Nonclassical rotations of single molecules in small helium and hydrogen clusters: Manifestation of “microscopic superfluidity”

The studies of small helium clusters (up to 100 atoms) and molecular-hydrogen clusters (up to 20 molecules) that are formed in a supersonic gas jet and are coupled by the weak van der Waals interaction with a linear chromophore molecule are reviewed The shift of the frequency of the fundamental vibration of the chromophore, as well as a change in the moment of inertia of a cluster with its growth, has been detected by their rotational and vibrational-rotational spectra. A nonclassical behavior of the moment of inertia manifested in its decrease beginning with a certain number of attached He atoms (H₂ molecules) has been revealed. This behavior indicates that a part of a cluster is decoupled from the rotational motion of a molecule. The key question of these studies is whether such behavior of the moment of inertia is the manifestation of the super-fluidity of helium and hydrogen at microscopic level. The results are compared to the spectroscopy of molecules and hydrogen clusters in liquid-helium nanodroplets.     

Quasi-static field of an elementary electric dipole in a moving,isotropic, warm plasma

We have investigated the field of an elementary electric dipole in a medium moving at nonrelativistic velocities. We used a quasi-static approximation and a hydrodynamic model of the plasma, taking into account the thermal motion of the electrons. The plasma is assumed to be isotropic, uniform, and infinite. We demonstrate that the intrinsic spatial dispersion of the medium (in the associated reference frame) produces a change in the plasma wave part of the source field.Kirovskii State Teachers Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedeni Radiofizika, No. 10, pp. 1227–1236, October, 1994.     

Direct observation of a cooperative mechanism in the adsorption of heavy metal ions to thiolated surface by in-situ surface plasmon resonance measurements

S-type adsorption kinetics, obtained by surface plasmon resonance spectroscopy measurements, suggest that the rate of Pt2+ adsorption on 1,6-hexanedithiol (HDT) on gold increases until the surface coverage reaches ca. 17%, after which, the adsorption profile of Pt2+ follows Langmuirian behavior for the surface coverage.     

Switchover of the Mechanism between Electron Transfer and Hydrogen‐Atom Transfer for a Protonated Manganese(IV)–Oxo Complex by Changing Only the Reaction Temperature

Hydroxylation of mesitylene by a nonheme manganese(IV)–oxo complex, [(N4Py)Mn^IV(O)]²⁺ ( 1 ), proceeds via one‐step hydrogen‐atom transfer (HAT) with a large deuterium kinetic isotope effect (KIE) of 3.2(3) at 293 K. In contrast, the same reaction with a triflic acid‐bound manganese(IV)‐oxo complex, [(N4Py)Mn^IV(O)]²⁺‐(HOTf)₂ ( 2 ), proceeds via electron transfer (ET) with no KIE at 293 K. Interestingly, when the reaction temperature is lowered to less than 263 K in the reaction of 2 , however, the mechanism changes again from ET to HAT with a large KIE of 2.9(3). Such a switchover of the reaction mechanism from ET to HAT is shown to occur by changing only temperature in the boundary region between ET and HAT pathways when the driving force of ET from toluene derivatives to 2 is around ?0.5 eV. The present results provide a valuable and general guide to predict a switchover of the reaction mechanism from ET to the others, including HAT.     

Catalytic investigation of PtPd and titanium oxide-loaded reduced graphene oxide for enhanced formic acid electrooxidation

Preparation, characterization, and electrocatalytic study of the electrodeposited Pt and Pd (e.g., Pt and PtPd) catalysts on titanium dioxide (TiO₂) modified reduced graphene oxide (rGO) support for formic acid oxidation were performed. The catalyst composites are labeled as xPt/rGO-TiO₂, xPtyPd/rGO-TiO₂, and yPd/rGO-TiO₂ where x and y are cycle numbers of metal electrodeposition (x and y?=?2–6). The characterizations of the catalysts were performed by Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Small and dispersed metal nanoparticles are obtained on rGO-TiO₂. The catalytic performances for formic acid oxidation were measured by cyclic voltammetry (CV) and chronoamperometry (CA). The electrocatalytic results reveal that the bimetallic 4Pt2Pd/rGO-TiO₂ catalyst facilitates formic acid oxidations at the lowest potentials and generates the highest oxidation currents and also improves the highest CO oxidation compared to the monometallic 6Pt/rGO-TiO₂ catalyst. According to the experimental data, the Pd and TiO₂ enhance the electrocatalytic activity of the catalysts towards the formic acid oxidation; the improved catalytic performance of the prepared catalysts strongly relates to the high electrochemically active surface area (ECSA) investigated.

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Graphical abstract TEM image of xPtyPd/rGO-TiO₂ and its CV towards oxidation

     

Growth from Solution,Structure, and Optical Properties of Single-Crystal <Emphasis Type="Italic">para</Emphasis>-Quaterphenyl Films

Samples of single-crystal para-quaterphenyl films up to 8 mm long and 50 μm thick have been obtained for the first time by the solvent?antisolvent growth method. The films have been grown both on the liquid–air interface and in the solution bulk. The morphology, surface quality, and thickness of crystal films have been investigated by the optical, laser confocal, and atomic force microscopies. The structure of the para-quaterphenyl single crystal at room temperature has been refined by X-ray diffraction analysis. The formation and growth mechanisms of crystal films on the liquid–air interface have been discussed. The opticalabsorption and photoluminescence spectra of the solutions and crystal samples have been investigated.     

Growth from Solutions,Structure, and Photoluminescence of Single-Crystal Plates of p-Terphenyl and Its Trimethylsilyl Derivative

Crystallography Reports - Samples of single-crystal plates of p-terphenyl (3Р) and its derivative with terminal substituents–Si(CH3)3 (TMS-3P-TMS), up to 25–30 mm in size and 400...     

Microwave-assisted hydrothermal synthesis of BiOBr/BiOCl flowerlike composites used for photocatalysis

Research on Chemical Intermediates - BiOBr/BiOCl flowerlike composites were successfully synthesized in different solutions containing 0.00–1.50&nbsp;g polyvinylpyrrolidone (PVP) by...