太阳风等离子体输出流量的全日面二维结构

本文根据1983年十个 Carrington 周(1733—1742)期间的 K-日冕亮度、行星际闪烁(IPS)观测和光球磁场观测,首次探讨了太阳风等离子体质量、动量和能量输出流量 F_M,F_P 和 F_E 的全日面二维平均结构及其与光球磁场结构的关系.     

Complex formation of isocytosine tautomers with PdII and PtII

Isocytosine (ICH) exists in solution as two major tautomers, the keto form with N1 carrying a proton (1a) and the keto form with N3 being protonated (1b). In water, 1a and 1b exist in equilibrium with almost equal amounts of both forms present. Reactions with a series of Pd(II) and Pt(II) am(m)ine species such as (dien)Pd(II), (dien)Pt(II), and trans-(NH(3))(2)Pt(II) reveal, however, a distinct preference of these metals for the N3 site, as determined by (1)H NMR spectroscopy. Individual species have been identified by the pD dependence of the ICH resonances. pK(a) values (calculated for H(2)O) for deprotonation of the individual tautomers complexes are 6.5 and 6.4 for the N3 linkage isomers of dienPd(II) and dienPt(II), respectively, as well as 6.2 and 6.0 for the N1 linkage isomers. The dimetalated species [(dienM)(2)(IC-N1,N3)](3+) (M = Pd(II) or Pt(II)) are insensitive over a wide range of pD. The crystal structure analysis of [(dien)Pd(ICH-N3)](NO(3))(2) is reported. Ab initio calculations have been performed for tautomer compounds of composition [(NH(3))(3)Pt(ICH)](2+), cis- and trans-[(NH(3))(2)PtCl(ICH)](+), as well as trans-[(NH(3))(2)Pt(ICH)(2)](2+). Without exception, N3 linkage isomers are more stable, in agreement with experimental findings. As to the reasons for this binding preference, an NBO (natural bond orbital) analysis for [(NH(3))(3)Pt(ICH-N3)](2+)strongly suggests that intramolecular hydrogen bonding between trans-positioned NH(3) ligands and the two exocyclic groups of the ICH is of prime importance. The calculations furthermore show a marked pyramidalization of the NH(2) group of ICH in the complex once the heterocyclic ligand forms a dihedral angle <90 degrees with the Pt coordination plane.     

Isocytosine as a hydrogen-bonding partner and as a ligand in metal complexes

Isocytosine (ICH; 1) exists in solution in an equilibrium of tautomers 1a and 1b with the N1 and N3 positions carrying the acidic proton, respectively. In the solid state, both tautomers coexist in a 1:1 ratio. As we show, the N3H tautomer 1b can selectively be crystallized in the presence of the model nucleobase 1-methylcytosine (1-MeC). The complex 1b x (1-MeC)2 x H2O (2) forms pairs through three hydrogen bonds between the components; hydrogen bonds between identical molecules are also formed, leading to an infinite tape structure. On the other hand, the N1H tautomer 1a co-crystallizes with protonated ICH to give [1a x ICH2]NO3 (3), again with three hydrogen bonds between the partners, yet the acidic proton is disordered over the two entities. With M(II)(dien) (M=Pt, Pd; dien=diethylenetriamine) preferential coordination of tautomer 1a through the N3 position is observed. DFT calculations, which were also extended to Pt(II)(tmeda) linkage isomers (tmeda=N,N,N',N'-tetramethylethylenediamine), suggest that intramolecular hydrogen bonding between the ICH tautomers and the co-ligands at M, while adding to the preference for N3 coordination, is not the major determining factor. Rather it is the inherently stronger Pt-N3 bond which favors complexation of 1a. With an excess of M(II)(dien), dinuclear species [M2(dien)2(IC-N1,N3)]3+ (M=Pd(II), 4 and Pt(II), 5) also form and were isolated as their ClO4(-) salts and structurally characterized. In strongly acidic medium 5 is converted to [Pt(dien)(ICH-N1)]2+ (6), that is, to the Pt(II) complex of tautomer 1b.     

Detection and measurement of noncoincidence between the principal axes of the g-matrix and zero-field splitting tensor using multifrequency powder EPR spectroscopy: application to cis-[(NH(3))(2)Pt(1-MeU)(2)Cu(H(2)O)(2)](SO(4)) x 4.5H(2)O (1-MeU = monoanion of 1-methyluracil)

Multifrequency continuous wave EPR spectra (4-34 GHz) on a powder of the title compound are consistent with a spin-triplet state. This arises from interaction between centrosymmetrically related pairs of copper(II) ions in the solid. The spectra at all frequencies have been simulated with a single set of spin-Hamiltonian parameters. The results show that there is noncoincidence between the principal axes of the g-matrices on each copper center and those of the zero-field splitting (D) tensor. This noncoincidence is a single rotation of 33 degrees +/- 2 degrees. The parameters from the powder spectra have been verified by a subsequent single-crystal EPR study which yielded the spin-Hamiltonian parameters g(XX) = 2.074, g(YY) = 2.093, g(ZZ) = 2.385, D(XX) = +/-0.0228 cm(-1), D(YY) = +/-0.0211 cm(-1), D(ZZ) = -/+0.0439 cm(-1) with Euler angles of alpha = 179 degrees, chi = 33.4 degrees, and gamma = 328 degrees. Analysis of the zero-field splitting tensor in terms of exchange indicates that the interaction between the pairs of copper(II) ions is almost entirely dipolar in origin. This study shows that multifrequency EPR spectroscopy on powders, coupled with spectrum simulation, can detect and measure noncoincidence between the principal axes of the g-matrix and zero-field splitting tensor, and does not necessarily require the presence of metal hyperfine interactions.     

