study on the abstract reaction of O( 3 P ) with CHFCl2 by Shaokun Wang; Qingzhu Zhang; Yueshu Gu (33-38).
The reaction of O( 3 P ) with CHFCl2 has been studied using ab initio molecular orbital theory. Two nearly degenerate transition states of 3 A″ and 3 A symmetries were located for this reaction. The kinetic nature is obtained using canonical variational transition state theory with small-curvature tunneling correction method. The calculated rate constants exhibit typical non-Arrhenius behavior, a three-parameter rate-temperature formula is fitted as follows: k(T)=2.627×10−22T3.55 exp(−2525.56/T)  cm 3   molecule −1   s −1 over a wide temperature range of 200–3000 K. The calculated results match well with the experimental values.

Synthesis and characterization of n-octadecayl mercaptan-protected palladium nanoparticles by C.M Shen; Y.K Su; H.T Yang; T.Z Yang; H.J Gao (39-45).
Long-chain n-octadecayl mercaptan (C18H37SH)-passivated palladium nanoparticles are synthesized and characterized. The palladium nanoparticles are successfully capped by n-octadecayl mercaptan. These palladium nanoparticles have the same face-centered cubic crystalline structure as Pd in the bulk phase. The size of the capped palladium nanoparticles varies in the range of 1.3–5.5 nm for various reaction conditions. These results show that the long-chain n-octadecayl mercaptan-capped palladium nanoparticles are more stable than alkanethiolate-capped Pd nanoparticles with a shorter chain.

Density functional theory is used to describe the reaction profile for methane activation on the MoO2/HZSM-5 active center. The physisorbed state of methane on the Mo center and the transition state structure of C–H bond dissociation were obtained, and the barrier energy was calculated. The local and nonlocal density functional activation barriers were 91 and 158 kJ/mol, respectively. In the dissociative state the methyl moiety was connected to molybdenum, and the dissociated hydrogen combined with the extraframework oxygen to form a hydroxyl group. The mechanism of methane activation on the MoO2/HZSM-5 active center is discussed.

Characterisation of carbon nano-onions using Raman spectroscopy by D Roy; Manish Chhowalla; H Wang; N Sano; I Alexandrou; T.W Clyne; G.A.J Amaratunga (52-56).
Characteristics of the Raman spectrum from carbon onions have been identified in terms of the position of the G peak and appearance of the transverse optic phonon peaks. Five new peaks were observed in the low wavenumber region, at about 1100, 861, 700, 450 and 250 cm−1. The origins of these peaks are discussed in terms of the phonon density of states (PDOS) and phonon dispersion curves of graphite. The curvature of the graphene planes is invoked to explain the relaxation of the Raman selection rules and the appearance of the new peaks. The Raman spectrum of carbon onions is compared with that of highly oriented pyrolytic graphite (HOPG). The strain of graphene planes due to curvature has been estimated analytically and is used to account for the downward shift of the G peak.

The phase transformation between cubic boron nitride (c-BN) and hexagonal boron nitride (h-BN) from the c-BN nanocrystals synthesis by pulsed laser induced liquid–solid interfacial reaction (PLIIR) was studied by calculating the probability of phase transition of the h-BN structure over a potential barrier in boron nitride equilibrium phase diagram. Consequently, we found that the probability of phase transition from h-BN to c-BN goes up to 10−5–10−4 in the pressure–temperature region of 5–6 GPa and 2500–3500 K created by PLIIR. Furthermore, the probability distribution of the phase transition from h-BN to c-BN was obtained in the corresponding pressure–temperature region, and the dependence of phase transition probability on temperature was found to be in agreement with the Arrhenius rule.

The bifurcation analyses of the internal rotation processes of two different series of monorotor molecules along the reduced reaction coordinate are investigated in this Letter. Our topological analyses indicate that the internal rotation processes are characterized by the properties of critical points. Furthermore, when the energy functions are represented as the third-order generic polynomial of the reduced reaction coordinate, the processes are isomorphic to the elementary fold catastrophe.

