Photopolymerization in the Fullerene Layers of the Molecular Donor–Acceptor Complex {Pt(nPr2dtc)2} · (C60)2

We measured Raman spectra in crystals of molecular donor–acceptor fullerene complexes {Me(nPr₂dtc)₂} · (C₆₀)₂ (Me = Ni, Cu, Pt). In the spectra of the {Pt(nPr₂dtc)₂} · (C₆₀)₂ complex under prolonged irradiation with a laser with λ = 532 nm, characteristic changes in the photopolymerization of fullerene are observed, associated with the splitting of degenerate phonon Hg modes and softening of Ag modes of the C₆₀ molecule. The kinetics of photopolymerization under conditions of weak irradiation at room temperature is studied. It was found that thermal destruction of the photopolymer with increasing temperature leads to a decrease in its concentration in the final photopolymerization product. The kinetics of thermal destruction is described by the Arrhenius equation, with the activation energy E_A of (0.68 ± 0.03) eV; the dimers are destructed to a concentration of 1% within 15 min at ~114°C.

     

Phase transitions in the ferroelectrics (Sn1−x In(2/3)x )2P2S6 at high pressures

New ferroelectric solid solutions (Sn_1−x In_(2/3)x )₂P₂S₆ were investigated at high hydrostatic pressures. The range in which the incommensurate structure exists was determined. A dynamic shift of the incommensurate-ferroelectric phase transition temperature with increasing rate of change of temperature and the appearance of “reverse hysteresis” were observed. The characteristic features in the appearance of the latter effect in these crystals are investigated. Fiz. Tverd. Telsa (St. Petersburg) 41, 1276–1278 (July 1999)     

Magnetic properties of crystals of the molecular complex between fullerene C60 and an organic donor 9,9′-trans-bis(telluraxanthenyl)

The EPR and static magnetic susceptibility of the crystalline molecular complex between fullerene C60 and an organic donor 9,9′-trans-bis(telluraxanthenyl) (BTX) have been measured as functions of temperature. At temperatures T above 130 K, the samples exhibit anomalously high magnetic susceptibility exceeding the values calculated under the assumption that each molecule bears one paramagnetic spin 1/2. A very intense magnetic resonance signal is also observed in the samples in the region of high g factors (g>4.5). This allows the suggestion that the samples under study possess ferromagnetism (or superparamagnetism). The EPR signal and magnetic susceptibility sharply decay almost to zero as the temperature decreases below 100–120 K. It is supposed that electron transfer from donor molecules BTX to C60 molecules takes place at temperatures above 110 K. This electron transfer generates electron spins in the system, whereas the anomalously high magnetism is due to ferromagnetic correlations in the system of these spins.     

A 480 ms isomeric 29/2−-state of the(p_{1/2}^{ - 2} )_{0^ + } f_{5/2}^{ - 1} (i_{13/2}^{ - 2} )_{12^ + } configuration in203Pb

A new, 480 ms, 29/2^? isomeric level has been found in²⁰³Pb at an excitation energy of 2950.1 keV by bombarding²⁰⁴Hg with α-particles in the energy range 45–55 MeV using the Stockholm 225-cm cyclotron. This 29/2^? state is suggested to be mainly due to the configuration (p ₁ ^2/?2 f ₅ ^2/?1 i ₁₃ ^2/?2 )₁₂. The 29/2^? state decays predominantly by a 153.4 keV M2 transition to a 23/2^? level and by a 1027.5 keV M4 transition to a 21/2⁺ level, followed by two E2 transitions of energies 258.6 keV and 838.7 keV, respectively, to the previously known 13/2⁺, 6.4 s isomeric level. The decay scheme of the 29/2^? isomeric state is based on experimental information obtained from total and delayedγ-ray intensities,γγ-coincidences, excitation functions, lifetime and delayed conversion electron measurements. The presence of the 29/2^? level confirms an essential and expected feature of the shell model for five neutron holes added to the²⁰⁸Pb-core.     

Phase transitions in the (Cs1−x Rbx)2ZnI4 system

(Cs_1−x Rb_x)₂ZnI₄ crystals were grown by two different methods with Rb concentrations varying from x=0 to 2.5%. ¹²⁷I NQR and calorimetric measurements showed that crystals grown by the Bridgman technique contain residual impurities (∼0.5%) for all x. While x=0 crystals grown from solution do not contain detectable impurities, they allow incorporation only of a low Rb concentration, not above 0.5%. A transition-temperature-concentration (x) phase diagram has been constructed for Bridgman-grown crystals from NQR data. Rb doping shifts the normal-incommensurate and incommensurate-ferroelastic phase-transition points toward higher temperatures with different rates. The P2₁/m↔P1 first-order transition shifts toward lower temperatures. The region of low Rb concentrations lies closest to the critical point. Fiz. Tverd. Tela (St. Petersburg) 41, 143–147 (January 1999)     

Phase transformations in the TiO2–SiO2 system at high pressures and temperatures

In situ X-ray diffraction study of a sol–gel-produced SiO₂–TiO₂ glass and intimately mixed ultrafine powders of SiO₂ and TiO₂ was used to investigate the effect of TiO₂ on the high-pressure phase transformations of SiO₂ and specifically on the change in the p,T-conditions of the formation of coesite and stishovite. Our findings have shown that at pressures to 7.5?GPa and temperatures up to 1300?K the presence of TiO₂ does not favor the formation of stishovite.     

