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In this work, we analyse soft X-ray emission due to mass accretion on to compact stars and its effects on the time-scale to reach chemical equilibrium of eventual surrounding astrophysical ices exposed to that radiation. Reaction time-scales due to soft X-ray in water-rich and pure ices of methanol, acetone, acetonitrile, formic acid, and acetic acid were determined. For accretion rates in the range $\dot{m}=10^{-12}\!-\!10^{-8}\,{\rm M}_\odot$ yr−1 and distances in the range 1–3 LY from the central compact objects, the time-scales lie in the range 10–108 yr, with shorter time-scales corresponding to higher accretion rates. Obtained time-scales for ices at snow-line distances can be small when compared to the lifetime (or age) of the compact stars, showing that chemical equilibrium could have been achieved. Time-scales for ices to reach chemical equilibrium depend on X-ray flux and, hence, on accretion rate, which indicates that systems with low accretion rates may not have reached chemical equilibrium.

In this study, we employed broadband X-rays ($6-2000$ eV) to irradiate the frozen acetone CH$_3$COCH$_3$, at the temperature of 12 K, with different photon fluences up to $2.7\times 10^{18}$ photons cm$^{-2}$. Here, we consider acetone as a representative complex organic molecule (COM) present on interstellar ice grains. The experiments were conduced at the Brazilian synchrotron facility (LNLS/CNPEN) employing infrared spectroscopy (FTIR) to monitor chemical changes induced by radiation in the ice sample. We determined the effective destruction cross-section of the acetone molecule and the effective formation cross-section for daughter species. Chemical equilibrium, obtained for fluence $2\times 10^{18}$ photons cm$^{-2}$, and molecular abundances at this stage were determined, which also includes the estimates for the abundance of unknown molecules, produced but not detected, in the ice. Timescales for ices, at hypothetical snow line distances, to reach chemical equilibrium around several compact and main-sequence X-ray sources are given. We estimate timescales of 18 days, 3.6 and 1.8 months, $1.4\times 10^9-6\times 10^{11}$ years, 600 and $1.2\times 10^7$ years, and $10^7$ years, for the Sun at 5 AU, for O/B stars at 5 AU, for white dwarfs at 1 LY, for the Crab pulsar at 2.25 LY, for Vela pulsar at 2.25 LY, and for Sagittarius A* at 3 LY, respectively. This study improves our current understanding about radiation effects on the chemistry of frozen material, in particular, focusing for the first time, the effects of X-rays produced by compact objects in their eventual surrounding ices., Comment: Accepted in MNRAS. This is a preprint. 14 pages, 7 figures

The processing of H2O:CO2:CH4 (10:1:1) and H2O:CO2:CH4:NH3 (10:1:1:1) ices at 72 K by oxygen ions was studied in an attempt to simulate the physicochemical effects induced by energetic ions on the surface of Enceladus (or similar cold surfaces in the outer Solar System). The experiments were carried out at the Grand Accélérateur National d’Ions Lourds (GANIL) in Caen/France. The samples were irradiated with 15.7-MeV O5+ at the IRRadiation SUD (IRRSUD) beamline and with 108-keV O6+ at the Accélérateurs pour les Recherches avec les Ions de Basses Energies (ARIBE) beamline. The frozen samples were monitored by Fourier Transform Infrared Spectroscopy (FTIR) spectroscopy (4000–650 cm−1, 2.5–15.4 μm, at 1 cm−1 resolution). The identified molecular species formed during irradiation were CO, OCN−, CH3OH, HCN, CN−, H2CO3, HNCO, HCO and CO3. The effective formation cross-sections for the synthesis of new species and the effective molecular destruction cross-sections of the parent species in the experiments with MeV ions were found to be of the order of 10−14–10−13 cm2. For the keV ion experiments, these values were of the order of 10−16–10−15 cm2. The fluence at which the sample reaches chemical equilibrium and the molecular abundances in this region (equilibrium branching ratios) were estimated. These experiments suggest that the chemical inventory on the surface of Enceladus can be influenced by the incidence of charged particles on to the moon’s surface.

The physical evolution of Young Stellar Objects (YSOs) is accompanied by an enrichment of the molecular complexity, mainly triggered by the heating and energetic processing of the astrophysical ices. In this paper, a study of how the ice column density varies across the protostellar evolution has been performed. Tabulated data of H$_2$O, CO$_2$, CH$_3$OH, HCOOH observed by ground- and space-based telescopes toward 27 early-stage YSOs were taken from the literature. The observational data shows that ice column density and spectral index ($\alpha$), used to classify the evolutionary stage, are well correlated. A 2D continuum radiative transfer simulation containing bare and grains covered by ices at different levels of cosmic-ray processing were used to calculate the Spectral Energy Distributions (SEDs) in different angle inclinations between face-on and edge-on configuration. The H$_2$O:CO$_2$ ice mixture was used to address the H$_2$O and CO$_2$ column density variation whereas the CH$_3$OH and HCOOH are a byproduct of the virgin ice after the energetic processing. The simulated spectra were used to calculate the ice column densities of YSOs in an evolutionary sequence. As a result, the models show that the ice column density variation of HCOOH with $\alpha$ can be justified by the envelope dissipation and ice energetic processing. On the other hand, the ice column densities are mostly overestimated in the cases of H$_2$O, CO$_2$ and CH$_3$OH, even though the physical and cosmic-ray processing effects are taken into account., Comment: Accepted for publication in The Astrophysical Journal. 29 pages, 16 figures

