Large prebiotic molecules in space: photo-physics of acetic acid and its isomers

An increasing number of large molecules have been positively identified in space. Many of these molecules are of biological interest and thus provide insight into prebiotic organic chemistry in the protoplanetary nebula. Among these molecules, acetic acid is of particular importance due to its structural proximity to glycine, the simplest amino acid. We compute electronic and vibrational properties of acetic acid and its isomers, methyl formate and glycolaldehyde, using density functional theory. From computed photo-absorption cross-sections, we obtain the corresponding photo-absorption rates for solar radiation at 1 AU and find them in good agreement with previous estimates. We also discuss glycolaldehyde diffuse emission in Sgr B2(N), as opposite to emissions from methyl formate and acetic acid that appear to be concentrate in the compact region Sgr B2(N-LMH).Comment: 8 pages, 5 figure

Modelling dust extinction in the Magellanic Clouds

We model the extinction profiles observed in the Small and Large Magellanic clouds with a synthetic population of dust grains consisting by core-mantle particles and a collection of free-flying polycyclic aromatic hydrocarbons. All different flavors of the extinction curves observed in the Magellanic Clouds can be described by the present model, that has been previously (successfully) applied to a large sample of diffuse and translucent lines of sight in the Milky Way. We find that in the Magellanic Clouds the extinction produced by classic grains is generally larger than absorption by polycyclic aromatic hydrocarbons. Within this model, the non-linear far-UV rise is accounted for by polycyclic aromatic hydrocarbons, whose presence in turn is always associated to a gap in the size distribution of classical particles. This hints either a physical connection between (e.g., a common cause for) polycyclic aromatic hydrocarbons and the absence of middle-sized dust particles, or the need for an additional component in the model, that can account for the non-linear far-UV rise without contributing to the UV bump at $\sim$217 nm, e.g., nanodiamonds

Modelling extragalactic extinction through gamma-ray burst afterglows

We analyze extragalactic extinction profiles derived through gamma-ray burst afterglows, using a dust model specifically constructed on the assumption that dust grains are not immutable but respond time-dependently to the local physics. Such a model includes core-mantle spherical particles of mixed chemical composition (silicate core, sp2 and sp3 carbonaceous layers), and an additional molecular component, in the form of free-flying polycyclic aromatic hydrocarbons. We fit most of the observed extinction profiles. Failures occur for lines of sight presenting remarkable rises blueward the bump. We find a tendency in the carbon chemical structure to become more aliphatic with the galactic activity, and to some extent with increasing redshifts. Moreover, the contribution of the moleclar component to the total extinction is more important in younger objects. The results of the fitting procedure (either successes and failures) may be naturally interpreted through an evolutionary prescription based on the carbon cycle in the interstellar medium of galaxies

Modelling anharmonic spectra of Polycyclic Aromatic Hydrocarbons at high temperatures

Anharmonicity plays a crucial role in determining the band profile and position of the interstellar Polycyclic Aromatic Hydrocarbons. Here we modeled the infrared spectrum of pyrene (C16H10) using \textrm{ab initio} simulations. We used our new AnharmoniCaOs code to describe the detailed structures of hot band transitions up to moderately high temperatures (600K), using Monte Carlo sampling of the states but beyond that due to high computational cost it is difficult to extend such fancy calculation up to very high temperature relevant for astrophysics. IR spectra of C16H10 beyond 600K was calculated using Density functional based tight binding molecular dynamics simulation. A gradual red shift of the band position and increasing band width is observed with increasing temperatures. The band positions at different temperatures were fitted with a linear regression and the anharmonicity factors were retrieved from the linear fits. Theoretical anharmonicity factors were compared to the recent laboratory results and previous gas phase analyses. This is an extension of a previous project, aimed at completing the calculations to obtain (relatively) high temperature anharmonic vibrational spectra of the pyrene (C16H10) Polycyclic Aromatic Hydrocarbon, using our AnharmoniCaOs code to describe the detailed structures of hot band transitions. We achieved our scientific goal, but the calculation was significantly more demanding than anticipated. The results have been submitted to the Journal of Molecular Spectroscopy by Chakraborty et al., I here describe the technical challenges we faced and the improvements we plan to overcome or mitigate them...

