Valine Radiolysis by H+, He+, N+, and S15+ MeV Ions

International audienceRadiolysis of biomolecules by fast ions has interest in medical applications and astrobiology. The radiolysis of solid D-valine (0.2-2 µm thick) was performed at room temperature by 1.5 MeV H + , He + , N + , and 230 MeV S 15+ ion beams. The samples were prepared by spraying/dropping valine-water-ethanol solution on ZnSe substrate. Radiolysis was monitored by infrared spectroscopy (FTIR) through the evolution of the intensity of the valine infrared 2900, 1329, 1271, 948, and 716 cm −1 bands as a function of projectile fluence. At the end of sample irradiation, residues (tholins) presenting a brownish color are observed. The dependence of the apparent (sputtering + radiolysis) destruction cross section, σ d , on the beam stopping power in valine is found to follow the power law σ d = aS e n , with n close to 1. Thus, σ d is approximately proportional to the absorbed dose. Destruction rates due to the main galactic cosmic ray species are calculated, yielding a million year half-life for solid valine in space. Data obtained in this work aim a better understanding on the radioresistance of complex organic molecules and formation of radioproducts

Modification of ices by cosmic rays and solar wind

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Strong perturbation effects in heavy ion induced electronic sputtering of lithium fluoride

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A simple model for Ice compaction data induced by low energy Ion irradiation

Una conexión entre la compactación del agua sólida amorfa (ASW) durante la irradiación de iones energéticos y la desaparición de los enlaces colgantes de agua (OH-db) ha sido analizada particularmente por Palumbo et al. y por Baragiola et al. En este trabajo, se presenta una discusión adicional del proceso para inducir la compactación. Se discuten modelos simples para la evolución de OH-db para hielo de agua irradiado. Resultados de la literatura sobre la desaparición de OH-db en hielos bombardeados por iones H + de 100–200 keV y sobre la comparación de los resultados de porosidad y OH-db para 200 keV Ar +Se revisan los iones. Se observa que tanto para la disminución de la porosidad (compactación) como para la disminución de la señal de absorción de OH-db, los datos experimentales pueden ajustarse bien mediante la suma de dos exponenciales decrecientes con conjuntos de parámetros similares. Aunque no se puede extraer una explicación clara de esta correlación, sugiere firmemente que la compactación y la destrucción de OH-db son desencadenadas por dos procesos diferentes.A connection between the compaction of amorphous solid water (ASW) during energetic ion irradiation and the disappearing of water dangling bonds (OH-db) has been analyzed particularly by the Palumbo et al. and by Baragiola et al. In this work, a further discussion of the process for inducing the compaction is presented. Simple models for OH-db evolution for irradiated water ice are discussed. Literature results on the OH-db disappearance in ices bombarded by 100–200 keV H+ ions and on the comparison of porosity and OH-db results for 200 keV Ar+ ions are revisited. It is observed that for both, porosity decrease (compaction) and OH-db absorption signal decrease, experimental data can be well fitted by the sum of two decreasing exponentials with similar sets of parameters. Although a clear explanation for this correlation cannot be extracted, it suggests strongly that compaction and OH-db destruction are both triggered by two different processes

Alkali Halide Nanotubes: Structure and Stability

Accurate density functional theory (DFT) and coupled-cluster (CCSD) calculations on a series of (LiF)_{<i>n</i>=2,36} neutral clusters suggest that nanotube structures with hexagonal and octagonal transversal cross sections show stability equal to or greater than that of the typical cubic form of large LiF crystals. The nanotube stability was further corroborated by quantum dynamic calculations at room temperature. The fact that stable nanotube structures were also found for other alkali halides (e.g., NaCl and KBr) suggests that this geometry may be widely implemented in material sciences