The survival of astrophysical ices in the star-forming regions depends on the suitability of temperature, density and radiation conditions. In this paper, the role of Interstellar Radiation Field (ISRF) on ices in Elias 29 is addressed. This object is the most luminous protostar in $\rho$ Oph E molecular cloud, and is surrounded by many Young Stellar Objects distant only a few arcminutes. In addition, other two brightness BV stars (S1 and HD 147889) enhance the external irradiation in Elias 29. This study was carried out by using the Monte Carlo radiative transfer code RADMC-3D assuming an internal and external irradiation. As result, we found that HD 147889 dominates the ISRF, instead of the closest protostars, and contributes to enhance the external irradiation in 44 times the standard value. Furthermore, remarkable effects are observed in FIR spectrum, as well as in near-IR image. Additionally, the snowline positions of volatile compounds, such as CO, O$_2$, N$_2$ and CH$_4$ are redefined to a toroidal-shaped morphology in the envelope, with low FUV flux (10$^{-7}$ ergs cm$^{-2}$ s$^{-1}$). In such scenario, the formation of complex molecules as result of hydrogenation or oxygenation of volatile species are expected to be severely affected.

Molecular clouds (MCs) are exposed to Galactic and extragalactic cosmic rays (CR) that trigger several physical and physicochemical changes, including gas and grain heating and molecular destruction and formation. Here we present a theoretical model describing the energy delivered by CRs, composed of protons, alphas, and electrons taken from Voyager I measurements, into a typical MC with 5400 M ☉ (composed mainly of H with a density law of r −1.2) and size around 1 × 106 au. The calculation was performed employing the Monte Carlo toolkit GEANT4 to obtain the energy deposition per mass from several types of secondary particles (considering nuclear and hadron physics). The results indicate that incoming protons contribute to most of the energy delivered in the MC in all regions (maximum ∼230 MeV g−1 s−1 at outer regions of the cloud). Secondary electrons are the second most important component for energy deposition in almost all layers of the MC and can deliver an energy rate of ∼130 MeV g−1 s−1 in the outer region of the MC. Other cascade particles have their major energy delivery in the central and denser core of the MC. From a temperature model (considering CR data from Voyager I), we observed (i) a small bump in temperature at the distance of 3 × 103–2 × 104 au from the center, (ii) a rapid temperature decrease (roughly 7 K) between the outer layer and the second most outer layer, and (iii) that, at a distance of 5 × 104 au (Av > 10), the gas temperature of the MC is below 15 K.

Branching ratios of krypton ions were measured around the 2s edge using synchrotron radiation. The present results are compared with existing theoretical and experimental values. Collective effects of electrons in the 2s orbital might have a significant action. It is shown that one-electron photoionization is enhanced just below this inner-shell threshold. This is due to the fact that the transition of an inner shell electron changes the self-consistent field acting upon the outer electrons, allowing one or several of them to be ejected. This effect is very pronounced in krypton around the 2s edge, where a strong maximum in the seven-fold charged-ion yield occurs near the Kr 2s threshold.

We present a code, called NKABS, to determine optical constants (complex refractive index) of thin films directly from the absorbance data in the infrared. The code is written in the Python language, which is more accurate and faster than previous methods in the literature. For solving the Kramers-Kronig relationship, we used the Maclaurin's methodology. Unlike other codes, which found convergence in 30-40 iterations, the NKABS reach the convergence in just 4 or 5 iterations. Additionally, to evaluate the error, this code calculates the MAPE (Mean Absolute Percentage Error) and the chi-square χ(2). The typical MAPE error obtained using NKABS is less than 1×10(-3)%. To illustrate the functionality of this code, we calculate the optical constants in the infrared spectral region of 28 different samples of astrophysical interest at different temperatures (10-300K), which simulates molecules in space environments, mostly the ones called astrophysical ices. The samples were obtained from the condensation of pure gases (e.g. CO, CO2, NH3, SO2), from the sublimation in vacuum of pure liquids (e.g. water, acetone, acetonitrile, acetic acid, formic acid, ethanol and methanol) and from mixtures of different species (e.g. H2O:CO2, H2O:CO:NH3, H2O:CO2:NH3:CH4). Additionally films of solid biomolecules samples of astrochemistry/astrobiology interest (e.g. glycine, adenine) were probed. The code and the data-base obtained here are available on-line. The NKABS can also be employed to calculate refractive index of processed samples (by heating or radiation). Such data and the refractive index of virgin samples are required as input in several astrophysical models that calculate the radiative transfer in dusty astrophysical environments such as protoplanetary disks and circumstellar environments as well as dense molecular clouds.

