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191.
Helge Johansen 《Theoretical chemistry accounts》1974,32(3):273-278
Ab initio SCF LCAO MO calculations have been performed for the ground states of the perchlorate, sulphate and phosphate ions. The basis sets used consisted of contracted gaussian-type orbitals having 12s, 10p and 2d-type primitive functions on the central atoms and 10s and 6p-type functions on the oxygens. The results are thought to be nearly at the Hartree-Fock limit. 相似文献
192.
Odd Gropen Ragnar Johansen Arne Haaland Oddvar Stokkeland 《Journal of organometallic chemistry》1975,92(2):147-156
Ab initio molecular orbital calculations have been carried out on H3AlOH2, (H2AlOH)2, and some related species, and the charge distribution and bonding are discussed on the basis of population analyses. It is found that the equilibrium conformation around the O atom in H3AlOH and (H2AlOH)2 is intermediate between trigonal and tetrahedral. The energy minima are, however, very shallow. In H3AlOH2 the angle between the Al-O bond and the H2O plane is 27°, in (H2AlOH)2 the angle between the two O-H bonds and the Al2O2 ring plane is 25°. The energy of a planar conformation of H3AlOH2 is 0.19 kcal mol-1, the energy of a planar conformation of (H2AlOH)2 0.35 kcal mol-1 above the equilibrium conformation. There is no indication for the formation of dative pπ-dπ bonds between O and Al in the two molecules. It is suggested that the conformation adopted by analogous alkyl derivatives, R3AlOR'2 and (R2AlOR')n is determined by intramolecular van der Waals repulsion. 相似文献
193.
The photochemistry of the system water-tris(2,2′-bipyridine)ruthenium(II) dication—9-anthracenecarboxylate anion—methylviologen—ethylenediaminetetraacetic acid—platinum has been studied. Efficient triplet energy transfer from the excited ruthenium complex to the anthracene derivative leads to the formation of hydrogen in quantum yields up to 0.85. 相似文献
194.
195.
Axel Finke Adam M. Johansen Dario Spanò 《Annals of the Institute of Statistical Mathematics》2014,66(3):577-609
We develop particle Gibbs samplers for static-parameter estimation in discretely observed piecewise deterministic process (PDPs). PDPs are stochastic processes that jump randomly at a countable number of stopping times but otherwise evolve deterministically in continuous time. A sequential Monte Carlo (SMC) sampler for filtering in PDPs has recently been proposed. We first provide new insight into the consequences of an approximation inherent within that algorithm. We then derive a new representation of the algorithm. It simplifies ensuring that the importance weights exist and also allows the use of variance-reduction techniques known as backward and ancestor sampling. Finally, we propose a novel Gibbs step that improves mixing in particle Gibbs samplers whose SMC algorithms make use of large collections of auxiliary variables, such as many instances of SMC samplers. We provide a comparison between the two particle Gibbs samplers for PDPs developed in this paper. Simulation results indicate that they can outperform reversible-jump MCMC approaches. 相似文献
196.