Nonequilibrium crystal-to-amorphcs phase transitions in “high pressure” phases SiOz and Ge(A1)

Abstract

The pressure dependences of the temperatures of the crystal-to-amorphous transformations for SiO₂ and Geo.7Alo.9 are presented. The field of the existence of amorphous phases of both substances vanishes at high pressure.

Les variations avec P de la temperature de transformations cristal-to-amorphous de SiO₂ et Ga. 7 Ala. 9 sont presentes. Le champ d'existence de phase amorphe de ces substances desparait a haute pression.     

Role of the Λ(1600) in the ${K}^{-}p \rightarrow {\rm{\Lambda }}{\pi }^{0}{\pi }^{0}$ reaction

Role of the Λ(1600) is studied in the ${K}^{-}p\to {\rm{\Lambda }}{\pi }^{0}{\pi }^{0}$ reaction by using the effective Lagrangian approach near the threshold. We perform a calculation for the total and differential cross sections by considering the contributions from the Λ(1600) and Λ(1670) intermediate resonances decaying into ${\pi }^{0}{{\rm{\Sigma }}}^{* 0}(1385)$ with ${{\rm{\Sigma }}}^{* 0}(1385)$ decaying into ${\pi }^{0}{\rm{\Lambda }}$. Additionally, the non-resonance process from u-channel nucleon pole is also taken into account. With our model parameters, the current experimental data on the total cross sections of the ${K}^{-}p\to {\rm{\Lambda }}{\pi }^{0}{\pi }^{0}$ reaction can be well reproduced. It is shown that we really need the contribution from the Λ(1600) with spin-parity ${J}^{P}=1/{2}^{+}$, and that these measurements can be used to determine some of the properties of the Λ(1600) resonance. Furthermore, we also plot the π⁰Λ invariant mass distributions which could be tested by the future experimental measurements.     

Phase transitions of YbX (X = P,As and Sb) with a NaCl-type structure at high pressures

The powder X-ray diffraction of YbX (X?=?P, As and Sb) with a NaCl-type structure has been studied with synchrotron radiation up to 63?GPa at room temperature. YbSb undergoes the first-order structural phase transition from the NaCl-type (B1) to the CsCl-type (B2) structure at around 13?GPa. The structural change to the B2 structure occurs with the volume collapse of about 1% at 13?GPa. The transition pressure of YbSb is surprisingly lower than that of any other heavier LnSb (Ln?=?Dy, Ho, Er, Tm and Lu). The pressure-induced phase transitions in YbP and YbAs are observed at around 51?GPa and 52?GPa respectively. The transition pressure of both compounds is much higher than that of YbSb. The high-pressure structural behaviour of YbX (X?=?P, As and Sb) is discussed. The volume versus pressure curve for YbX with the NaCl-type structure is fitted by a Birch equation of state. The bulk moduli of these compounds with the NaCl-type structure are 104?GPa for YbP, 85?GPa for YbAs and 52?GPa for YbSb.     

Phases and phase transitions in the mixed molecular system (NaCN)1−x(KCN)x

The phase diagram of (NaCN)_1–x(KCN)_x was examined by neutron powder diffraction in the temperature range 5K T300 K. Several non-cubic low-temperature phases were identified for concentrationsx<x _c1=0.15 andxx _c2=0.89. Lattice parameters and ferroelastic deformations were determined from the observed powder patterns. The phase transformations were characterized following the temperature dependence of the appropriate order parameters.     

A fresh look at η 2(1645), η 2(1870), η 2(2030) and f 2(1910) in \bar{p}p \to \eta \pi ^{0}\pi ^{0}\pi ^{0}

There is a large discrepancy between results of Crystal Barrel and WA102 for the branching ratio R=BR[η ₂(1870)→a ₂(1320)π]/BR[η ₂(1870)→f ₂(1270)η]. An extensive re-analysis of the Crystal Barrel data redetermines branching ratios for decays of η ₂(1870), η ₂(1645), η ₂(2030) and f ₂(1910). This re-analysis confirms a small value for R of 1.60±0.39, inconsistent with the value 20.4±6.6 of WA102. The likely origin of the discrepancy is that the WA102 data contain a strong f ₂(1910)→a ₂ π signal as well as η ₂(1870). There is strong evidence that the η ₂(1870) has resonant phase variation. A peak in f ₂(1270)a ₀(980) confirms closely the parameters of the a ₂(2255) resonance observed previously. A peak in η ₂(2030)π is interpreted naturally in terms of π ₂(2245) with reduced errors for mass and width M=2285±20(stat)±25(syst) MeV, Γ=250±20(stat)±25(syst) MeV.     