In dense and cold regions of the interstellar medium (ISM), molecules may be adsorbed onto dust grains to form the ice mantles. Once formed, they can be processed by ionizing radiation coming from stellar or interstellar medium leading to formation of several new molecules in the ice. Among the different kind of ionizing radiation, cosmic rays play an important role in the solid-phase chemistry because of the large amount of energy deposited in the ices. The physicochemical changes induced by the energetic processing of astrophysical ices are recorded in a intrinsic parameter of the matter called complex refractive index (CRI). In this paper, we present for the first time a catalogue containing 39 complex refractive indices (n, k) in the infrared from 2.0 - 16.6 micrometer for 13 different water-containing ices processed in laboratory by cosmic ray analogs. The calculation was done by using the NKABS (acronym of determination of N and K from ABSorbance data) code, which employs the Lambert-Beer and Kramers-Kronig equations to calculate the values of n and k. The results are also available at the website: http://www1.univap.br/gaa/nkabs-database/data.htm. As test case, a H2O:NH3:CO2:CH4 ice was employed in a radiative transfer simulation of a prototoplanetary disk to show that these data are indispensable to reproduce the spectrum of YSOs containing ices.

The formation of C=C and C≡C bonds from the processing of pure c-C6H12 (cyclo- hexane) and mixed H2O:NH3:c-C6H12 (1:0.3:0.7) ices by highly-charged, and energetic ions (219 MeV 16 O 7+ and 632 MeV 58 Ni 24+ ) is studied. The experiments simulate the physical chemistry induced by medium-mass and heavy-ion cosmic rays in interstellar ices analogs. The measurements were performed inside a high vacuum chamber at the heavy-ion acceler- ator GANIL (Grand Accelerateur National d'Ions Lourds) i n Caen, France. The gas samples were deposited onto a polished CsI substrate previously cooled to 13 K. In-situ analysis was performed by a Fourier transform infrared (FTIR) spectrometry at different ion fluences. Dis- sociation cross section of cyclohexane and its half-life in astrophysical environments were determined. A comparison between spectra of bombarded ices and young stellar sources in- dicates that the initial composition of grains in theses env ironments should contain a mixture of H2O, NH3, CO (or CO2), simple alkanes, and CH3OH. Several species containing double or triple bounds were identified in the radiochemical produc ts, such as hexene, cyclohexene, benzene, OCN − , CO, CO2, as well as several aliphatic and aromatic alkenes and alkynes. The results suggest an alternative scenario for the product ion of unsaturated hydrocarbons and possibly aromatic rings (via dehydrogenation processes) in interstellar ices induced by cosmic ray bombardment.

14 pags., 10 figs., 2 tabs., app., We use experimental mid-infrared optical constants and extended effective medium approximations to determine the porosity and the band strengths of multi-phase composite ices grown at 30 K. A set of porous H2O:CH4 ices are taken as a prototypical example. As a benchmark and proof of concept, the stoichiometry of the ice constituents is retreived with good accuracy from the refractive indices and the extinction coefficients of the reference binary ice mixtures with known compositions. Accurate band strengths are then calculated from experimental mid-infrared spectra of complex ices. We notice that the presence of pores has only a small effect on the overall band strengths, whereas a water dilution can considerably alter them. Different levels of porosity are observed depending on the abundance of methane used as a gas contaminant premixed with water prior to background deposition. The absorption profiles are also found to vary with deposition rate. To explain this, we use Monte Carlo simulations and we observe that the deposition rate strongly affects the pore size distribution as well as the ice morphology through reorganization processes. Extrapolated to genuine interstellar ices, the methodology presented in this paper can be used to evaluate the porosity and to quantify the relative abundances from observational data., Part of this work was supported by NOVA, the , aNetherlands Research School for Astronomy and Vici grant from the Netherlands Organisation for Scientic Research (NWO). J.-B.B. is grateful for support from the Marie Sklodowska Curie actions and the Intra-European Fellowship (FP7- PEOPLE-2011-IEF-299258). S.C. is supported by the Netherlands Organization for Scientific Research (NWO). B.M. and J. O. were supported by the MINECO of Spain under grant FIS2013-48087-C2-1P. S.P. thanks the Brazilian agencies CNPq, CAPES, INCT-A, and FAPESP (JP2009/18304-0; DR2013/07657-5) for financial support.