Singlet state exciplex formation of phenazine with some aromatic amines by Sharmistha Dutta Choudhury; Samita Basu (67-71).
Exciplex formation of phenazine with some aromatic amines i.e., N,N-diethylaniline, N,N-dimethylaniline and 4,4-bis(dimethylamino)diphenylmethane has been studied by steady state fluorescence measurements. Some interesting features of the exciplex were observed which have been attributed to the fast intersystem crossing of the phenazine molecule.

The substituent effect on geometries, energies, frequencies and charge distributions of the various DNA base pair derivatives was evaluated using density functional theory at B3LYP/6-31G* level. The results indicate that the fluorine-substituted cytosine has great influence over the stabilization energy of the various C:G derivatives while the nitro-substituted thymine affects the stabilization energies most deeply among all the A:T derivatives. The N–H stretching vibrational frequency is red shifted and the shift is almost linear correlated with the N–H bond length elongation. There is no direct relationship between the charge distribution and the stabilization energy.

We have performed a series of molecular dynamics simulations of water containing either a methanol or an acetonitrile molecule to investigate the pressure dependence of various dynamical properties of these hydrogen bonding solutes in aqueous medium under ambient and supercooled conditions. It is found that the tracer diffusion and orientational relaxation of both the solutes in supercooled water and also the orientational relaxation of methanol in ambient water show anomalous behaviour with application of pressure. However, the extent of anomaly is quite different for the two solutes which is attributed to their varying hydrogen bond properties in aqueous medium.

The dynamical properties of water molecules at the liquid–vapour interfaces of aqueous NaCl solutions are studied by means of molecular dynamics simulations. The diffusion coefficients and the orientational relaxation times of the interfacial molecules of pure water and also the effects of ion concentration on these interfacial dynamical properties of aqueous solutions are investigated and the results are compared with those of the corresponding bulk phases. The inhomogeneous density, anisotropic orientational profiles and the surface tension are also calculated in order to characterize the location, width and the thermodynamic aspects of the interfaces and to explore their effects on the dynamical properties.

Zinc tetraphenylporphyrin forms J-aggregates, consisting mainly of dimers at moderate concentrations, in freshly-prepared dry acetonitrile solution at room temperature. The kinetics of disaggregation of these dimers may be followed by monitoring their absorption and emission spectra and their fluorescence lifetimes as a function of time and temperature following dilution. The activation energy of the disaggregation process is 20.0 kJ mol−1.

High-resolution cavity enhanced absorption spectroscopy (CEAS) using a fast power-modulated laser with a phase-sensitive detection scheme has been adopted. A detailed investigation into the effects of laser chopping frequency and cavity modulation frequency (via a piezoelectric translator) on the sensitivity will be presented. The observed detection sensitivity has been improved by more than an order of magnitude after the implementation of phase sensitive detection. The observed single-scan sensitivity of the present setup is about 4.4 ppm Hz−1/2 in fractional absorption using cavity mirrors with moderate reflectivity of ∼0.9997 and a ringdown cavity cell of 175 cm in length.

Electron field emission from soluble carbon nanotube films treated by hydrogen plasma by Ke Yu; Ziqiang Zhu; Min Xu; Qiong Li; Wei Lu (109-114).
Large-scaled and homogeneous multi-wall carbon nanotube (MWNT) films have been fabricated using the soluble octadecylamine (ODA) modified multi-wall carbon nanotubes at room temperature by a spin-coating method. The characterization, by means of electron microscopy and micro-Raman spectroscopy, shows that the surfaces of MWNTs-ODA with hydrogen plasma treatment are covered by the carbon nanoparticles. The field emission test indicates that the treated MWNTs-ODA film has low turn-on emission field of 0.5 V/μm at 0.1 μA/cm2 of current density, high-emission luminescent site density of about 104/cm2.

