Influence of ro-vibrational and isotope effects on the dynamics of the C(3 P)+ OD(X 2Π) → CO(X 1 Σ+) + D(2 S) reaction

The C(³ P)+OD(X ²Π) reaction has been studied by means of quantum mechanical real wave packet (RWP) and quasiclassical trajectory (QCT) methodologies on the ground potential energy surface of Zanchet et al. [J. Phys. Chem. A 110, 12017 (2006)]. Initial state selected total reaction probabilities at J?=?0 total angular momentum have been calculated for a wide range of collision energies. Product state-resolved integral cross-sections at selected collision energies and excitation functions have been determined from the RWP calculations using the J-shifting approximation and from QCT calculations. State-specific and thermal rate coefficients have been calculated using both methodologies up to 500 K. The effect of reagent rotational excitation on the dynamics for the C(³ P)+OH(X ²Π) and C(³ P)+OD(X ²Π) reactions has been investigated and interesting discrepancies between the QCT and RWP results have been found. The RWP results are found to be in an overall good agreement with the corresponding QCT results, although the QCT integral cross-section and rate coefficients are slightly smaller than those obtained from the RWP calculations.     

Charge-exchange pigmy resonances of tin isotopes

Charge-exchange states, the so-called “pigmy” resonances, which are below the giant Gamow–Teller resonance, have been studied in the self-consistent theory of finite Fermi systems. Microscopic numerical calculations and semiclassical calculations are presented for nine tin isotopes with the mass numbers A =112, 114, 116, 117, 118, 119, 120, 122, and 124, for which experimental data exist. These data have been obtained in the Sn(³He,t)Sb charge-exchange reaction at the energy E(³He) = 200 MeV. The comparison of calculations with experimental data on the energies of charge-exchange resonances gives the standard deviation δE < 0.40 MeV for microscopic numerical calculations and δE < 0.55 MeV for calculations by semiclassical formulas, which are comparable with experimental errors. The strength function for the ¹¹⁸Sn isotope has been calculated. It has been shown that the calculated resonance energies are close to the experimental values; the calculated and experimental relations between heights of pygmy resonance peaks are also close to each other.     

Prior-form DWBA analysis of (3He,pd) elastic breakup at 90 MeV

Proton-deuteron coincident cross sections in ¹²C,⁵¹V,⁹⁰Zr(³He,pd) elastic breakup at 90 MeV have been calculated within the framework of the prior-form distorted-wave Born approximation (DWBA). Sufficient convergence of the calculations was obtained by including the pd relative angular momenta up to l = 4. The calculations reproduced the general trend of the coincident energy spectra and the angular correlation data, though deficiencies of the calculations were seen at some angles. The peripheral feature of the (³He, pd) elastic breakup is discussed from the angular momentum dependence of the transition amplitude.     

GaAs和AlAs光学声子形变势的第一性原理研究

本文以冻结声子近似模型,采用空球随原子球位移的冻结势近似的LMTO-ASA计算方案,研究了GaAs和AlAs布里渊区Λ轴的光学声子形变势的计算,得到Γ点和Λ轴光学声子形变势d₀,d₃₀,d₁₀(val)和d₁₀(comd)的第一性原理的计算结果。研究中着重从GaAs和AlAs的Λ轴光学声子形变势随k点的变化趋势,从光学声子形变势在Γ点附近满足的关系,以及从不同计算方法对d₀的计算结果与实验结果的比 关键词：     

FT‐Raman and FT‐IR spectral and quantum chemical studies on some flavonoid derivatives: Baicalein and Naringenin

In this study, the experimental and theoretical results on the molecular structures of some flavonoid derivatives (Baicalein and Naringenin) are presented. The FT‐IR and FT‐Raman spectra of the compounds have been recorded together for the first time between 4000–400 cm⁻¹ and 3500–5 cm⁻¹ regions, respectively. The molecular geometry and vibrational wavenumbers of the compounds have been also calculated in their ground states by using ab initio HF and DFT/B3LYP functional with 6‐31G(d,p) basis set used in calculations. The calculations were utilized to the C₁ symmetries of the molecules. All calculations were performed with Gaussian 98 software. The obtained vibrational wavenumbers and optimized geometric parameters were seen to be in good agreement with the experimental data. Scale factors have been used in order to compare how the calculated and experimental data are in agreement. Theoretical infrared intensities were also reported. Copyright © 2008 John Wiley & Sons, Ltd.     

