Microscopic structure and properties of an interface between coexisting phases of an associating fluid adsorbed in slitlike pores

Using density functional theory, we calculate density profiles of an associating fluid in slitlike pores. These profiles characterize an interface between two coexisting, adsorbed phases, e.g., between gaseous and liquid phases formed during capillary condensation. Our study has been carried out for weakly, as well as for strongly, associated fluids confined in pores of different widths. We also investigate the role of the fluid-wall interaction.     

The adsorption of a hard sphere fluid in a slit-like pore filled with a disordered matrix of hard spheres: attractive wall-hard sphere interaction

The adsorption of a hard sphere fluid in a slit-like pore filled with a disordered hard sphere matrix is studied using the inhomogeneous Ornstein-Zernike equation with hypernetted chain closure. In contrast to previous studies, an attractive wall-hard sphere interaction is considered. The adsorption is affected by the attractive interaction both directly by the fluid-wall interaction and indirectly by the change in the structure of the matrix. Density profiles and pair distribution functions are reported. For comparison, grand canonical Monte Carlo simulation data are obtained. The agreement of the theoretical and simulation results is satisfactory but somewhat less pleasing than for the purely repulsive case.     

New measurements and global analysis of rotational spectra of Cl-, Br-, and I-benzene: Spectroscopic constants and electric dipole moments

The data available from rotational spectroscopy for chlorobenzene, bromobenzene, and iodobenzene have been extended by new measurements in the mm-wave region and in supersonic expansion in the cm-wave region. All available ground state measurements have been combined in global fits to derive precise rotational, centrifugal, and nuclear quadrupole coupling constants for the molecules. Rotational transitions in first excited states of the lowest frequency normal modes in bromobenzene and iodobenzene have been assigned and fitted. The values of electric dipole moments for ³⁵Cl-, ⁷⁹Br-, ⁸¹Br-, and I-benzene have been determined from Stark effect measurements on selected hyperfine components in the supersonic expansion spectrum, and are compared with values for several other series of monohalogen molecules.     

Colloidal Systems on the Basis of Novel Reactive Surfmers

Summary: New anion surfmers of the family of maleic acid asymmetrical esters have been synthesized. Some of its features in the process of emulsion copolymerization with styrene have been studied. The characteristics of covering, obtained on the basis of such latexes of new generation have been investigated as well.     

A Grassmannian band method approach to the Nehari-Takagi problem

The band method is a flexible method for solving a variety of interpolation and extension problems which has evolved into increasing levels of sophistication over the past two decades. This article enhances the Grassmannian version of the band method to handle the Nehari-Takagi problem rather than merely the Nehari problem.     

Different faces of chaos in FRW models with scalar fields—geometrical point of view

FRW cosmologies with conformally coupled scalar fields are investigated in a geometrical way by the means of geodesics of the Jacobi metric. In this model of dynamics, trajectories in the configuration space are represented by geodesics. Because of the singular nature of the Jacobi metric on the boundary set of the domain of admissible motion, the geodesics change the cone sectors several times (or an infinite number of times) in the neighborhood of the singular set .

We show that this singular set contains interesting information about the dynamical complexity of the model. Firstly, this set can be used as a Poincaré surface for construction of Poincaré sections, and the trajectories then have the recurrence property. We also investigate the distribution of the intersection points. Secondly, the full classification of periodic orbits in the configuration space is performed and existence of UPO is demonstrated. Our general conclusion is that, although the presented model leads to several complications, like divergence of curvature invariants as a measure of sensitive dependence on initial conditions, some global results can be obtained and some additional physical insight is gained from using the conformal Jacobi metric. We also study the complex behavior of trajectories in terms of symbolic dynamics.     

A primitive model for hexamethylpararosaniline (crystal violet) monomolecular adlayer: a Monte Carlo simulation study

The NVT Monte Carlo simulation results are reported for a model of two-dimensional (2D) chemically associating fluid with six attractive sites per monomer disc. Three of these sites are of the type α and the other three of the type β. The sites α and β are fixed inside a hard core, they follow each other anticlockwise, with a `valence' angle of 60°. It is assumed that only α+β site–site association of two different discs occurs. Complex formation, dependent on the density and association energy, is much more sophisticated, in comparison to previously studied models of dimerizing and polymerizing discs. An analysis of complexes in terms of the fractions of singly, doubly,…, hexa-bonded particles is performed, and the dimensions and distributions of complexes are studied. We obtained the pair distribution functions of particles and structure factor in the fluid layer. The model was inspired by experiments on visualization of organic monolayers in the framework of scanning tunneling microscopy (STM). Currently it yields a preliminary insight into the molecular organization of crystal violet molecules on the iodine covered (111) single-crystal surface plane observed experimentally. Extensions of the model and methodology are discussed.     

