Destructive adsorption of CCl4 over lanthanum-based solids: linking activity to acid-base properties

The relative activities of a low-surface crystalline and high-surface amorphous LaOCl, further denoted as S1 and S2, have been compared for the destructive adsorption of CCl4. It was found that the intrinsic activity of S2 is higher than that of S1. Both samples were characterized with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N2-physisorption, and Raman and infrared (IR) spectroscopy. IR was used in combination with CO2, CO, and methanol as probe molecules. The CO2 experiments showed that different carbonate species are formed on both materials. For S1, a high surface concentration of bidentate carbonate species and a lower concentration of monodentate carbonate were observed. In the case of S2, bulk carbonates were present together with bridged carbonates. CO adsorption shows that S2 and S1 have very similar Lewis acid sites. However, methanol adsorption experiments showed that S2 had a higher number of stronger Lewis acid sites than S1 and that twofold coordinated methoxy species were more strongly bound than threefold coordinated methoxy species. Because of the analogy between methanol dissociation and the removal of the first chlorine atom in the destructive adsorption of CCl4, the sites enabling twofold coordination were likely to be the same Lewis acid sites actively involved in the destructive adsorption of CCl4. La2O3 was less active than the two LaOCl materials, and therefore, the intrinsic activity of the catalyst increases as the strength of the Lewis acid sites increases. S2 contains more chlorine at the surface than S1, which is expressed by the higher number of sites enabling twofold coordination. Moreover, this explains the difference in destructive adsorption capacity for CCl4 that was observed for the samples S1 and S2. Since LaCl3, being the most acidic phase, is not active for the destructive adsorption of CCl4, basic oxygen atoms, however, remain needed to stabilize the reaction intermediate CCl3 as La-O-CCl3.     

Preliminary investigation to test extragalactic hypothesis for gamma-ray bursts

Summary Recent observations of CGRO satellite challenged the almost universally accepted galactic origin of gamma-ray bursts and have revived the extragalactic, cosmological models. This hypothesis should imply some variations of the morphological and energetic characteristics of the weaker events to which we think the farthest ones might belong. The existence of such variations due to the cosmological red-shift should be tested. In this paper we examine the possible correlations between temporal morphology of the gamma-ray bursts, peak intensity and photon energy spectra when the red-shift effects do not yet occur. We examine the peak intensities and the energy spectral-hardness distributionversus rise times for events observed by previous space missions, with a logN-logS shape free of cosmological effects. The results of this analysis suggest that a wide range of values of the temporal and spectral characteristic parameters is an intrinsic property of the sources. Paper presented at the 6th Cosmic Physics National Conference, Palermo, 3–7 November 1992.     

EXAFS and XANES Structure determination of Mn2+ binding in ATP complexes

Summary The binding of Mn²⁺ ions to ATP molecules has been studied by means of the fine-structure analysis of X-ray absorption spectra (EXAFS and XANES) at theK-edge of Mn using the synchrotron, radiation facility PULS in Frascati. The results obtained in both freeze-dried and liquid samples of aqueous solutions at room temperature of the Mn-ATP complex under diffrent values ofpH and Mn:ATP ratio are reported and discussed. The Mn²⁺ ion appears to be octahedrally coordinated, the phosphate oxygen atoms being in the first co-ordination shell. Values of (2.15±0.05) ? and (3.4±0.05) ?, respectively, have been found for Mn-O and Mn-P distances. Theoretical considerations together with experimental results do not support the existence of a direct binding of the Mn to the N(7) atom of the adenine ring. The coordination numbers for the first and second shell are consistent with the formation of a Mn(ATP)₂ complex in solution atpH=9 and Mn: ATP=1:10, while a Mn-ATP 1:1 complex is found at lowerpH and higher Mn: ATP ratios. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Possible implications of the channeling effect in NaI(Tl) crystals

The channeling effect of low energy ions along the crystallographic axes and planes of NaI(Tl) crystals is discussed in the framework of corollary investigations on WIMP dark matter candidates. In fact, the modeling of this existing effect implies a more complex evaluation of the luminosity yield for low energy recoiling Na and I ions. In the present paper related phenomenological arguments are developed and possible implications are discussed at some extent. PACS 95.35.+d     

An analysis of the morphological and spectral behaviour of the gamma-ray bursts

Summary We investigate by a statistical analysis possible correlations among the observational parameters of the γ-ray bursts: the rise time, the decay time and spectral hardness. We discuss the physical constraints implied by the results. To speed up publication, the proofs were not sent to the authors and were supervised by the Scientific Committee.     

Halo-carbonyl complexes of palladium,platinum and gold

In this review we summarize some recent literature data concerning synthetic procedures, properties, structure, reactivity and applications of halo-carbonyl complexes of palladium, platinum and gold, taking into consideration that the organometallic chemistry of these metals, with a particular attention to the halo-carbonyls, has been reviewed 20 years ago [F. Calderazzo, J. Organomet. Chem. 400 (1990) 303]. A brief overview of the early studies is provided.     

On a further search for a yearly modulation of the rate in particle Dark Matter direct search

The results achieved with a statistics of 14962 kg·day, collected with the large mass highly radiopure DAMA NaI(Tl) set-up, are described and investigated in terms of WIMP annual modulation signature. A maximum likelihood analysis of these data, combined with the statistics of 4549 kg·day previously published (total statistics of 19511 kg·day), favours the hypothesis of presence of an annual modulation at 99.6% C.L.     

Identifying a “dark matter” signal by nonisotropic scintillation detector

Summary In this note we investigate the possibility to identify a “dark matter” signal by means of low-background anisotropic scintillators.     

A variational principle for the dynamic problem of linear coupled thermoelasticity

Summary A functional is constructed by whose stationarity the mixed problem for linear and dynamic thermoelasticity is obtained. In contrast with previous results[2], [4], [8], neither constrained variations nor previous transformations upon the equations of the problem are used. The unrestricted variational formulation is made possible by means of a convolutive bilinear form.

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Sommario Si costruisce un funzionale dalla cui stazionarietà si ricava il problema misto della termoelasticità lineare accoppiata. A differenza di precedenti risultati[2], [4], [8] non si ricorre né a variazioni bloccate né a preliminari trasformazioni del problema. La formulazione variazionale non ristretta è resa possibile dall'uso di una forma bilineare convolutiva.

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Work done in the sphere of activity of the Group for Mathematical Research of the (Italian) C.N.R.     

Bent dinuclear platinum(II) halo-bridged carbonyl complexes

Crystals of trans-Pt?(μ-X)?X?(CO)? (X = Br, I) have been grown and their molecular and crystalline structures have been solved by X-ray diffraction methods. In both cases the dinuclear molecules are bent, with a bending angle of 164.6° and 156.5° for the bromide and the iodide, respectively. While the structure of the bromo-derivative is reported here for the first time, a modification of trans-Pt?(μ-I)?I?(CO)? with planar centrosymmetric molecules is known. This appears to be a rare case of a platinum(II) halo-bridged derivative structurally characterized in both bent and planar forms.