Destruction of dimethyl ether and methyl formate by collisions with He+^+

To correctly model the abundances of interstellar complex organic molecules (iCOMS) in different environments, both formation and destruction routes should be appropriately accounted for. While several scenarios have been explored for the formation of iCOMs via grain and gas-phase processes, much less work has been devoted to understanding the relevant destruction pathways, with special reference to (dissociative) charge exchange or proton transfer reactions with abundant atomic and molecular ions such as He$^+$, H$_3^+$ and HCO$^+$. By using a combined experimental and theoretical methodology we provide new values for the rate coefficients and branching ratios (BRs) of the reactions of He$^+$ ions with two important iCOMs, namely dimethyl ether (DME) and methyl formate (MF). We also review the destruction routes of DME and MF by other two abundant ions, namely H$_3^+$ and HCO$^+$. Based on our recent laboratory measurements of cross sections and BRs for the DME/MF + He$^+$ reactions over a wide collision energy range, we extend our theoretical insights on the selectivity of the microscopic dynamics to calculate the rate coefficients $k(T)$ in the temperature range from 10 to 298 K. We implement these new and revised kinetic data in a general model of cold and warm gas, simulating environments where DME and MF have been detected. Due to stereodynamical effects present at low collision energies, the rate coefficients, BRs and temperature dependences here proposed differ substantially from those reported in KIDA and UDfA, two of the most widely used astrochemical databases. These revised rates impact the predicted abundances of DME and MF, with variations up to 40% in cold gases and physical conditions similar to those present in prestellar coresComment: accepted for publication in Astronomy and Astrophysics (manuscript no. AA/2018/34585), 10 pages, 3 figure

Testing the Debye Function Approach on a Laboratory X-ray Powder Diffraction Equipment. A Critical Study

Total Scattering Methods are nowadays widely used for the characterization of defective and nanosized materials. They commonly rely on highly accurate neutron and synchrotron diffraction data collected at dedicated beamlines. Here, we compare the results obtained on conventional laboratory equipment and synchrotron radiation when adopting the Debye Function Analysis method on a simple nanocrystalline material (a synthetic iron oxide with average particle size near to 10nm). Such comparison, which includes the cubic lattice parameter, the sample stoichiometry and the microstructural (size-distribution) analyses, highlights the limitations, but also some strengthening points, of dealing with conventional powder diffraction data collections on nanocrystalline material

Roadmap on dynamics of molecules and clusters in the gas phase

This roadmap article highlights recent advances, challenges and future prospects in studies of the dynamics of molecules and clusters in the gas phase. It comprises nineteen contributions by scientists with leading expertise in complementary experimental and theoretical techniques to probe the dynamics on timescales spanning twenty order of magnitudes, from attoseconds to minutes and beyond, and for systems ranging in complexity from the smallest (diatomic) molecules to clusters and nanoparticles. Combining some of these techniques opens up new avenues to unravel hitherto unexplored reaction pathways and mechanisms, and to establish their significance in, e.g. radiotherapy and radiation damage on the nanoscale, astrophysics, astrochemistry and atmospheric science

Materiali fotoattivi nanostrutturati: sintesi, caratterizzazioni e applicazioni.

Titanium dioxide is suitable to answer some important needs of our society, particularly in the environmental field, as a photo catalyst, and in the energy field, for realization of devices for a rational use of solar energy. Thanks to nanotechnology, this material has found a renewed interest by the scientific community for innovative properties that occur as a result of its nanoscale. The materials based on titanium dioxide produced in this work were obtained by sol-gel method, which is now one of the most studied techniques for the synthesis of nanostructured materials. The interest stimulated by this method is its extreme versatility and advantages of ease of control of process parameters. Specifically, samples were synthesized containing either only titanium dioxide, or inorganic hybrid silica / titania. The reasons that led to the trial presented here lie in understanding the influence of experimental parameters (composition, temperature, time) that govern the synthesis process on nature and structural characteristics of the material isolated. Morphology, crystallinity and micro-structure, have been investigated by X-ray Powder Diffraction (XRPD), Nitrogen Physisorption, Atomic Force Microscope (AFM) and Debye Function Analysis (DFA). We also correlated the effect of experimental and structural aspects on the functional properties (photocatalytic activity) of the synthesized materials. Another important aspect of this work concerns the investigation of the application of the materials produced for the surface modification of textile substrates (polyester) in order to obtain "smart textiles" that can effectively reduce environmental pollutants. In this area we investigated the effects of variation of process parameters on the performance exhibited by functionalized textiles

