Formation of Complex Organic and Prebiotic Molecules in H2O:NH3:CO2 Ices at Temperatures Relevant to Hot Cores, Protostellar Envelopes, and Planet-Forming Disks.

Photochemistry in H2O:NH3:CO2 cosmic ice analogues was studied at temperatures of 75, 120, and 150 K, relevant to hot cores and warmer regions in protostellar envelopes and planet-forming disks. A combination of two triggers of surface chemistry in cosmic ice analogues, heat and UV irradiation, compared to using either just heat or UV irradiation, leads to a larger variety and an increased production of complex organic molecules, including potential precursors of prebiotic molecules. In addition to complex organic molecules detected in previous studies of H2O:NH3:CO2 ices, ammonium carbamate, carbamic acid, ammonium formate and formamide, we detected acetaldehyde, urea, and, tentatively, glycine, the simplest amino acid. Water ice hampers reactions at low temperature (75 K) but allows the parent molecules, CO2 and NH3, to stay in the solid state and react at higher temperatures (120 and 150 K, above their desorption temperatures). The experiments were performed on the surface of KBr substrates and amorphous silicate grains, analogs of cosmic silicate dust. The production of complex molecules on the silicate surface is decreased compared to KBr. This result suggests that the larger surface area and/or surface properties of the silicate grains play a role in controlling the chemistry, preventing it taking place to the same extent as on the flat KBr substrate. This is further evidence of the fact that cosmic dust grains play an important role in the chemistry taking place on their surface.

Astrochemical Pathways to Complex Organic and Prebiotic Molecules: Experimental Perspectives for In Situ Solid-State Studies.

A deep understanding of the origin of life requires the physical, chemical, and biological study of prebiotic systems and the comprehension of the mechanisms underlying their evolutionary steps. In this context, great attention is paid to the class of interstellar molecules known as "Complex Organic Molecules" (COMs), considered as possible precursors of prebiotic species. Although COMs have already been detected in different astrophysical environments (such as interstellar clouds, protostars, and protoplanetary disks) and in comets, the physical-chemical mechanisms underlying their formation are not yet fully understood. In this framework, a unique contribution comes from laboratory experiments specifically designed to mimic the conditions found in space. We present a review of experimental studies on the formation and evolution of COMs in the solid state, i.e., within ices of astrophysical interest, devoting special attention to the in situ detection and analysis techniques commonly used in laboratory astrochemistry. We discuss their main strengths and weaknesses and provide a perspective view on novel techniques, which may help in overcoming the current experimental challenges.

Two-color surface plasmon resonance nanosizer for gold nanoparticles.

We study the potentialities of a two-color Surface Plasmon Resonance (SPR) spectroscopy nanosizer by monitoring the assembling of a colloidal dispersion of citrate stabilized gold nanoparticles (AuNPs) on SiO2 surface. When the AuNPs/water composite's optical density layer is negligible and the electron mean-free path limitation is taken into account in the AuNPs' dielectric constant;s formulation, the surface density σ of the nanoparticle array and the statistical mean size of the nanoparticles can be straightly determined by using two-color SPR spectroscopy in the context of Maxwell's Garnett theory. The optical method, demonstrated experimentally for AuNPs with a nominal mean diameter of 15 nm, can, theoretically, be extended to bigger nanoparticles, based on a simple scaling relation between the extinction cross section of the single nanoparticle σext and the surface density σ. The experimental results, comparable to those obtained by AFM, transmission electron microscopy and dynamic light scattering technique, establish a novel insight on the SPR spectroscopy's potential to accurately characterize nanomaterials.

Ozone and carbon trioxide synthesis by low energy ion implantation onto solid carbon dioxide and implications to astrochemistry.

Ion implantation experiments were carried out on amorphous (30 K) and crystalline (80 K) solid CO2 using both reactive (D(+), H(+)) and non-reactive (He(+)) ions, simulating different irradiation environments on satellite and dust grain surfaces. Such ion irradiation synthesized several new species in the ice including ozone (O3), carbon trioxide (CO3), and carbon monoxide (CO) the main dissociation product of carbon dioxide. The yield of these products was found to be strongly dependent upon the ion used for irradiation and the sample temperature. Ion implantation changes the chemical composition of the ice with recorded infrared spectra clearly showing the coexistence of D3h and C2v isomers of CO3, for the first time, in ion irradiated CO2 ice.