Time dependent density functional theory of core electrons excitations by M Stener; G Fronzoni; M de Simone (115-123).
The Time Dependent Density Functional Theory (TD-DFT) method implemented in the ADF program has been extended to treat core electrons excitations. The scheme consists to reduce the complete one-electron excited configurations space to the subspace where only the core electrons are excited. The scheme has been applied to the Ti 1s, Ti 2p and Cl 2p core excitations of TiCl4, employing different basis sets and exchange correlation potentials. The comparison with the experimental data is good, especially for the Ti 2p shell which cannot be described even qualitatively by the too simple Kohn–Sham method. Also the Cl 2p shell, dominated by Rydberg features, is properly described. The method is computationally economic, and can be applied to larger and less symmetric systems. Further extensions to the relativistic case, with explicit spin–orbit treatment, are suggested to improve the description of spin–orbit splitting and intensity redistributions.

Reaction of Cl with N3: a CAS study by Bo-Zhen Chen; Ming-Bao Huang (124-130).
The CAS methods were used for exploring mechanisms of the Cl + N3(X 2 Π ) → NCl( 1 Δ ) + N2 (i) and Cl + N3(X 2 Π ) → NCl(X 3 Σ ) + N2 (ii) reactions. The CASSCF/cc- pVTZ path calculations indicate that channel (i) occurs in the 1A potential energy surface (PES) and there exists an intermediate (IM(1A)) followed by a transition state along the reaction path and that channel (ii) occurs in the 3A′′ PES and it has a single step with a transition state. The CASPT2/cc-pVTZ energetic results indicate that channel (i) is feasible while channel (ii) is unfeasible. Preliminary exploration for the 1A3A′′ PES crossing at the CASSCF/cc-pVTZ level implies that the crossing may not cause predissociation of IM(1A) into the ground state product (NCl ( 3 Σ ) + N2).

All-electron CCSD(T), QCISD(T) and MP4(SDQ) calculations including relativistic effects via the use of the IORAmm Hamiltonian have been performed for PdCO. The optimized molecular geometry is in nice agreement with the recently obtained experimental data. The Pd–CO bond dissociation energy is estimated to be 38.8 kcal/mol. The vibrational spectrum of PdCO is calculated and a reassessment of the experimental datum for the frequency of bending mode is suggested.

Through the unique white-beam synchrotron radiation topography (WBSRT) method with several Al foils covering the sample, we have investigated in situ phase transition behavior in unpoled relaxor ferroelectric 0.92Pb (Zn1/3Nb2/3)O3–0.08PbTiO3 (PZN–8%PT) crystals and found it was anomalous to that reported previously. According to the ferroelectric domain growth behavior on heating and cooling, it was demonstrated that the unpoled PZN–8%PT crystal undergone three phase transitions, i.e., the rhombohedral-orthorhombic (R–O) phase transition at 75 °C, the rhombohedral-monoclinic or orthorhombic–tetragonal (R–M/O–T) phase transition at 132 °C, and the monoclinic or tetragonal–cubic (M–C/T–C) phase transition at 262 °C. DSC analysis revealed that the R–O phase transition and the M–C/T–C transition was of the first-order, while the R–M/O–T one belonged to the second-order type.

We investigated the structures induced in polysilane and polysilane coated thermoplastic bis-phenol A type epoxy (Epoxy) and poly(methyl methacrylate) (PMMA) films by irradiation of near-infrared (NIR) femto-second laser pulse. Long stripe-shaped structures with approximately 200–400 μm length was induced in polysilane bulk. Thin polysilane layer coated Epoxy and PMMA films showed photo-sensitive effect on the formation of stripe-shaped structures in PMMA and Epoxy, whereas no structures were induced in uncoated PMMA and Epoxy films. An ensemble of stripe-shaped structures worked as a diffraction grating. This photo-sensitive effect has potential application to grating structures in optical polymeric fiber (OPF).