The methyl formate molecule (HCOOCH3) is one of the most abundant molecules observed in hot molecular cores. Together with acetic acid and the sugar glycolaldehyde, these C2H4O2 molecules are the first triad of isomers detected in interstellar clouds. However, the observations point to a high enhancement in the abundance of methyl formate, which can reach up to 100 times the amount of its second abundant isomer, acetic acid. The observational abundance difference between these isomers has been subject of several works, invoking different formation pathways or survival rates. In this work we present an experimental and theoretical study of photoionization and photodissociation processes of HCOOCH3, to point out clues about its survival to high-energy photons observed in some interstellar environments. In order to obtain the most stable C2H4O2 cations and dications dissociation pathways, spectroscopic and computational methods were used. The measurements were taken employing soft X-ray photons with energies around carbon 1s and oxygen 1s resonances, while the calculations were performed at B3LYP/cc-pVDZ level, at the experimental pressure and temperature. Mass spectra of the photoproduced fragments were obtained using photoelectron photoion coincidence method. The main photodissociation channels are in agreement with the most favourable calculated pathways. Photoionization and photodissociation cross-sections were also determined. The results suggest that the observed high abundance of methyl formate could not be attributed to photodissociation processes.

An experimental photochemistry study involving gas- and solid-phase amino acids (glycine, DL-valine, DL-proline) and nucleobases (adenine and uracil) under soft X-rays was performed. The aim was to test the molecular stabilities of essential biomolecules against ionizing photon fields inside dense molecular clouds and protostellar discs analogs. In these environments, the main energy sources are the cosmic rays and soft X-rays. The measurements were taken at the Brazilian Synchrotron Light Laboratory (LNLS), employing 150-eV photons. In situ sample analysis was performed by time-of-flight mass spectrometer (TOF-MS) and Fourier transform infrared (FTIR) spectrometer, for gas- and solid-phase analysis, respectively. The half-life of solid-phase amino acids, assumed to be present at grain mantles, is at least 3 × 10 5 and 3 × 10 8 yr inside dense molecular clouds and protoplanetary discs, respectively. We estimate that for gas-phase compounds these values increase 1 order of magnitude since the dissociation cross-section of glycine is lower in gas phase than in solid phase for the same photon energy. The half-life of solid-phase nucleobases is about 2–3 orders of magnitude longer than found for amino acids. The results indicate that nucleobases are much more resistant to ionizing radiation than amino acids. We consider these implications for the survival and transfer of biomolecules in space environments.

Water, carbon oxide, carbon dioxide, and ammonia ices are known to be pervasive constituents of the solar system and the interstellar medium. These ices and ice-covered surfaces are exposed to bombardment by energetic projectiles like photons, electrons, and ions. Laboratory experiments have been carried out to study the effects of such irradiation. However, there is a clear lack of information about the interaction of heavy ion components of solar/stellar wind and galactic cosmic rays (e.g. Fe) with ices in the keV to GeV energy range. The objective of this work is to study the effects produced in astrophysical ices by highly charged nickel ions at relatively high energy (∼50–500 MeV) in the electronic energy loss regime, and to compare them with those produced by protons, photons, and electrons. Our results for CO 2 and CO indicate that sputtering induced by heavy ions can be an important mechanism to desorb molecules in astrophysical environments.

Benzene molecules, present in the proto-planetary nebula CRL 618, are ionized and dissociated by UV and X-ray photons originated from the hot central star and by its fast wind. Ionic species and free radicals produced by these processes can lead to the formation of new organic molecules. The aim of this work is to study the photoionization and photodissociation processes of the benzene molecule, using synchrotron radiation and time of flight mass spectrometry. Mass spectra were recorded at different energies corresponding to the vacuum ultraviolet (21.21 eV) and soft X-ray (282-310 eV) spectral regions. The production of ions from the benzene dissociative photoionization is here quantified, indicating that C6H6 is more efficiently fragmented by soft X-ray than UV radiation, where 50% of the ionized benzene molecules survive to UV dissociation while only about 4% resist to X-rays. Partial ion yields of H+ and small hydrocarbons such as C2H2+, C3H3+ and C4H2+ are determined as a function of photon energy. Absolute photoionization and dissociative photoionization cross sections have also been determined. From these values, half-life of benzene molecule due to UV and X-ray photon fluxes in CRL 618 were obtained., The paper contains 8 pages, 9 figures and 4 tables. Accepted to be published on MNRAS on 2008 November 26

We present experimental studies on the photoionization and photodissociation processes (photodestruction) of gaseous amino acids and nucleobases in interstellar and interplanetary radiation conditions analogs. The measurements have been undertaken at the Brazilian Synchrotron Light Laboratory (LNLS), employing vacuum ultraviolet (VUV) and soft X-ray photons. The experimental set up basically consists of a time-of-flight mass spectrometer kept under high vacuum conditions. Mass spectra were obtained using photoelectron photoion coincidence technique. We have shown that the amino acids are effectively more destroyed (up to 70-80%) by the stellar radiation than the nucleobases, mainly in the VUV. Since polycyclic aromatic hydrocarbons have the same survival capability and seem to be ubiquitous in the ISM, it is not unreasonable to predict that nucleobases could survive in the interstellar medium and/or in comets, even as a stable cation., 4 pages, 2 figures. To be published in the Proceedings of the IAU-251 symposium - Organic Mater in Space, Hong Kong, China (2008)