Non-empirical versus empirical choices for overlapping-sphere radii ratios in SCF-Xα-SW calculations on ClO4 - and SO2

Two non-empirical schemes for establishing ratios of atomic sphere radii for Xα-SW calculations are proposed and compared with known methods of partitioning molecules into atomic fragments along paths of maximum change in electrostatic potential or charge density. In the initial Xα-SW molecular charge distribution, the radius of a sphere around each atom containing the atomic number of electrons is shown to be constant within a few per cent no matter what atomic charges are assumed in constructing the charge distribution. This contrasts with the radius of a sphere containing the number of electrons put in for the atom in calculating its atomic charge density, which shows a significant inverse variation with the assumed charge. Ionization energies for ClO₄ ^- and SO₂ are calculated using ratios of sphere radii established both from the atomic number sphere sizes and from Slater's empirical atomic radii. The results are compared with experiment and with HF-LCAO calculations. The Xα-SW calculations using atomic number radii ratios are in the best overall agreement with experiment.     

Hydrogen atom abstraction from Piperazine by hydroxyl radical: a theoretical investigation

Dual level of quantum mechanical calculations have been carried out for hydrogen abstraction from Piperazine [HN(CH₂CH₂)₂NH] initiated by OH radical. Geometry optimisation and frequency calculations of all species involved in the titled reaction have been performed at M06-2X/6-31+G(d,p) level of theory. For the accuracy in the thermochemistry and kinetics data, single-point energy calculations have been further carried out at coupled cluster CCSD(T) method along with 6-311G(d,p) basis set. An energy profile diagram for the reaction has been plotted along with pre-reactive and post-reactive complexes at entrance and exit channels. Intrinsic reaction coordinates (IRCs) calculations have been performed for identification of real transition states that connect it via reactant to product. Our result shows that the H-atom abstraction takes place from the C–H position of Piperazine. The rate constant is calculated using canonical transition state theory (CTST) is found to be 2.86 × 10^?10 cm³ molecule^?1 s^?1 which is in good agreement with the reported experimental rate constant (2.38 ± 0.28) × 10^?10 cm³ molecule^?1 s^?1 at 298 K. We have also reported rate constant for the temperature range 300–500 K. Using group-balance isodesmic reaction, the standard enthalpies of formation for Piperazine and product radicals generated by hydrogen abstraction are reported. The branching ratios for both reaction channel (i.e. H-abstraction from –CH₂ and –NH position of Piperazine) are found to be 93% and 7%, respectively. The calculated atmospheric life time of Piperazine is found to be 0.97 hour.     

Derivation of quantum yields for visible emission transitions of Sm in heavy metal tellurite glass

Under the pumping of violet lighting emitting diode, quantum yields for multichannel transition emissions have been determined in Sm³⁺-doped heavy metal tellurite glass for the first time. For the derivation, the necessary fluorescence spectra were measured and calibrated in an integrating sphere connected to a CCD detector with a 400 μm-core optical fiber. The spectral power distribution of the sample was derived from the measured spectra first, and then the quantum yields of the visible emissions of Sm³⁺ were calculated based on the distribution. The total quantum yield for four emission transitions of Sm³⁺ in visible region is 4.07%. Integrating sphere with a CCD detector is proven to be a reliable and reproducible method to characterize luminescence and laser materials.     

Calculation of absorption and resonance Raman cross sections of ClO2 in the gas‐phase and in solution: including Duschinsky effects

The time‐correlation function formalism has been used to calculate resonance Raman cross sections, excitation profiles, and electronic absorption spectra of the OClO molecule in the gas‐phase and in different solvents like cyclohexane, chloroform, and water. The multidimensional time domain integrals that arise in these calculations have been evaluated for the case in which an X²B₁ òA₁ electronic transition takes place between displaced‐distorted‐rotated harmonic potential energy surfaces. Ab initio calculations have been performed to provide the spectroscopic constants required for the evaluation of these integrals. The calculated absorption spectra and resonance Raman cross sections have been compared with the experimental results. Copyright © 2009 John Wiley & Sons, Ltd.     

