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Poulsen MD Peronne E Stapelfeldt H Bisgaard CZ Viftrup SS Hamilton E Seideman T 《The Journal of chemical physics》2004,121(2):783-791
The rotational revival structure of asymmetric top molecules, following irradiation by an intense picosecond laser pulse, is explored theoretically and experimentally. Numerically we solve nonperturbatively for the rotational dynamics of a general asymmetric top subject to a linearly polarized intense pulse, and analyze the dependence of the dynamical alignment on the field and system parameters. Experimentally we use time-resolved photofragment imaging to measure the alignment of two molecules with different asymmetry, iodobenzene, and iodopentafluorobenzene. Our numerical results explain the experimental observations and generalize them to other molecules. The rotational revival structure of asymmetric tops differs qualitatively from the intensively studied linear top case. Potentially it provides valuable structural information about molecules. 相似文献
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Hella Folkerts Kurt Dehnicke Jrg Magull Helmut Goesmann Dieter Fenske 《无机化学与普通化学杂志》1994,620(7):1301-1306
Phosphorane Iminato-Trichloroselenates(II): Syntheses and Crystal Structures of [SeCl(NPPh3)2]+SeCl3? and [Me3SiN(H)PMe3]2+[Se2Cl6]2? [SeCl(NPPh3)2]+SeCl3? has been synthesized by the reaction of Se2Cl2 with Me3SiNPPh3 in acetonitrile solution, forming orangered crystals, whereas red crystals of [Me3SiN(H)PMe3]2+[Se2Cl6]2? were obtained by the reaction of Me3SiNPMe3 with SeOCl2 in acetonitrile solution. Both complexes were characterized by X-ray structure determinations. [SeCl(NPPh3)2]+SeCl3?: Space group P21/n, Z = 4, structure solution with 7 489 observed unique reflections, R = 0.057. Lattice dimensions at ?60°C: a = 1 117.0; b = 2 241, c = 1 407.5 pm, β = 95.61°. In the cation [SeCl(NPPh3)2]+ the selenium atom is φ-tetrahedrally coordinated by the chlorine atom and by the nitrogen atoms of the phosphorane iminato ligands, whereas the anion SeCl3? has a T-shaped structure with φ-trigonal-bipyramidale surrounding of the selenium atom. [Me3SiN(H)PMe3]2+[Se2Cl6]2?: Space group P21/c, Z = 4, structure solution with 2 093 observed unique reflections, R = 0.080. Lattice dimensions at ?70°C: a = 956, b = 828, c = 1 973 pm, β = 93.80°. The structure consists of [Me3SiN(H)PMe3]+ ions and planar [Se2Cl6]2? anions, in which the selenium atoms are bridged nearly symmetrically by two chlorine atoms. 相似文献
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E. Y. Vedmedenko N. Mikuszeit T. Stapelfeldt R. Wieser M. Potthoff A. I. Lichtenstein R. Wiesendanger 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,80(3):331-336
Using exact diagonalization, Monte-Carlo, and mean-field techniques, characteristic temperature scales for ferromagnetic order
are discussed for the Ising and the classical anisotropic Heisenberg model on finite lattices in one and two dimensions.
The interplay between nearest-neighbor exchange, anisotropy and the presence of surfaces leads, as a function of temperature,
to a complex behavior of the distance-dependent spin-spin correlation function, which is very different from what is commonly
expected.
A finite experimental observation time is considered in addition, which is simulated within the Monte-Carlo approach by an
incomplete statistical average.
We find strong surface effects for small nanoparticles, which cannot be explained within a simple Landau or mean-field concept
and which give rise to characteristic trends of the spin-correlation function in different temperature regimes.
Unambiguous definitions of crossover temperatures for finite systems and an effective method to estimate the critical temperature
of corresponding infinite systems are given. 相似文献
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In this paper we prove that thek-ary fragment of transitive closure logic is not contained in the extension of the (k–1)-ary fragment of partial fixed point logic by all (2k–1)-ary generalized quantifiers. As a consequence, the arity hierarchies of all the familiar forms of fixed point logic are strict simultaneously with respect to the arity of the induction predicates and the arity of generalized quantifiers.Although it is known that our theorem cannot be extended to the sublogic deterministic transitive closure logic, we show that an extension is possible when we close this logic under congruence.Supported by a grant from the University of Helsinki. This research was initiated while he was a Junior Researcher at the Academy of FinlandThis article was processed by the author using the LATEX style filepljourlm from Springer-Verlag. 相似文献
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We demonstrate, theoretically and experimentally, that an intense, elliptically polarized, nonresonant laser field can simultaneously force all three axes of a molecule to align along given axes fixed in space, thus inhibiting the free rotation in all three Euler angles. Theoretically, the effect is illustrated through time dependent quantum mechanical calculations. Experimentally, 3, 4-dibromothiophene molecules are aligned with a nanosecond laser pulse. The alignment is probed by 2D ion imaging of the fragments from a 20 fs laser pulse induced Coulomb explosion. 相似文献
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The need to develop reliable and efficient adaptive algorithms using mixed finite element methods arises from various applications in fluid dynamics and computational continuum mechanics. In order to save degrees of freedom, not all but just some selected set of finite element domains are refined and hence the fundamental question of convergence requires a new mathematical argument as well as the question of optimality. We will present a new adaptive algorithm for mixed finite element methods to solve the model Poisson problem, for which optimal convergence can be proved. The a posteriori error control of mixed finite element methods dates back to Alonso (1996) Error estimators for a mixed method. and Carstensen (1997) A posteriori error estimate for the mixed finite element method. The error reduction and convergence for adaptive mixed finite element methods has already been proven by Carstensen and Hoppe (2006) Error Reduction and Convergence for an Adaptive Mixed Finite Element Method, Convergence analysis of an adaptive nonconforming finite element methods. Recently, Chen, Holst and Xu (2008) Convergence and Optimality of Adaptive Mixed Finite Element Methods. presented convergence and optimality for adaptive mixed finite element methods following arguments of Rob Stevenson for the conforming finite element method. Their algorithm reduces oscillations, before applying and a standard adaptive algorithm based on usual error estimation. The proposed algorithm does this in a natural way, by switching between the reduction of either the estimated error or oscillations. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Journal of Statistical Physics - The study and analysis of real-world social, communication, information and citation networks for understanding their structure and identifying interesting patterns... 相似文献
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