The photodetachment spectrum of OHF−: the influence of vibration at a transition state

New ab initio potential energy functions for collinear OHF^? and OHF have been used with time-dependent wavepacket studies in a simulation of the photodetachment spectrum of the OHF^? anion. Franck—Condon excitation of OHF^? lies within the transition state region for the bimolecular reaction F + OH ? O + HF on the lowest triplet surface. The branching ratios for fragmentation of the excited OHF are such that the peaks in this spectrum may each be correlated with dissociation to a single vibrational state of the O + HF(v) or OH(v) + F products. The possible influence of vibrational excitation of the anion has been explored also. This is predicted to lead to marked changes in the spectra. Experimental observations of such spectra could be used in refinement of the potential as could an experiment in which the electron kinetic energy is detected in coincidence with the vibrational states of the molecular products or with the kinetic energy of the atomic products. The calculations revealed a number of metastable resonances on the OHF surface, although these are all at higher energies than are relevant to the photodetachment spectrum from the ground state anion.     

Molecular dynamic studies of the interaction of a/6⟨112⟩ Shockley dislocations with stacking fault tetrahedra in copper. Part II: Intersection of stacking fault tetrahedra by moving twin boundaries

The interactions of moving twin boundaries with stacking fault tetrahedra (SFTs) have been studied by molecular dynamics. The results reveal a spectrum of processes occurring during these interactions. In general, they lead to damage of the parent SFT and formation of new defects in the twin lattice. The character of these defects depends on the nature of the twinning front, the size of the SFT and its orientation with respect to incoming dislocations. Typical structures that may be produced in the twin include product-SFTs, free vacancies, planar stacking faults bounded by partial dislocations, mutually linked stacking faults on non-coplanar {111} _T planes, small {111} _T tetrahedra and their partial forms. Dislocation mechanisms involved in the formation of these defects are being analyzed.     

Enhanced red fluorescence in Sr2Si1−xGexO4:Eu3+ phosphors by the substitution of Si by Ge for white light emitting diodes

Eu³⁺-doped Sr₂Si_1?xGe_xO₄ (x=0–1) phosphors have been prepared by the high temperature solid-state reaction method. The luminescent properties of these phosphors were investigated. Red fluorescence of Eu³⁺ is enhanced gradually in the samples with increasing substitution of Si by Ge upon the excitation of 393 nm light. The intensity is increased by 50% with full substitution of Si by Ge. These results are originated from the structural changes and the phonon energy reduction in the samples due to the substitution of Si by Ge. The CIE chromaticity coordinates of the phosphors vary slightly around (0.62, 0.37) and all are in the red color region. The results indicate that these phosphors could be promising red phosphors for white light emitting diodes.     

Influence of charge carriers on magnetic order in lightly doped manganites, detected by μSR: Evidence for a superparamagnetic transition to the antiferromagnetic state

We detected two spontaneous precession frequencies in antiferromagnetic pure LaMnO₃, the end member of different families of charge-doped manganites. The muon site and local field orientation are identified for one frequency, which provides a measure of the staggered magnetization. We present additional zero and longitudinal field muon relaxation data on an LaMnO_3.045 sample in which a new regime appears above an intermediate temperatureT*, where regions of magnetic order coexist with domains of fluctuating moments. These results are discussed in terms of nucleation of the ordered phase in a superparamagnetic matrix.     

Torsional tunneling splittings in the v4 = 1 excited torsional state of Si2H6: analysis of hot bands accompanying fundamental transitions in the high resolution infrared spectrum

The (ν₄?+?ν₆)???ν₄, (ν₄?+?ν₈)???ν₄ and (ν₄?+?ν₉)???ν₄ hot infrared systems of disilane (Si₂H₆) have been analysed at high resolution, and the values of the relative vibration–rotation–torsion parameters have been determined. The torsional splitting is about 0.500?cm^?1 in the ν₄ and ν₄?+?ν₆ states, and decreases strongly in the vibrationally degenerate upper states ν₄?+?ν₈ (about 0.0272?cm^?1 on average) and ν₄?+?ν₉ (about 0.3019?cm^?1), consistent with theoretical predictions. Comparison between the vibrational wavenumbers of cold transitions and hot transitions originating in the excited torsional state v₄?=?1 allows one to determine the change of the fundamental torsional frequency ν₄ caused by the excitation of small amplitude vibrations. A remarkable increase in ν₄ of about 8.599?cm^?1 is found in the v₉?=?1 state (E_1d SiH₃-rocking mode, asymmetric to inversion in the staggered geometry), and this corresponds to an increase in the torsional barrier height in this excited fundamental vibrational state by about 48.77?cm^?1. The mechanism responsible for the decrease of the torsional splittings in the degenerate vibrational states is briefly outlined by means of second-order perturbation theory, using torsion-hindered vibrational basis functions of E_1d and E_2d symmetries for the degenerate modes.     

Anomalous charge transfer in La<Subscript>2</Subscript>CuO<Subscript>4</Subscript> near the Néel temperature: Evidence of the transition from spin liquid to two-sublattice antiferromagnetic state

The temperature dependence of the electrical resistance and thermopower of La_{2? x}Sr_xCuO_4+δ single crystals with x ? 0.003 and δ<0.05 has been studied in the temperature range from 100 to 400 K. All crystals exhibiting two-dimensional hopping conductivity via neighboring acceptor sites in the CuO₂ plane show a significant difference in the charge transfer below and above the Néel temperature T_N. This difference indicates that the loss of a two-sublattice antiferromagnetic order strongly affects the charge transport in the CuO₂ plane. The obtained data lead to a conclusion that the crystal above T_N occurs in a resonance valence bond state of the Bose type.     

Heteroepitaxy of GexSi1 ? x (x ～ 0.4–0.5) films on Si(001) substrates misoriented to (111): Formation of short edge misfit dislocations alone in the misorientation direction

Relaxation of mechanical misfit stresses in Ge _x Si_{1 − x} (x ∼ 0.4–0.5) epitaxial films grown by molecular epitaxy on Si substrates misoriented from the exact orientation (001) by an angle of 6° has been studied. Possible cases of induced nucleation and interaction of 60° misfit dislocations (MDs) propagating in the misorientation direction with the formation of short edge MD segments are considered. Such configurations are classified and their various forms experimentally detected by TEM are presented. It is shown that short edge MDs are formed by two different mechanisms: (A) correlated or induced nucleation of a complementary 60° dislocation half-loop followed by the formation of an edge dislocation segment; and (B) the formation of a 90° MD segment upon intersection of the already existing complementary 60° MDs gliding in oppositely inclined {111} planes. The nonequivalency of the interaction of 60° MDs propagating in opposite directions along the substrate misorientation is shown.