Density functional theory calculation and vibrational spectral analysis of 4‐hydroxy‐3‐(3‐oxo‐1‐phenylbutyl)‐2H‐1‐benzopyran‐2‐one

The Fourier transform infrared (4000–400 cm⁻¹) and Fourier transform Raman (3500–500 cm⁻¹) spectra of 4‐hydroxy‐3‐(3‐oxo‐1‐phenylbutyl)‐2H‐1‐benzopyran‐2‐one (Warfarin) have been measured and calculated. The structure optimization has been made using density functional theory (DFT) calculations. Complete vibrational assignments of the observed spectra have been compared with theoretical wavenumbers. The wavenumber increasing in the methyl group shows the electronic hyperconjugation effect. The natural bond orbital (NBO) analysis reveals the hyperconjugation interaction and the intramolecular hydrogen bonding. The first‐order hyperpolarizability has been calculated. Copyright © 2009 John Wiley & Sons, Ltd.     

Solvent effects on adsorption of CO over CuCl(1 1 1) surface: A density functional theory study

DFT calculations have been performed to investigate the effect of dielectric responses of the solvent environment on the CO adsorption over CuCl(1 1 1) surface by using COSMO (conductor-like solvent model) model in Dmol³. Different dielectric constants, including vacuum, liquid paraffin, methylene chloride, methanol and water solution, are considered. The effects of solvent model on the structural parameters, adsorption energies and vibrational frequency of CO adsorption over CuCl(1 1 1) surface have been investigated. The calculation results suggest that solvent effects can improve the stability of CO adsorption and reduce the intensity of C-O bond, which might mean that solvent is in favor of C-O bond activation and improve the reaction activity of oxidative carbonylation in a slurry reactor.     

FT‐Raman,FT‐IR spectral and DFT studies on 6, 8‐dichloroflavone and 6, 8‐dibromoflavone

In this study, experimental and theoretical vibrational spectral results of the molecular structures of 6,8‐dichloroflavone (6,8‐dcf) and 6,8‐dibromoflavone (6,8‐dbf) are presented. The FT‐IR and FT‐Raman spectra of the compounds have been recorded together between 4000 and 400 cm⁻¹ and 3500–5 cm⁻¹ regions, respectively. The molecular geometry and vibrational wavenumbers of 6,8‐dcf and 6,8‐dbf in their ground state have been calculated by using DFT/B3LYP functional, with 6‐31 + + G(d,p) basis set used in calculations. All calculations were performed with Gaussian03 software. The obtained vibrational wavenumbers and optimized geometric parameters were seen to be in good agreement with the experimental data. Scale factors have been used in order to compare how the calculated and experimental data are in agreement. Theoretical infrared intensities are also reported. Copyright © 2009 John Wiley & Sons, Ltd.     

Total cross sections for some (α, n) and (α, p) reactions in medium-weight nuclei

Total cross sections have been measured for the ⁴⁵Sc(α, n), ⁴⁶Ti(α, n), ⁵⁰Cr(α, n), ⁵¹V(α, n), ⁵⁴Fe(α, n) and ⁵⁸Ni(α, p) reactions, and stellar reaction rates have been calculated from them. These have been compared to recent theoretical calculations which used compound nuclear theory. The calculated values are generally higher than the experimental values by factors ranging from 2 to 10.     

Computational studies on nonenzymatic pyroglutamylation mechanism of N-terminal glutamic acid residues in aqueous conditions*

Spontaneous cyclisation of glutamic acid (Glu) residues located at N-termini in peptides and proteins is called ‘pyroglutamylation’ and is assumed to be involved in several neurodegenerative diseases. Although it has long been believed that N-terminal Glu residues undergo pyroglutamylation enzymatically, it has recently been experimentally confirmed that nonenzymatic pyroglutamylation can proceed in some types of aqueous buffer. However, the detailed mechanism has not been proposed or investigated, and even whether some small-molecule catalysts are required for pyroglutamylation has not been clarified. Therefore, we investigated three types of pyroglutamylation mechanism of N-terminal Glu residues using quantum chemical calculations: in the absence of any catalysts, catalysed by one water molecule, and catalysed by two water molecules. All calculations were performed using N-terminal Glu residues capped with a methylamino group on the C-terminal as a model compound. Optimised energy minima and transition state geometries were obtained using the B3LYP density functional method. The pyroglutamylation mechanism is roughly divided into two steps: cyclisation and dehydration, and the calculated activation barrier was 108 and 107?kJ mol^?1 in the two- and three-water-assisted pathways, respectively. The results of computational analysis suggest that water molecules can act as catalysts for pyroglutamylation.

The calculated activation barrier of two-water-assisted pyroglutamylation was 108?kJ mol^?1, and the results of computational analysis indicate that water molecules can act as catalysts for pyroglutamylation.     

