Hydrogen molecule in the small dodecahedral cage of a clathrate hydrate: quantum translation-rotation dynamics at higher excitation energies

Higher-lying five-dimensional translation-rotation (T-R) eigenstates of a single p-H2 and o-D2 molecule confined inside the small dodecahedral (512) cage of the structure II clathrate hydrate are calculated rigorously, as fully coupled, with the cage assumed to be rigid. The calculations cover the excitation energies up to and beyond the j=2 rotational level of the free molecule, 356 cm(-1) for H2 and 179 cm(-1) for D2. It is found that j is a good quantum number for all the T-R states of p-H2, j=0 and j=2, considered. The same is not true for o-D2, where a number of T-R states in the neighborhood of the j=2 level show significant mixing of j=0 and j=2 rotational basis functions. The 5-fold degeneracy of the j=2 level of p-H2 is lifted completely due to the anisotropy of the cage environment, as is the 3-fold degeneracy of the j=1 level of o-H2 studied by us previously. Pure translational mode excitations with up to four quanta display negative anharmonicity, which was observed earlier for the translational fundamentals and their first overtones. The issues of assigning the combination states of p-H2 with excitations of two or all three translational modes, and of the strength of the mode coupling as a function of the excitation energy, are studied carefully for a range of quantum numbers. The average T-R energy of the encapsulated p-H2 is calculated as a function of temperature from 0 to 150 K.     

Polysubstituted 5-Phenylazopyrimidines: Extremely Fast Non-ionic Photochromic Oscillators

Photochromic systems with an ultrahigh rate of thermal relaxation are highly desirable for the development of new efficient photochromic oscillators. Based on DFT calculations, we designed a series of 5-phenylazopyrimidines with strong push–pull character in silico and observed very low energy barriers for the thermal (Z)-to-(E) isomerization. The structure of the (Z)-isomer of the slowest isomerizing derivative in the series was confirmed by NMR analysis with in situ irradiation at low temperature. The substituents can tune the lifetime of thermal back isomerization from hundreds of microseconds to several nanoseconds (8 orders of magnitude). The photoswitching parameters were extracted from transient absorption techniques and a dominant rotation mechanism of the (Z)-to-(E) thermal fading was proposed based on DFT calculations.     

Assembly of the first fullerene-type metal-organic frameworks using a planar five-fold coordination node

Pump up the volume: Slow crystallization of Na[C(5) (CN)(5) ], the unsolvated sodium salt of pentacyanocyclopentadienide, gives the first example of an anionic coordination network based on metal-fullerene units. The structure of this network is closely related to a type?I gas clathrate in which around 66?% of the unit cell volume is occupied by solvent molecules.     

Surface‐enhanced Raman scattering on colloid gels originated from low molecular weight gelator

Surface‐enhanced Raman scattering (SERS) on silver and gold colloid gels formed by a low molecular weight organic gelator, bis‐(S‐phenylalanine) oxalyl amide, was obtained. Strong Raman signals dominate in the SERS spectra of hydrogels containing silver nanoparticles prepared by citrate and borohydride reduction methods, whereas broad bands of low intensity are detected in the spectra of gold colloid gels. Resemblance between Raman spectrum of the crystalline substance and the SERS spectra of the silver nanoparticle–hydrogel composites implies the electromagnetic nature of the signal enhancement. A change in Raman intensity of the benzene and amide II bands caused by an increase in temperature and concentration indicates that the gelling molecules are strongly attached through the benzene moieties to the metal nanoparticles while participating in gel formation by intermolecular hydrogen bonding between the adjacent oxalyl amide groups. Transmission electron microscopy reveals a dense gel structure in the close vicinity of the enhancing metal particles for both silver colloid gels. Copyright © 2008 John Wiley & Sons, Ltd.     

Epitaxial growth of the metastable phase ytterbium monoxide on gallium nitride surfaces

Molecular beam deposition systems allow for unparalleled control of film composition and structure. This article addresses the capacity for controlling metal and oxidant fluxes in the Yb/O₂ system to access the metastable phase ytterbium monoxide (YbO). Experiments exploring the growth of polycrystalline YbO_x films by molecular beam deposition demonstrate that a 2:1 molar ratio of Yb:O₂ fluxes is necessary to achieve preferential growth of the divalent oxide. Applying similar deposition conditions to a (0 0 1) GaN surface leads to the growth of epitaxial (1 1 1) YbO films. Similar to other rocksalt oxides grown on GaN surfaces, YbO films display a 3D growth mechanism that leads to a grainy morphology with crystallites of 50 nm lateral dimensions. Rocking curves in ω and φ have full-width half-maximum values of 1.77° and 4.1°, respectively; further improvements in crystal quality appear to be limited by the thermal stability of the YbO phase.     

Calculation of coefficients of a cardinal B-spline

It is well known that a cardinal B-spline of order $m,m\in \mathbb{N}$, is a piecewise polynomial function. In this note we propose an effective method for calculating the coefficients of polynomials which constitute a cardinal B-spline.     

Magnetic curves in Sol3

Magnetic curves with respect to the canonical contact structure of the space Sol₃ are investigated.     

Quantum criticality of D-wave quasiparticles and superconducting phase fluctuations

We present finite temperature (T) extension of the (2+1)-dimensional QED (QED3) theory of under-doped cuprates. The theory describes nodal quasiparticles whose interactions with quantum proliferated hc/2e vortex-antivortex pairs are represented by an emergent U(1) gauge field. Finite T introduces a scale beyond which the spatial fluctuations of vorticity are suppressed. As a result, the spin susceptibility of the pseudogap state is bounded by T2 at low T and crosses over to approximately T at higher T, while the low-T specific heat scales as T2, reflecting the thermodynamics of QED3. The Wilson ratio vanishes as T-->0; the pseudogap state is a "thermal (semi)metal" but a "spin-charge dielectric." This non-Fermi liquid behavior originates from two general principles: spin correlations induced by "gauge" interactions of quasiparticles and fluctuating vortices and the "relativistic" scaling of the T=0 fixed point.     

Instability of the spiral state of the doped Hubbard model

It is shown that the homogeneous spiral state of the doped Hubbard model is unstable for infinitesimal doping concentration. The spin response about the Hartree-Fock spiral state is evaluated, considering both the interband and intraband processes. Driven by long-wavelength, intraband spin fluctuations, the instability towards infinitesimal fluctuations about the mean-field state is inferred from the nature of the static spin response.