We present experimental results obtained from photoionization and photodissociation processes of abundant interstellar CH$_3$-X type organic molecules like methanol (CH$_3$OH), methylamine (CH$_3$NH$_2$) and acetonitrile (CH$_3$CN) as alternative route for the production of H$_3^+$ in interstellar and star forming environments. The measurements were taken at the Brazilian Synchrotron Light Laboratory (LNLS), employing soft X-ray photons with energies between 200 and 310 eV and time of flight mass spectrometry. Mass spectra were obtained using the photoelectron-photoion coincidence techniques. Absolute averaged cross sections for H$_3^+$ production by soft X-rays were determined. We have found that, among the channels leading to molecular dissociation, the H$_3^+$ yield could reach values up to 0.7% for single photoionization process and up to 4% for process involving double photoionization. The H$_3^+$ photoproduction cross section due to the dissociation of the studied organic molecules by photons over the C1s edge (200-310 eV) were about 0.2-1.4 $\times$ 10$^{-18}$ cm$^2$. Adopting the typical X-ray luminosity $L_X \gtrsim 10^{31}$ erg s$^{-1}$ which best fit the observational data for AFGL 2591 (Stauber et al. 2005) we derive an estimative for the H$_3^+$ photoproduction rate due to methyl-compounds dissociation process. The highest value for the H$_3^+$ column density from methanol dissociation by soft X-rays, assuming a steady state scenario, was about $10^{11}$ cm$^2$, which gives the fraction of the photoproduced H$_3^+$ of about 0.05%, as in the case of dense molecular cloud AFGL 2591. Despite the extreme small value, this represent a new and alternative source of H$_3^+$ into dense molecular clouds and it is not been considered as yet in interstellar chemistry models.

Context. Enceladus, a small icy moon of Saturn, is one of the most remarkable bodies in the solar system. This moon is a geologically active object, and despite the lower temperatures on most of its surface, the geothermally heated south polar region presents geysers that spouts a plume made of water (~90%), carbon dioxide, methane, ammonia, and methanol, among other molecules. Most of the upward-moving particles do not have the velocity to escape from the gravitational influence of the moon and fall back to the surface. The molecules in the ice are continuously exposed to ionizing radiation, such as UV and X-rays photons, cosmic rays, and electrons. Over time, the ionizing radiation promotes molecular bond rupture, destroying and also forming molecules, radicals, and fragments.Aims. We analyse the processing of an ice mixture analogue to the Enceladus fallout ice in cold resurfaced areas (north pole) by 1 keV electrons. The main goal is to search for complex species that have not yet been detected in this moon, and to determine relevant physico-chemical parameters, such as destruction and formation cross-sections and the half-life of the studied molecules in the ice.Methods. The experiment consisted of the electron irradiation of an Enceladus-like ice mixture (H2 O:CO2 :CH4 :NH3 :CH3 OH) in an ultra-high vacuum chamber at 20 K. The analysis was made by infrared spectrometry in the mid-infrared region (4000−800 cm-1 or 2.5−12.5 μ m).Results. The absolute dissociation cross-sections of the parent molecules, the formation cross-section of daughter species, and the half-life of the parental species in a simulated Enceladus irradiation scenario were determined. Among the produced species, CO (carbon monoxide), OCN− (cyanate anion), HCONH2 (formamide), and H2 CO (formaldehyde) were tentatively detected.

In this work, we studied the stability of the glycine molecule in the crystalline zwitterion form, known as {\alpha}-glycine ($^{+}$NH$_{3}$CH$_{2}$COO$^{-}$) under action of heavy cosmic ray analogs. The experiments were conducted in a high vacuum chamber at heavy ions accelerator GANIL, in Caen, France. The samples were bombarded at two temperatures (14 K and 300 K) by $^{58}$Ni$^{11+}$ ions of 46 MeV until the final fluence of $10^{13}$ ions cm$^{-2}$. The chemical evolution of the sample was evaluated in-situ using Fourrier Transformed Infrared (FTIR) spectrometer. The bombardment at 14 K produced several daughter species such as OCN$^-$, CO, CO$_2$, and CN$^-$. The results also suggest the appearing of peptide bonds during irradiation but this must be confirmed by further experiments. The halflives of glycine in Interstellar Medium were estimated to be 7.8 $\times 10^3$ years (300 K) and 2.8 $\times 10^3$ years (14 K). In the Solar System the values were 8.4 $\times 10^2$ years (300 K) and 3.6 $\times 10^3$ years (14 K). It is believed that glycine could be present in space environments that suffered aqueous changes such as the interior of comets, meteorites and planetesimals. This molecule is present in proteins of all alive beings. So, studying its stability in these environments provides further understanding about the role of this specie in the prebiotic chemistry on Earth., Comment: 28 pages, 12 figures, 9 tables. Accepted to be published at Monthly Notices of the Royal Astronomical Society (MNRAS)