Fundamental Role of the H-Bond Interaction in the Dissociation of NH_{3} on Si(001)-(2×1)

Further insight into the dissociative adsorption of NH_{3} on Si(001) has been obtained using a combined computational and experimental approach. A novel route leading to the dissociation of the chemisorbed NH_{3} is proposed, based on H-bonding interactions between the gas phase and the chemisorbed NH_{3} molecules. Our model, complemented by synchrotron radiation photoelectron spectroscopy measurements, demonstrates that the low temperature dissociation of molecular chemisorbed NH_{3} is driven by the continuous flux of ammonia molecules from the gas phase.     

Phase transitions in a metal–organic coordination polymer: [Zn2(C8H4O4)2(C6H12N2)] with guest molecules. Thermal effects and molecular mobility

Thermal effects of a series of [Zn₂(C₈H₄O₄)₂(C₆H₁₂N₂)] porous compound with the guest molecules located in the pores were studied using differential scanning calorimetry combined with solid-state ¹H nuclear magnetic resonance spectroscopy. The intercalation of the molecules was shown to produce various thermal anomalies and phase transitions, which were characterized and analyzed.     

$\mathcal {}$-Matrix-valued Wave Packet Frames in L2(ℝd,ℂs×r)$L^{2}(\mathbb {R}^{d}, \mathbb {C}^{s\times r})$

We study frame properties of a matrix-valued wave packet system in the matrix-valued function space \(L^{2}(\mathbb {R}^{d}, \mathbb {C}^{s\times r})\), where the lower frame condition is controlled by a bounded linear operator \(\mathcal {K}\) on \(L^{2}(\mathbb {R}^{d}, \mathbb {C}^{s\times r})\) (lower \(\mathcal {K}\)-frame condition, in short). There are many differences between ordinary frames and \(\mathcal {K}\)-frames. The lower \(\mathcal {K}\)-frame condition for matrix-valued wave packet Bessel sequences in \(L^{2}(\mathbb {R}^{d},\mathbb {C}^{s\times r})\) in terms of operators; a trace functional associated with a bounded linear operator on \(L^{2}(\mathbb {R}^{d}, \mathbb {C}^{s\times r})\); and a series associated with a matrix-valued Bessel sequence is presented. It is shown that matrix-valued wave packet frames are stable under small perturbation with respect to wave packet window functions.     

The S-wave resonance contributions in the $$B^{0}_{s}$$ decays into $$\psi (2S,3S)$$ψ(2S,3S) plus pion pair

The three-body decays \(B^0_s \rightarrow \psi (2S,3S) \pi ^+ \pi ^-\) are studied based on the perturbative QCD approach. With the help of the nonperturbative two-pion distribution amplitudes, the analysis is simplified into the quasi-two-body processes. Besides the traditional factorizable and nonfactorizable diagrams at the leading order, the next-to-leading order vertex corrections are also included to cancel the scale dependence. The \(f_0(980)\), \(f_0(1500)\) resonance contributions as well as the nonresonant contributions are taken into account using the presently known \(\pi \pi \) time-like scalar form factor for the \(s\bar{s}\) component. It is found that the predicted \(B^0_s \rightarrow \psi (2S) \pi ^+ \pi ^-\) decay spectra in the pion pair invariant mass shows a similar behavior as the experiment. The calculated S-wave contributions to the branching ratio of \(B^0_s \rightarrow \psi (2S) \pi ^+ \pi ^-\) is \(6.0\times 10^{-5}\), which is in agreement with the LHCb data \(\mathcal {B}(B^0_s \rightarrow \psi (2S) \pi ^+ \pi ^-)=(7.2\pm 1.2)\times 10^{-5} \) within errors. The estimate of \(\mathcal {B}(B^0_s \rightarrow \psi (3S) \pi ^+ \pi ^-)\) can reach the order of \(10^{-5}\), pending the corresponding measurements.     

Data on Neutron–Neutron Scattering Length from the Reaction $$\boldsymbol{n+^{2}\textrm{H}\to n+n+p}$$ at $$\boldsymbol{E_{n}=60}$$ MeV

Physics of Atomic Nuclei - The $${}^{1}S_{0}$$ neutron–neutron ( $$nn$$ ) scattering length was measured in the neutron–deuteron ( $$nd$$ ) breakup reaction at an energy of 60 MeV. The...