Vittorio Bariosco

Water and methanol are key components of interstellar ices and gas in star- and planet-forming regions, but direct observations of water in low-mass protostars are challenging due to atmospheric absorption. We present high-resolution ( R = 70,500) mid-infrared spectroscopy of the class I protostar SVS13-A with EXES on board SOFIA at 26 μ m, targeting both H ₂ O and CH ₃ OH absorption lines. Several lines of each species are detected, tracing warm gas with rotational temperatures of ∼140–170 K. Remarkably, the methanol column density is a factor of ∼4 higher than that of water, well above typical interstellar ice ratios (3 OH/H ₂ O ratio may reflect selective sublimation due to the distribution of binding energies or ice stratification in the inner envelope. These observations probe the inner regions of the protostar, where planets are expected to form and inherit the chemical composition of their natal environment, providing a direct link between ice sublimation and gas-phase chemistry. Our results represent the first high-spectral-resolution mid-infrared view of both water and methanol toward a low-mass protostar, offering a unique window into the chemical composition of the innermost envelope and planet-forming region and highlighting the diagnostic power of high-resolution mid-infrared spectroscopy to uncover hidden chemical layers and the ice-to-gas transition in embedded protostars.

Recent studies have highlighted the biological significance of 8-hydroxyquinoline-2-carboxylic acid (8-HQA) as a metal chelator. In this work, several techniques were applied for the study of the interaction of 8-HQA with vanadium(IV/V) oxidometal ions at a temperature of T = 298.2 K and an ionic strength of I = 0.20 mol dm^-3 in KCl_(aq). The redox behavior of the chemical system was defined, and the stability constants of the formed complexes were determined by H⁺-ion selective electrode potentiometry and UV-vis spectrophotometric titrations, while nuclear magnetic resonance (NMR) and electron spin resonance (ESR) spectroscopies and mass spectrometry provided stoichiometric and structural information. The formation of both oxidovanadium(IV) and dioxidovanadium(V) ML complexes with 8-HQA was observed in aqueous solution, with both complexes being particularly stable in acidic conditions. The dioxidovanadium(V) compound is stable even at neutral pH, but dimeric or tetrameric hydrolytic species are predominant under alkaline conditions. In contrast, oxidovanadium(IV) complexes undergo oxidation as the pH increases. Nevertheless, under strictly anaerobic conditions, the complexation of oxidovanadium(IV) by 8-HQA can also occur at pH > 6.0. The nature of the oxidovanadium(IV) and dioxidovanadium(V) ML complexes, representing the major species formed in solution, was further investigated by DFT calculations.

Understanding diffusion on interstellar ices is key to modeling the chemical evolution of cold molecular clouds, where low temperatures severely limit molecular mobility. In this study, we introduce a robust and fully automated multiscale computational framework to quantify diffusion processes of adsorbates at the surface of amorphous solid water (ASW). Using H₂S as a test case, whose binding sites were previously studied at the ab initio level, we constructed a detailed network of 141 adsorption sites connected by over 270 transition states. All density functional energetics were benchmarked against DLPNO–CCSD­(T), achieving chemical accuracy in the description of diffusion barriers, which span from 0.1 to 27 kJ mol^–1 with a median value of 5.4 kJ mol^–1. An off-lattice kinetic Monte Carlo (kMC) model adopting both the ab initio diffusion barriers and binding energies for the desorption processes was carried out to compute temperature-dependent diffusion coefficients and to reconstruct the temperature-programmed desorption (TPD) curve. Our simulations reveal that thermal diffusion of H₂S is negligible below 20 K, with diffusion coefficients as low as 10^–48 cm² s^–1 at 10 K, thus excluding Langmuir–Hinshelwood surface encounters under typical dense cloud conditions. Moreover, under submonolayer conditions, diffusion was found to have negligible influence on the reconstructed TPD peak position. Furthermore, our results demonstrate that a universal scaling factor f to guess the diffusion barriers (ΔE _diff) from the sole knowledge of BE: f = ΔE _diff/BE does not apply as it exhibits wide variability across the sampled configurations. These findings highlight the need for incorporating statistically meaningful distributions of binding energies and diffusion barriers in astrochemical models to more accurately capture diffusion and surface reactivity on interstellar ices.