Formic acid (HCOOH) has been extensively detected in space environments, including interstellar medium (gas and grains), comets and meteorites. Such environments are often subjected to the action of ionizing agents, which may cause changes in the molecular structure, thus leading to formation of new species. Formic acid is a possible precursor of pre-biotic species, such as Glycine (NH2CH2COOH). This work investigates experimentally the physicochemical effects resulting from interaction of heavy and energetic cosmic ray analogues (46MeV 58Ni11+) in H2O:HCOOH (1:1) ice, at 15 K, in ultrahigh vacuum regime, using Fourier transform infrared spectrometry in the mid-infrared region (4000-600 cm-1 or 2.5-12.5 microns). After the bombardment, the sample was slowly heated to room temperature. The results show the dissociation cross-section for the formic acid of 2.4x10^-13 cm2, and half-life due to galactic cosmic rays of 8x10^7 yr. The IR spectra show intense formation of CO and CO2, and small production of more complex species at high fluences.

We studied the effects produced by the interaction of heavy ion cosmic rays with interstellar and cometary organic molecules in the solid phase. Formic acid (HCOOH) ice at 15 K was irradiated by 267-MeV 56Fe22+ ions and the chemical evolution was analysed using Fourier transform infrared spectroscopy. The destruction cross-section of HCOOH and the formation cross-sections of the produced molecular species have been determined; the sputtering yield values are also discussed. The most abundant chemical species formed by Fe ion irradiation are CO, CO2 and H2O. The half-life of frozen formic acid molecules in the interstellar medium, as a result of interaction with the different cosmic ray constituents, is evaluated to be 108 yr, considering that the destruction cross-section σ d of heavy ions is ruled by a power law as a function of the electronic stopping power Se (i.e. σd ∼ S3/2 e ). Moreover, a complementary study based on mass spectrometry data from the literature has been performed, in order to understand the HCOOH molecule radiolysis, the desorption of its product and the chemical reaction pathways in ice.

Context. Several objects in the Solar System like Europa, Ganymede and Callisto have frozen surface (main component: H2O). The associated thickness is bigger than the penetration depth of the relevant projectile ions. Additionally, other species such as H2O2, SO2 and CO2 have been detected on these surface. The formation mechanisms of these molecules are still under discussion.\ud \ud Aims. We present new experimental results on the implantation of 13Cq+ (q = 2, 3) ions at an energy of 30 keV in water ice at low temperatures (15 and 80 K). Experiments with multiply charged ions at energies of tens of keV are particularly relevant to simulating the complexity of the irradiation environment to which the surfaces of the icy moons in the outer solar system are exposed.\ud \ud Methods. The experiments were performed at the low energy ion beam facility ARIBE of GANIL in Caen (France). 30 keV 13Cq+ (q =\ud 2, 3) ions have been used to bombard solid H,2O surface which were frozen at 15K and 80K. Fourier Transform Infrared Spectrometer (FTIR) was used to analyze the sample in the 5000 - 600 cm-1 (2-16.7 μm) region with a spectral resolution of 1 cm-1.\ud \ud Results. The results of our experiments indicate that implantation produces 13CO2 with yields in the range of 0.32-0.57 molecules ion-1. This yield seems to be independent of the temperature of the ices in the range studied. We have estimated the time scale necessary to accumulate by implantation of magnetospheric carbon ions the observed quantity of carbon dioxide on the surface of Europa, a Jovian moon. This time scale is of the order of 1.0-1.3x104 yrs which is higher than that evaluated for carbon dioxide production by other relevant processes.\ud \ud Conclusions.We conclude that although a relevant quantity of CO2 can be formed by carbon ion implantation, this is not the dominant formation mechanism at Europa.

The presence of soft x-rays is very important for the chemical evolution of interstellar medium and other astrophysical environments close to young and bright stars. Soft X-rays can penetrate deep in molecular clouds and protostellar disks and trigger chemistry in regions in which UV stellar photons do not reach. The effects of soft X-rays in astrophysical ices are also remarkable because they release secondary electrons in and on the surface of the ices, which trigger a new set or chemical reactions. In this chapter we will discuss firstly about the origin and relevance of soft X-rays in astrophysics. Next we will move to the effect of ionizing radiation in organic molecules present in astrophysical environment. We will discuss the use soft X-rays in astrochemistry laboratory studies at both gas- and solid-phase (ice). We will make a review covering our publications in this field, in particular, about the experiments employing time-of-flight spectroscopy (TOF-MS), Fourier transform infrared (FTIR) spectroscopy and photon stimulated ion desorption (PSID-TOF-MS). This study help us to understand the chemical evolution several astrophysical regions and also put constrains in the researches related with the life's origin.