L'attivita' economica pubblica e la concorrenza: profili applicativi degli articoli 90 del Trattato di Roma ed 8 della Legge 287/90

Dottorato di ricerca in diritto dell'economia. 6. ciclo. Tutore C. AngeliciConsiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7, Rome; Biblioteca Nazionale Centrale - P.za Cavalleggeri, 1, Florence / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

Dissociative charge transfer of organic molecules induced by collisions with the He+ cation. A joint experimental and theoretical study of relevance for the interstellar medium evolution

Collisions with He+ are an important pathway for the destruction of complex organic molecules in the interstellar medium (ISM). We have carried out dissociative charge transfer reactions of He+ with two oxygen containing organic molecules, ubiquitous in ISM: dimethyl ether (DME, CH3OCH3 ) and methyl formate (MF, HCOOCH3). Since they have a prebiotic relevance, several models were developed to explain how these molecules are formed and destroyed in the ISM. The reactions have been investigated by using the home-built Guided-Ion Beam Mass Spectrometer (GIB-MS) apparatus. Absolute cross sections and branching ratios of the products have been measured as a function of the collision energy in the hyperthermal energy range (i.e. from about 0.1 eV to 7 eV). The presence of the molecular ion was not observed among the products for these reactions, which means that the nascent DME and MF radical cations are formed in a dissociative state. Insights on both the charge transfer processes have been obtained by investigating the nature of the non-adiabatic transitions between the reactant and product potential energy surfaces (PES). The PES has been represented by using a semi-empirical method to model the inter-molecular interactions. To explain the experimental evidence, two excited states of DME and MF radical cations have been invoked: He+ captures an electron from inner valence orbitals of both the organic molecules, having binding energies ~10 eV higher than the HOMO. An improved Landau-Zener-Stückelberg model has been developed to obtain the total integral cross-section to be compared with the experimental results. Inter-molecular interaction and electron densities of the orbitals involved in the reaction turned out to be key points to describe the dynamics of the two studied dissociative charge transfers. A very good agreement is obtained between the experimental and calculated total cross-sections at low collision energy, which is the most relevant range for the interstellar environment. These results represent a significant starting point to estimate rate constants for the total dissociation of DME and MF by collisions with He+ ions in the ISM at low temperatures

Expanding the Use of Peroxygenase from Oat Flour in Organic Synthesis: Enantioselective Oxidation of Sulfides

Biocatalyzed oxidations are an important target in sustainable synthesis since chemical oxidations often require harsh conditions and metal-based catalysts. A raw peroxygenase-containing enzymatic preparation from oat flour was tested as a biocatalyst for the enantioselective oxidation of sulfides to sulfoxides and the variations of some reaction parameters were evaluated. Under optimal conditions, thioanisole was fully converted into the corresponding (R)-sulfoxide with high optical purity (80% ee) and the same stereopreference was maintained in the oxidation of some other sulfides. Changes in the substituent on the sulfur atom affected the selectivity of the enzyme and the best results were obtained with phenyl methoxymethyl sulfide, which gave the corresponding sulfoxide in 92% ee as exclusive product. The over-oxidation of sulfides to sulfones was instead detected in all the other cases and preferential oxidation of the (S)-enantiomer of the sulfoxide intermediate was observed, albeit with low selectivity. Carrying out the oxidation of thioanisole up to the 29% formation of sulfone led to enhancement of the sulfoxide optical purity (89% ee). The activity in sulfoxidation reactions, in addition to that reported in the epoxidation of different substrates, makes this plant peroxygenase a promising and useful tool in organic synthesis