In this Letter, the general and rigorous approach for deriving adiabatically constrained kinetic energy operators of Gatti et al. is reformulated and simplified. Emphasis is placed on weakly bound systems such as van der Waals polymers, molecules bound to a surface or located inside a rare gas matrix since an adiabatic approximation might turn out to be very relevant for them. This allows us to recast the flexible adiabatic monomer formulation into that for the rigid case.

Charge-transfer transitions in triarylamine mixed-valence systems: the effect of temperature by V Coropceanu; C Lambert; G Nöll; J.L Brédas (153-160).
The temperature dependence of inter-valence charger-transfer transitions has been investigated for three triarylamine-based mixed-valence systems: (bis-{4-[N,N-di(4-methoxyphenyl)amino]-phenyl}butadiyne, 1 + ), (4,4-bis[N,N-di(4-methoxyphenyl)amino] biphenyl, 2 + ), and (N,N,N ,N -tetraphenyl-1,4-phenylenediamine, 3 + ). Although the band shape of 1 +3 + changes with temperature, neither the position of the transition maximum nor the integral intensity are significantly affected by temperature. The shape of the absorption bands is analyzed in the framework of a dynamic vibronic model.

Product desorption dynamics in explosive NO + CO reaction on Pt(1 0 0) by Yuichi Ohno; Phupaichitkun Sarawut; Hideyuki Horino; Ivan Kobal; Atsuko Hiratsuka; Tatsuo Matsushima (161-166).
The angular and velocity distributions of desorbing products N2 and CO2 were studied in an explosive NO(a) + CO(a) reaction on Pt(1 0 0) by means of angle-resolved thermal desorption combined with cross-correlation time-of-flight techniques. The desorption peak of CO2 and N2 appeared in a narrow temperature range at 360–400 K. Desorption of both products sharply collimated along the surface normal. The velocity distribution of desorbing N2 showed three components with the translational temperatures of about 3500, 2000, and 600–800 K, whereas that of CO2 yielded only a single component of 1200 K.

Using density-functional theory and ZINDO methods, we carry out a comparative study of the two-photon absorption (TPA) properties of a new octupolar compound – truxenone derivative and relative molecules. The results indicate that the octupolar compounds have significantly increased the TPA cross-section of molecules and at the same time maintain the high transparency. The TPA cross-section value increases as the electron-accepting ability of the core in octupolar chromophores increases. It is notable that the truxenone derivative has more predominant TPA properties than the conventional octupolar compounds and so worth investigating further.

Volume and enthalpy changes of peroxodiphosphate dissociation by Mariana Mesaros; Gabriel M Bilmes; Janina A Rosso; Mónica C Gonzalez; Daniel O Mártire (176-181).
Photoacoustic measurements as a function of temperature in the range (294.1–308.2) K were used to determine the enthalpy and volume changes for the photoinduced dissociation at 266 nm of peroxodiphosphate ions in water. The analysis of the data, which considered the temperature dependence of the photodissociation quantum yield and of the thermoelastic parameters of the medium, yielded enthalpy and volume changes of (77±18)  kJ   mol −1 and (12±1)  ml   mol −1 , respectively. These values are compared with those reported for other systems.

Ab initio energy evaluations on the Z and E rotamers, as well as on the rotational transition states connecting them, were carried out for methyl formate and trifluoromethyl formate. The estimates for the energy differences at the basis set limit suggested that the Z/E energy difference and the rotational barrier height are both significantly smaller for trifluoromethyl formate than for methyl formate. Our best estimate for the enthalpy difference at 298 K between the Z and E rotamers for methyl formate is 5.21 kcal/mol, which is slightly larger than the upper edge of uncertainty of previously reported experimental value.