Our groups in Brazil, France and Italy have been active, among others in the world, in performing experiments on physical-chemical effects induced by fast ions colliding with solids (frozen gases, carbonaceous and organic materials, silicates, etc.) of astrophysical interest. The used ions span a very large range of energies, from a few keV to hundreds MeV. Here we present a summary of the results obtained so far on the formation of oxidants (hydrogen peroxide and ozone) after ion irradiation of frozen water, carbon dioxide and their mixtures. Irradiation of pure water ice produces hydrogen peroxide whatever is the used ion and at different temperatures. Irradiation of carbon dioxide and water frozen mixtures result in the production of molecules among which hydrogen peroxide and ozone. The experimental results are discussed in the light of the relevance they have to support the presence of an energy source for biosphere on Europa and other icy moons in the outer Solar System., This research has been supported by the European COST Action CM0805: The Chemical Cosmos.

An experimental study on the interaction of heavy, highly charged, and energetic ions (52 MeV Ni^13+) with pure H2O, pure CO2 and mixed H2O:CO2 astrophysical ice analogs is presented. This analysis aims to simulate the chemical and the physicochemical interactions induced by heavy cosmic rays inside dense and cold astrophysical environments such as molecular clouds or protostellar clouds. The measurements were performed at the heavy ion accelerator GANIL (Grand Accelerateur National d'Ions Lourds in Caen, France). The gas samples were deposited onto a CsI substrate at 13 K. In-situ analysis was performed by a Fourier transform infrared (FTIR) spectrometer at different fluences. Radiolysis yields of the produced species were quantified. The dissociation cross sections of pure H2O and CO2 ices are 1.1 and 1.9E-13 cm^2, respectively. In the case of mixed H2O:CO2 (10:1) the dissociation cross sections of both species are about 1E-13 cm^2. The measured sputtering yield of pure CO2 ice is 2.2E4 molec/ion. After a fluence of 2-3E12 ions/cm^2 the CO2/CO ratio becomes roughly constant (~0.1), independent of the of initial CO2/H2O ratio. A similar behavior is observed for the H2O2/H2O ratio which stabilizes at 0.01, independent of the initial H2O column density or relative abundance., Comment: 13 pages, 9 figures, 4 tables. Accepted to be published in Astronomy and Astrophysics

Icy grain mantles consist of small molecules containing hydrogen, carbon, oxygen and nitrogen atoms (e.g. H2O, CO, CO2, NH3). Such ices, present in different astrophysical environments (giant planets satellites, comets, dense clouds, and protoplanetary disks), are subjected to irradiation of different energetic particles: UV radiation, ion bombardment (solar and stellar wind as well as galactic cosmic rays), and secondary electrons due to cosmic ray ionization of H2. The interaction of these particles with astrophysical ice analogs has been the object of research over the last decades. However, there is a lack of information on the effects induced by the heavy ion component of cosmic rays in the electronic energy loss regime. The aim of the present work is to simulate of the astrophysical environment where ice mantles are exposed to the heavy ion cosmic ray irradiation.Sample ice films at 13K were irradiated by nickel ions with energies in the 1-10 MeV/u range and analyzed by means of FTIR spectrometry. Nickel ions were used because their energy deposition is similar to that deposited by iron ions, which are particularly abundant cosmic rays amongst the heaviest ones.In this work the effects caused by nickel ions on condensed gases are studied (destruction and production of molecules as well as associated cross sections, sputtering yields) and compared with respective values for light ions and UV photons.

This work presents the results for the irradiation of pure SO2 sample that was condensed in a preevacuated chamber, from Laboratorio de Astroquimica e Astrobiologia (LASA/UNIVAP), at low temperature (12 K) and irradiated by ionizing photons which simulate Solar photons in the vacuum ultraviolet (VUV) and soft X-rays range. The infrared spectra of irradiated sample have presented the formation of SO3. Experimental formation cross section was determined. Theoretical investigations were performed at Second-order Moller- Plesset perturbation theory (MP2) level and indicate the most likely SO3 formation channels vary with the reaction supporting medium.

N2-rich ices may exist in various environments in the solar system and interstellar medium. These ices are exposed to ultraviolet photons and cosmic rays, which may cause changes in the molecular structure, thus leading to formation of new species. In this study we investigated experimentally the production of N3 from the irradiation of N2- rich ices, using soft X-rays and cosmic rays analog. The results of the experiments using these sources of radiation showed that the azide radical, N3, was observed in ices that have been bombarded by ions and in those that have been photolyzed (range of vacuum ultraviolet and soft X-rays).