Statica ed estetica. Architetture isodome e bicrome in età nuragica

Nuragic architecture shows itself in a variety of monumental constructions such as nuraghi, sacred wells and springs, and giants’ tombs. In these structures we find common elements and architectural solutions that demonstrate not only that they are expressions of the same culture but also evidence the contemporaneity of the constructive method and style. Some of these employ isodome and pseudo-isodome techniques combined with the use of lithotypes of different colors as a distinct aesthetic. These aspects, well attested to in other nuragic sacred monuments such as wells, are common also in nuraghi. If previously these features were attributed to structural requirements aimed at guaranteeing the stability of the monument, the documentation now demonstrates how the use of this  style and method of construction refers to a clear and explicit aesthetic effect. This fact shows that the function of the nuraghe, sharing the architecture of "sacred" monuments enters into the category of the sacred.L’architettura nuragica si esprime in molteplici forme costruttive attraverso monumenti come i nuraghi, i pozzi, le fonti e le tombe dei giganti. Attraverso la lettura dei modi e degli stili costruttivi si possono riscontrare elementi e soluzioni architettoniche comuni che attestano oltre che la stessa espressione culturale anche la contemporaneità di questi monumenti. Tra queste si evidenziano la tecnica isodoma e la bicromia quest’ ultima risultato dell’accostamento volontario di due o più litotipi differenti nell’apparecchio murario. Tale aspetto, ben attestato nei monumenti di destinazione sacra, quali i pozzi sacri, trova consuetudine anche nel nuraghe. Se precedentemente tali soluzioni erano imputate ad espedienti costruttivi finalizzati a garantire maggiore staticità al monumento, ora la documentazione a riguardo dimostra come l’uso di adoperare sezioni costruttive di colori differenti, sia all’esterno che all’interno dell’edificio sia da riferire ad un chiaro ed esplicito effetto estetico. Questo fatto mette in discussione la funzione dell’edificio nuraghe che condividendo l’architettura del “sacro” entra a far parte anch’esso di tale categoria

VUV photo-processing of PAH cations: quantitative study on the ionization versus fragmentation processes

Interstellar polycyclic aromatic hydrocarbons (PAHs) are strongly affected by the absorption of vacuum ultraviolet (VUV) photons in the interstellar medium (ISM), yet the branching ratio between ionization and fragmentation is poorly studied. This is crucial for the stability and charge state of PAHs in the ISM in different environments, affecting in turn the chemistry, the energy balance, and the contribution of PAHs to the extinction and emission curves. We studied the interaction of PAH cations with VUV photons in the 7-20 eV range from the synchrotron SOLEIL beamline, DESIRS. We recorded by action spectroscopy the relative intensities of photo-fragmentation and photo-ionization for a set of eight PAH cations ranging in size from 14 to 24 carbon atoms, with different structures. At photon energies below ~13.6 eV fragmentation dominates for the smaller species, while for larger species ionization is immediately competitive after the second ionization potential (IP). At higher photon energies, all species behave similarly, the ionization yield gradually increases, leveling off between 0.8 and 0.9 at ~18 eV. Among isomers, PAH structure appears to mainly affect the fragmentation cross section, but not the ionization cross section. We also measured the second IP for all species and the third IP for two of them, all are in good agreement with theoretical ones confirming that PAH cations can be further ionized in the diffuse ISM. Determining actual PAH dication abundances in the ISM will require detailed modeling. Our measured photo-ionization yields for several PAH cations provide a necessary ingredient for such models

Bentonite as a refining agent in waste cooking oils recycling: flash point, density and color evaluation

Clarification of waste recycled cooking oil (WCO) is very important in order to refine the intermediate regenerated base resulting from the previous steps. Bentonite has been historically employed as a filling material for oil refining filters due to its easy availability and its cheap price. In the present communication our early results from the filtration of degummed WCO through a pad of bentonite are presented. In particular, the variation of density, flash point and color have been monitored prior and after the filtration process and compared with samples of non-filtered WCO. An early classification of the bentonite employed has been conducted on the basis of FT-IR and XRD measurements