The luminosity of embedded protostars is commonly measured via observations of the dust continuum spectral energy distribution from millimetre to infrared wavelengths. However, this method cannot be applied to embedded protostars in binary or multiple systems, where their components are usually unresolved over this extended wavelength range. We propose a new method, based on the idea that a molecule formed (mainly) on the grain surfaces only emits lines in the region where it thermally sublimates from the grain mantles, heated by the photons emitted by the embedded source. In this respect, carbonyl sulfide (OCS) is an optimal molecule, because of its low binding energy and rotational lines in the millimetre. We apply the method to the protobinary system NGC1333 IRAS4A, using ALMA high-spatial resolution (∼50 au) observations of the OCS(19-18) line as part of the ALMA Large Program FAUST. We also present new quantum mechanics calculations of the OCS binding energy distribution, essential for the application of the method. We found that the two binary components, A1 and A2, have a comparable luminosity within the error bars, 7.5±2.5 and 7±1 L⊙, respectively. We discuss the reliability of the estimated luminosities and the potential of this new method for measuring the luminosity of embedded protostars in binary and multiple systems.

Temperature programmed desorption (TPD) is a well-known technique to study gas-surface processes, and it is characterized by two main quantities: the adsorbate binding energy and the pre-exponential factor. While the former has been well addressed in recent years by both experimental and computational methods, the latter remains somewhat ill-defined, and different schemes have been proposed in the literature for its evaluation. In the astrochemistry context, binding energies and pre-exponential factors are key parameters that enter microkinetic models for studying the evolution over time of the chemical species in the universe. In this paper, we studied, by computer simulations, the effect of different pre-exponential factor models using water, ammonia, and methanol adsorbed on amorphous and crystalline ices as test cases: specifically, the one most widely used by the astrochemical community (Herbst–Hasegawa), the models provided by Tait and Campbell, and an extension of the Tait formulation including the calculation of the vibrational partition function. We suggest the methods proposed by Tait and Campbell that provide TPD temperature peaks within 30 K of each other while avoiding demanding quantum mechanical calculations, as they are based on tabulated data. Finally, when the explicit inclusion of the vibrational partition function is needed, we propose a cost-effective strategy to include all the thermal contributions in the partition functions without the need for performing a full vibrational calculation of the whole system.

Methanol (CH$_3$OH) is the simplest and most abundant interstellar complex organic molecule (iCOM) observed in warm and cold environments. It is thought to be formed on the surfaces of dust grains and released into the gas-phase by thermal desorption of the ices in the warm regions where the dust temperature is high ($\ge$100 K). However, the presence of gaseous methanol in cold environments represented a challenge since its detection, e.g. in cold molecular clouds, prestellar cores, and protoplanetary discs. The reason is that thermal desorption was thought to be completely inefficient in these conditions. In this work, we show that this is not the case. Specifically, we present new calculations of the binding energy (BE) distribution on an iced grain composed of 200 water molecules. On this grain we obtained 223 unique sites with different BE. We found that the methanol BE distribution is well reproduced by a Gaussian function with a mean of 35.5 kJ mol−1 (4255 K) and a standard deviation of 13.0 kJ mol−1 (1558 K). To facilitate the incorporation of our calculations into astrochemical models, we provide a table with the fraction of sites as a function of the BE and the corresponding prefactors. Comparison with published experimental BE values suggests that they are dominated by the larger BE sites. Finally, and most importantly, our calculations show that 2 per cent of the BEs are around 10 kJ mol−1 (1240 K), implying that thermal desorption from these sites may explain the presence of gaseous methanol in cold environments.

Despite hydrogen sulphide (H₂S) has been predicted to be the major reservoir of S-bearing species on the icy mantles of interstellar grains, no solid H₂S has been detected so far. A crucial parameter that governs whether or not a species remains frozen on to the grain mantles is its binding energy (BE). We present a new computational study of the H₂S BE on a large amorphous water ice surface, constituted by 200 water molecules. The resulting H₂S BE distribution ranges from 57 K (0.5 kJ mol⁻¹) to 2406 K (20.0 kJ mol⁻¹), with the average μ = 984 K (8.2 kJ mol⁻¹). We discuss the reasons why the low bound of the newly computed BE distribution, which testifies to the very weak interaction of H₂S with the ice surface, has never been found by previous theoretical or experimental works before. In addition, the low H₂S BEs may also explain why frozen H₂S is not detected in interstellar ices. Following previous molecular dynamics studies that show that the energy of reactions occurring on ice surfaces is quickly absorbed by the water molecules of the ice and conservatively assuming that 10 per cent of the HS + H → H₂S formation energy (−369.5 kJ mol⁻¹) is left to the newly formed H₂S, its energy is more than twice the largest BE and five times the average BE and, hence, H₂S will most likely leave the water surface.