In order to simulate the effects of energetic charged particles present in the solar wind colliding with the cometary gaseous formic acid molecule (HCOOH), laboratory experiments have been performed. The absolute ionisation and dissociation cross sections for this molecule interacting with solar wind particles were measured employing fast electrons in the energy range of 0.5 to 2 keV and energetic protons with energies varying from 0.128 to 2 MeV. Despite the fact that both projectiles lead to a very similar fragmentation pattern, differences in the relative intensities of the fragments were observed. Formic acid survives about 4-5 times more to the proton beam than to the energetic electron collision.The minimum momentum transfer in the electron impact case was estimated to be 3-38% larger than the minimum momentum transfer observed with the equivelocity protons. The UV photodissociation rates and half-lives for HCOOH are roughly closer to the values obtained with energetic electrons. It is consequently important to take electron impact data into account when developing chemical models to simulate the interplanetary conditions., Comment: 11 pages, 7 figures, 5 tables, Accepted to be published in MNRAS

Fragments from organic molecule dissociation (such as reactive ions and radicals) can form interstellar complex molecules like amino acids. The goal of this work is to experimentally study photoionization and photodissociation processes of acetic acid (CH$_3$COOH), a glycine (NH$_2$CH$_2$COOH) precursor molecule, by soft X-ray photons. The measurements were taken at the Brazilian Synchrotron Light Laboratory (LNLS), employing soft X-ray photons from a toroidal grating monochromator (TGM) beamline (100 - 310 eV). Mass spectra were obtained using the photoelectron photoion coincidence (PEPICO) method. Kinetic energy distribution and abundances for each ionic fragment have been obtained from the analysis of the corresponding peak shapes in the mass spectra. Absolute photoionization and photodissociation cross sections were also determined. We have found, among the channels leading to ionization, that only 4-6% of CH$_3$COOH survive the strong ionization field. CH$_3$CO$^+$, COOH$^+$ and CH$_3^+$ ions are the main fragments, and the presence of the former may indicate that the production-destruction process of acetic acid in hot molecular cores (HMCs) could decrease the H$_2$O abundance since the net result of this process converts H$_2$O into OH + H$^+$. The COOH$^+$ ion plays an important role in ion-molecule reactions to form large biomolecules like glycine., Comments: 8 pages, 5 figures, 3 tables. Accepted to be printed in A&A

Formic acid is much more abundant in the solid state, both in interstellar ices and cometary ices, than in the interstellar gas (ice/gas ~ 10^{4}) and this point remains a puzzle. The goal of this work is to experimentally study ionization and photodissociation processes of HCOOH (formic acid), a glycine precursor molecule. The measurements were taken at the Brazilian Synchrotron Light Laboratory (LNLS), employing soft X-ray photons from toroidal grating monochromator TGM) beamline (200 - 310 eV). Mass spectra were obtained using photoelectron photoion coincidence (PEPICO) method. Kinetic energy distributions and abundances for each ionic fragment have been obtained from the analysis of the corresponding peak shapes in the mass spectra. Photoionization and photodissociation cross sections were also determined. Due to the large photodissociation cross section of HCOOH it is possible that in PDRs regions, just after molecules evaporation from the grain surface, formic acid molecules are almost totally destroyed by soft X-rays, justifying the observed low abundance of HCOOH in the gaseous phase. The preferential path for the glycine formation from formic acid may be through the ice phase reaction. Keywords: HCOOH; Photoionization; X-rays; Astrochemistry., Comment: 9 pages, 7 figures, 2 tables. Accepted to be printed in A&A

We present experimental studies on the interaction of soft X-rays on gas-phase and solid-phase amino acids and nucleobases in an attempt to verify if these molecules (supposed to be formed in molecular clouds/protostellar clouds) can survive long enough to be observed or even to be found in meteorites. Measurements have been undertaken employing 150 eV photons under high vacuum conditions at the Brazilian Synchrotron Light Laboratory (LNLS). The produced ions from the gas-phase experiments (glycine, adenine and uracil) have been mass/charge analyzed by time-of-flight spectrometer. The analysis of solid phase samples (glycine, DL-proline, DL-valine, adenine and uracil) were performed by a Fourier transform infrared spectrometer coupled to the experimental chamber. Photodissociation cross sections and halflives were determined and extrapolated to astrophysical environments. The nucleobases photostability was up to two orders of magnitude higher than for the amino acids.

In this work, we investigate the possible effects produced by soft X-rays (and secondary electrons) on Titan aerosol analogs in an attempt to simulate some prebiotic photochemistry. The experiments have been performed inside a high vacuum chamber coupled to the soft X-ray spectroscopy beamline at the Brazilian Synchrotron Light Source (LNLS). In-situ sample analysis were performed by a Fourier transform infrared spectrometer. The infrared spectra have presented several organic molecules, including nitriles and aromatic CN compounds. After the irradiation, the brownish-orange organic residue was analyzed ex-situ by gas chromatographic technique revealing the presence of adenine (C5H5N5), one of the constituents of the DNA molecule.

Ionization and dissociation of the formic acid molecule (HCOOH) by energetic charged particles have been studied for 1 keV electrons and nearly equivelocity 2 MeV protons. Whereas the fragmentation pattern induced by impact of electron and proton show close similarities, some distinctions in the fragmentation yields were observed for these equivelocity projectiles.