The photophysical and photocatalytic properties of BaCr2O4 synthesized with normal spinel-type crystal structure were studied. It was found that H2 could be photocatalytically evolved from the aqueous CH3OH solution suspended with Pt(0.2 wt%)/BaCr2O4 powder under irradiation of both ultraviolet (UV) and visible lights. The wavelength dependence of H2 evolution under visible light irradiation showed a maximum activity for λ>540  nm . A possible electronic band structure and corresponding photoexcitation modes of BaCr2O4 under irradiation of UV and visible lights were proposed in regard to the complicated photophysical and photocatalytic properties.

The geometric and electronic structures of porphyrin and a series of carbaporphyrins have been theoretically studied using the time-dependent density functional theory (TDDFT). The two-photon absorption cross sections (TPACS) of these molecules are computed using the ZINDO-SOS formula. The calculated results indicate that when the N atom is substituted by the C atom, the molecular center is enlarged and the absorptions are red-shifted and that porphyrin, carbaporphyrin, opp-dicarbaporphyrin and adj-dicarbaporphyrin show TPACS in small absorption area, while tetracarbaporphyrin has fairly large two-photon absorptions in comparatively larger area, which may lead it to many practical applications.

Structural origin of the enhanced electro-optic response of dendrimeric systems by Yuriy V Pereverzev; Oleg V Prezhdo; Larry R Dalton (207-212).
The structural origin of the enhancement of the electro-optic (EO) activity of a dendrimeric material, relative to the traditional guest–host polymer, is established within an analytic model. Chemical bonding between the chromophore fragments in the dendrimer suppresses the antiferroelectric correlation of the chromophore dipoles and assists in the macroscopic ordering of the dipoles by an applied field. The developed analytic model quantitatively agrees with the experimental data both for the increased EO coefficient of the cross-linkable dendrimer, and the decreased EO coefficient of the non-cross-linkable dendrimer. The model facilitates optimization of the structural and molecular properties of dendrimers and chromophore fragments in order to achieve materials with better EO response.

Theoretical study of hydrolysis reactions of tetravalent thorium ion by Yasuharu Okamoto; Yuji Mochizuki; Satoru Tsushima (213-217).
The hydrolysis reaction of the tetravalent thorium (Th4+) ion was investigated by ab initio theoretical calculations on hydration complex models. The transition state structure was optimized, and the intrinsic reaction coordinate was traced. The results showed that the hydrolysis is highly exothermic and the transition state is close to the reactant. Reaction dependency upon the number of non-reactive water molecules was examined.

Electron affinity of positronium embedded in Debye plasma by B Saha; T.K Mukherjee; P.K Mukherjee (218-222).
The effect of environment like that of a plasma on the ground state energy of positronium minus ion (Ps) has been estimated variationally using multi-term correlated basis sets. Debye model has been applied to include the plasma screening effect in the interaction energy between two charge particles. The electron affinity of positronium is estimated for different Debye screening parameters and is found to decrease monotonically with increasing screening.

Photoluminescence of sol–gel derived ZnTiO3:Ni2+ nanocrystals by Shu Fen Wang; Feng Gu; Meng Kai Lü; Chun Feng Song; Dong Xu; Duo Rong Yuan; Su Wen Liu (223-227).
Cubic ZnTiO3 nanocrystal doped with Ni2+ ion has been synthesized by sol–gel method at a lower temperature (600 °C). The crystallinity of the doped sample was characterized by the X-ray diffraction (XRD) patterns and the infrared spectra (IR). The photoluminescence (PL) spectra of the sample measured at different excitation wavelength reveal a novel luminescent phenomenon in blue, green and red region, which can be attributed to the 3T1(3P)–3A2(3F), 1T2(1D)–3A2(3F) and 1T2(1D)–3T2(3F) transitions of Ni2+ ion, respectively. The position of the emission peak does not change greatly with the excitation wavelength. However, the luminescent intensities vary with changing the concentration of Ni2+ ion in ZnTiO3.