Observation of the early stages of growth and the formation of growth spirals in epitaxial YBa2Cu3O7-δ thin films by AFM

Ultrathin epitaxial films of YBa₂Cu₃O_7– on SrTiO₃ prepared by Direct Current (DC) sputtering and pulsed laser deposition were imaged by Atomic Force Microscopy (AFM) to follow the different stages of growth of the thin films. Series of films with thicknesses between 1.2 nm and 12 nm (1–10 monolayers of YBa₂Cu₃O_7–) were prepared under identical conditions, optimized with respect to electrical and structural properties, to obtain information on the mechanisms responsible for the formation of growth spirals which are commonly observed in films having a thickness of several 10 nm or more. It could be shown that few layers are formed by a layered growth mode where material is attached laterally to 2D islands which are only one c-axis unit cell in height. In a later stage of growth when about 8–10 layers have been formed, the growth process changes to a mode which is mediated by growth spirals. This could be directly monitored in the AFM images where different defect structures like vertically sheared growth fronts and dendrite-like terraces of stacked islands as well as the resulting growth spirals could be identified.     

The Uracil C(5) Position as a Metal Binding Site: Solution and X-ray Crystal Structure Studies of Pt(II) and Hg(II) Compounds

1,3-Dimethyluracil (1,3-DimeU) reacts with trans-[(CH(3)NH(2))(2)Pt(H(2)O)(2)](+) to give trans-[(CH(3)NH(2))(2)Pt(1,3-DimeU-C5)(H(2)O)]X (X = NO(3)(-), 1a, ClO(4)(-), 1b) and subsequently with NaCl to give trans-(CH(3)NH(2))(2)Pt(1,3-DimeU-C5)Cl (2) or with NH(3) to yield trans-[(CH(3)NH(2))(2)Pt(1,3-DimeU-C5)(NH(3))]ClO(4) (3). In a similar way, (dien)Pt(II) forms [dienPt(1,3-DimeU-C5)](+) (4). Reactions leading to formation of 1 and 4 are slow, taking days. In contrast, Hg(CH(3)COO)(2) reacts fast with 1,3-DimeU to give (1,3-DimeU-C5)Hg(CH(3)COO) (5). Both 1-methyluracil (1-MeUH) and uridine (urdH) react with (dien)Pt(II) initially at N(3) and subsequently with either (dien)Pt(II) or Hg(CH(3)COO)(2) also at C(5) to give the diplatinated species 7 and 9 or the mixed PtHg complex 8. C(5) binding of either Pt(II) or Hg(II) is evident from coupling of uracil-H(6) with either (195)Pt or (199)Hg nuclei and (3)J values of 47-74 Hz (for Pt compounds) and 185-197 Hz (for Hg compounds). J values of Pt compounds are influenced both by the ligands trans to the uracil C(5) position and by the number of metal entities bound to a uracil ring. Both 2 and 5 were X-ray structurally characterized. 2: monoclinic system, space group P2(1)/c, a = 15.736(6) ?, b = 11.481(6) ?, c = 25.655 (10) ?, beta = 145.55(3) degrees, V = 2621.9(28) ?(3), Z = 4. 5: monoclinic system, space group P2(1)/c, a = 4.905(2) ?, b = 18.451(6) ?, c = 11.801(5) ?, beta = 94.47(3) degrees, V = 1064.77(72) ?(3), Z = 4.     

Preparation of epitaxial La0.6Ca0.4Mn1−xFexO3 (x = 0, 0.2) thin films: Variation of the oxygen content

Perovskite thin films with a nominal composition of La_0.6Ca_0.4Mn_1−xFe_xO₃ (x = 0, 0.2) were deposited by pulsed reactive crossed beam laser ablation. The film properties, such as electrical conductivity and magnetoresistance are studied as a function of the oxygen content and substrate type. The oxygen content of the thin films was determined by Rutherford Backscattering and controlled by varying the background gas pressure, pressure of the gas pulse and by using alternatively O₂ and N₂O as the gas pulse.

LaAlO₃ and SrTiO₃ were used as substrates at deposition temperature of 650 °C. The grown films were analyzed by X-ray diffraction in order to optimize the growth conditions, i.e. to obtain epitaxial thin films. Thin films doped with 20% Fe were grown under the same experimental conditions as the undoped LCMO films and the effect of the doping on the structural and transport properties of the thin films has been investigated.

The temperature of the metal–insulator transition was measured as a function of the oxygen content and substrate type.     

Dynamics of photoinduced processes in adenine and thymine base pairs

The excited-state dynamics of adenine and thymine dimers and the adenine-thymine base pair were investigated by femtosecond pump-probe ionization spectroscopy with excitation wavelengths of 250-272 nm. The base pairs showed a characteristic ultrafast decay of the initially excited pi pi* state to an n pi* state (lifetime tau(pi pi*) approximately 100 fs) followed by a slower decay of the latter with tau(n pi*) approximately 0.9 ps for (adenine)2, tau(n pi*) = 6-9 ps for (thymine)2, and tau(n pi*) approximately 2.4 ps for the adenine-thymine base pair. In the adenine dimer, a competing decay of the pi pi* state via the pi sigma* state greatly suppressed the n pi* state signals. Similarities of the excited-state decay parameters in the isolated bases and the base pairs suggest an intramonomer relaxation mechanism in the base pairs.