The molecular and conformational structures of 3-chloropropanoyl chloride (CH(2)Cl-CH(2)-C(=O)Cl) have been studied by using gas-phase electron diffraction (GED) data obtained at 22 degrees C (295 K) and ab initio molecular orbital (MO) and density functional theory (DFT) calculations up to the levels of MP4(SDQ) and B3LYP using larger basis sets. Normal coordinate calculations (NCA) taking into account nonlinear vibrational effects were also used in the analyses. The title compound may have up to four low-energy conformers in the gas phase, labeled according to the position of each of the two chlorine atoms in relation to the CCC propanoyl backbone, labeling the carbonyl chlorine torsion angle first: AA, AG, GG, and GA; where A is anti (ideal C-C-C-Cl torsion angle of approximately 180 degrees) and G is gauche (ideal C-C-C-Cl torsion angle of approximately 60 degrees). It has been judged from the experimental GED data and the theoretical calculations, as well as from previously published infrared (IR) studies on the molecule in both the liquid phase and in argon-trapped matrices at 10 K, that the gas phase consists of a mixture of at least three conformers: AA (most stable), AG, and GG, with the possibility of a smaller contribution (<10%) from the higher-energy GA form. The GA conformer cannot be ruled out by the GED experimental data. Relevant structural parameter values obtained from the GED least-squares refinements, with calculated ab initio MO MP2/6-31+G(2d,p) values used as constraints, were as follows (AA values with estimated 2sigma uncertainties): Bond lengths (r(h1)): r(C-C(=O)) = 1.505(4) A, r(C-CH(2)Cl) = 1.520(4) A, r(C=O) = 1.197(4) A, r(C(=O)-Cl) = 1.789(3) A, and r(C-Cl) = 1.782(3) A. Bond angles (angle(h1)): angle CCC = 111.5(11) degrees , angle CCO = 127.0(5) degrees, angle CC(O)Cl = 112.5(3) degrees, and angle CCCl = 110.3(3) degrees. Torsion angles (phi(C-C) = phi(ClCCC)): for AA, phi(1)(C-C(O)) = phi(2)(C-CH(2)Cl) = 180 degrees (assumed for true C(s) symmetry); for AG, phi(1)(C-C(O)) = -140(5) degrees, phi(2)(C-CH(2)Cl) = 76(13) degrees; for GG, phi(1)(C-C(O)) = 46(8) degrees, phi(2)(C-CH(2)Cl) = 77(14) degrees; for GA, phi(1)(C-C(O)) = 67.9 degrees (assumed), phi(2)(C-CH(2)Cl) = 177.8 degrees (assumed). The non-AA conformers all have chiral C(1) symmetry with twice the statistical weight (multiplicity) of C(s). The MP2/6-31+G(2d,p) calculated composition (%) based on the zero-point energy (ZPE) corrected energy differences, and the statistical weights for conformers: AA/AG/GG/GA = 28/35/28/9 was assumed in the final GED refinement. The more recent literature concerning the title molecule, as well as for several related molecules, has been examined and a survey has been attempted in the present article. The new experimental results for 3-chloropropanoyl chloride are discussed and compared with the previously published findings. 相似文献
197.
Bjoern Schnatwinkel Mikhail V. Rekharsky Victor V. Borovkov Jochen Mattay 《Tetrahedron》2009,65(13):2711-2715
The stability constants (K), standard free energy (ΔGo), enthalpy (ΔHo), and entropy changes (ΔSo) for the complexation of pyrogallol[4]arenes with ammonium cations of different size and shape have been determined in ethanol at 298 K by isothermal titration calorimetry. The trends observed in the thermodynamic parameters for 1:1 and/or 1:2 host-guest complexation correspond to the systematic structural changes of the guest molecules. On the basis of the results obtained we compare the complexation properties with two other resorcin[4]arenes and discuss the thermodynamic aspects of this supramolecular host-guest interactions. 相似文献
198.
199.
A.J. Qviller V.V. Yurchenko K. Eliassen J.I. Vestgården T.H. Johansen M.R. Nevala I.J. Maasilta K. Senapati R.C. Budhani 《Physica C: Superconductivity and its Applications》2010,470(19):897-900
Hysteretic effects are seen in the upper and lower threshold fields for the appearance of dendritic flux instabilities, first explained in Yurchenko et al. [Phys. Rev. B 76 (2007) 092504], in NbN-films. We have measured the threshold fields at increasing and decreasing applied fields at different temperatures and proposed a mechanism explaining how the hysteresis arises by analyzing the field profiles inside the sample. 相似文献
200.
We study the transversal motion of paramagnetic particles on a uniaxial garnet film, exhibiting a longitudinal ratchet effect in the presence of an oscillating magnetic field. Without the field, the thermal diffusion coefficient obtained by video microscopy is D(0) ≈ 3 × 10(-4) μm2/s. With the field, the transversal diffusion exhibits a giant enhancement by almost four decades and a pronounced maximum as a function of the driving frequency. We explain the experimental findings with a theoretical interpretation in terms of random disorder effects within the magnetic film. 相似文献