Excitation of He+ in a hollow cathode arc discharge

Population densities of the excited He(II) levels i=4 to i=10 in hollow cathode arc discharge have been determined and compared with those calculated from a collisional-radiative model. In the experiment the electron temperature was about 2x10⁵K and the electron density about 3x10¹⁹ m^-3. The observed population densities agree within 50% with those calculated by Drawin and Emard, but differ by a factor 4–6 from the ones found by McWhirter and Hearn. The results of the present experiment suggest that near the threshold energies the cross sections for electronic excitation of He⁺ levels from the He⁺ ground state are half those expected from the calculations of Burgess. We conclude that Drawin and Emard's calculations should preferably be employed for the determination of the electron density and the electron temperature from observed population densities.     

Interaction of Sulfadiazine with Model Water Soluble Proteins: A Combined Fluorescence Spectroscopic and Molecular Modeling Approach

The binding behavior of antibacterial drug sulfadiazine (SDZ) with water soluble globular proteins like bovine as well as human serum albumin (BSA and HSA, respectively) and lysozyme (LYS) was monitored by fluorescence titration and molecular docking calculations. The experimental data reveal that the quenching of the intrinsic protein fluorescence in presence of SDZ is due to the strong interaction in the drug binding site of the respective proteins. The Stern-Volmer plot shows positive deviation at higher quencher concentration for all the proteins and was explained in terms of a sphere of action model. The calculated fluorophore-quencher distances vary within 4?~?11 Å in different cases. Fluorescence experiments at different temperature indicate thermodynamically favorable binding of SDZ with the proteins with apparently strong association constant (~10⁴–10⁵ M^?1) and negative free energy of interaction within the range of ?26.0?~??36.8 kJ mol^?1. The experimental findings are in good agreement with the respective parameters obtained from best energy ranked molecular docking calculation results of SDZ with all the three proteins.     

Two-dimensional Penning ionization electron spectroscopic study on outer characteristics of molecules

Collision-energy/electron-energy-resolved two-dimensional Penning ionization electron spectroscopy (2D-PIES) has been used to study outer characteristics of molecules. Anisotropic potential energy surfaces for collisional ionization of molecules with a metastable helium atom He*(2³S) have been determined starting from ab initio model potentials via optimization based on trajectory calculations. Since ionization widths in the theoretical model of Penning ionization are functionals of target molecular orbitals, outer electron distributions of molecular orbitals can be determined via optimization procedures of calculated ionization cross-sections by trajectory calculations with respect to observed 2D-PIES data.     

Quasiclassical trajectory calculations of the isotopic effect on cross-sections of reactions O(1D) + HCl (DCl,TCl)

The paper reports on a quasiclassical trajectory (QCT) study of the O(¹D) + HCl (DCl, TCl) reactions, with emphasis on the isotopic effect on cross-sections and branching ratio. The calculations were performed on the ground 1 ¹ A' potential energy surface (PES). The cross-sections and branching ratios of the O(¹D) + HCl (DCl, TCl) reaction have been calculated at the collision energies (E _col) of 3–15 kcal/mol. Obvious differences have been found in the energy dependences of the reaction cross-sections and branching ratios among these isotopic reactions.     

Sodium affinity of caffeine and adenine: the effect of microsolvation and electrostatic field of solvent on the sodium affinity

The sodium affinity (SA) of caffeine (CAF), adenine (AD) and their microsolvated clusters containing one X molecule (CAF-X and AD-X; X = H₂O, NH₃, H₂S and HF) has been calculated in the gas phase and water, separately. The density functional theory (DFT) employing CAM-B3LYP functional has been used for all of the calculations in this work. The solvent was modelled by the polarised continuum model (PCM) which considers the electrostatic field of solvent on solute. The calculated SA of [CAF-X] and [AD-X] was higher than that of CAF and AD in the gas phase, respectively, which showed that the microsolvation of molecules in the gas phase could be used for changing the tendency of molecules for binding to Na⁺. Also, it was observed that the electrostatic effect of solvent decreases the SA of the species compared to the gas phase, considerably. The symmetry adapted perturbation theory (SAPT) calculations were also used to interpret the change in the SA of CAF and AD due to the clustering with one X molecule in the gas phase. In addition, there is a detailed study on the position of Na⁺ relative to AD and CAF structures in different conditions including gas phase, microsolvation and electrostatic field of solvent in this work.