Comprehensive analysis of the FASSST rotational spectrum of S(CN)2

Results are reported of a comprehensive investigation of an almost continuous rotational spectrum of S(CN)₂ recorded over the frequency region 110-374 GHz by means of the FASSST spectroscopic technique. The spectrum was analysed in detail and over 22 000 transitions were assigned in total. Precise, octic order spectroscopic constants in the asymmetric rotor Hamiltonian have been determined for the ground state and 12 different vibrationally excited states of the parent isotopologue, including first excited states of five different normal modes. Three states near 370 cm⁻¹ and four states near 490 cm⁻¹ above the ground state were found to be mutually interacting and were successfully analysed in terms of a triad and a tetrad of coupled states, respectively. Rotational transitions in the ³⁴S, ¹³C, and ¹⁵N isotopologues of S(CN)₂ have also been assigned and fitted, and newly determined rotational constants were used to derive the geometry of the molecule. The complex multistate analysis of the spectrum was carried out with the newly developed AABS software package for Assignment and Analysis of Broadband Spectra.     

Reforming of oxygenates for H2 production: correlating reactivity of ethylene glycol and ethanol on Pt(111) and Ni/Pt(111) with surface d-band center

The dehydrogenation and decarbonylation of ethylene glycol and ethanol were studied using temperature programmed desorption (TPD) on Pt(111) and Ni/Pt(111) bimetallic surfaces, as probe reactions for the reforming of oxygenates for the production of H2 for fuel cells. Ethylene glycol reacted via dehydrogenation to form CO and H2, corresponding to the desired reforming reaction, and via total decomposition to produce C(ad), O(ad), and H2. Ethanol reacted by three reaction pathways, dehydrogenation, decarbonylation, and total decomposition, producing CO, H2, CH4, C(ad), and O(ad). Surfaces prepared by deposition of a monolayer of Ni on Pt(111) at 300 K, designated Ni-Pt-Pt(111), displayed increased reforming activity compared to Pt(111), subsurface monolayer Pt-Ni-Pt(111), and thick Ni/Pt(111). Reforming activity was correlated with the d-band center of the surfaces and displayed a linear trend for both ethylene glycol and ethanol, with activity increasing as the surface d-band center moved closer to the Fermi level. This trend was opposite to that previously observed for hydrogenation reactions, where increased activity occurred on subsurface monolayers as the d-band center shifted away from the Fermi level. Extrapolation of the correlation between activity and the surface d-band center of bimetallic systems may provide useful predictions for the selection and rational design of bimetallic catalysts for the reforming of oxygenates.     

Experimental and theoretical study of reactivity trends for methanol on Co/Pt(111) and Ni/Pt(111) bimetallic surfaces

Methanol was used as a probe molecule to examine the reforming activity of oxygenates on NiPt(111) and CoPt(111) bimetallic surfaces, utilizing density functional theory (DFT) modeling, temperature-programmed desorption, and high-resolution electron energy loss spectroscopy (HREELS). DFT results revealed a correlation between the methanol and methoxy binding energies and the surface d-band center of various NiPt(111) and CoPt(111) bimetallic surfaces. Consistent with DFT predictions, increased production of H2 and CO from methanol was observed on a Ni surface monolayer on Pt(111), designated as Ni-Pt-Pt(111), as compared to the subsurface monolayer Pt-Ni-Pt(111) surface. HREELS was used to verify the presence and subsequent decomposition of methoxy intermediates on NiPt(111) and CoPt(111) bimetallic surfaces. On Ni-Pt-Pt(111) the methoxy species decomposed to a formaldehyde intermediate below 300 K; this species reacted at approximately 300 K to form CO and H2. On Co-Pt-Pt(111), methoxy was stable up to approximately 350 K and decomposed to form CO and H2. Overall, trends in methanol reactivity on NiPt(111) bimetallic surfaces were similar to those previously determined for ethanol and ethylene glycol.