An infrared study of solid glycine in environments of astrophysical relevance

9 p.: gráf.The conversion from neutral to zwitterionic glycine is studied using infrared spectroscopy from the point of view of the interactions of this molecule with polar (water) and non-polar (CO2, CH4)surroundings. Such environments could be found on astronomical or astrophysical matter.The samples are prepared by vapour-deposition on a cold substrate (25 K), and then heated up to sublimation temperatures of the co-deposited species. At 25 K, the neutral species is favoured over the zwitterionic form in non-polar environments, whereas for pure glycine, or in glycine/water mixtures, the dominant species is the latter. The conversion is easily followed by the weakening of two infrared bands in the mid-IR region, associated to the neutral structure. Theoretical calculations are performed on crystalline glycine and on molecular glycine, both isolated and surrounded by water. Spectra predicted from these calculations are in reasonable agreement with the experimental spectra, and provide a basis to the assignments. Different spectral features are suggested as probes for the presence of glycine in astrophysical media, depending on its form (neutral or zwitterionic), their temperature and composition. © the Owner Societies 2011Funding from the Spanish Ministry of Education, Projects FIS2007-61686 and FIS2010-16455.Financial support from Ministerio de Ciencia e Innovación, ‘‘Ramón y Cajal’’ program and CSIC, JAE-Doc ProgramPeer reviewe

Solid L-α-alanine: Spectroscopic properties and theoretical calculations

A spectroscopic study of L-α-alanine in different environments is presented, with special emphasis on the neutral to zwitterion transformation of this amino acid. Spectra of room temperature solids as deposited from the vapour and in KBr pellets are compared and discussed revealing some discrepancies. An assignment is proposed based on theoretical calculations of the solid structure. Vapour deposits at 25K are prepared both of pure alanine and of mixtures with polar (H 2O) and non-polar (CO 2, CH 4) components. The spectra of the solids contain IR bands which can be individually assigned to the neutral and to the zwitterion, and whose relative intensity variation can be used to follow the neutral to zwitterion transformation. The assignment of the spectrum of the neutral species is proposed, again with help from theoretical calculations of the single neutral molecule. The neutral/zwitterion ratio in deposits at 25K varies between ~60% for pure alanine and H 2O mixtures and ~90% for non-polar matrices. This ratio drops when the solid is heated until the ionic species only remains at 200K. The conversion process depends on the environment surrounding the alanine molecules. © 2012 Elsevier Ltd.funding from the Spanish Ministry of Science and Innovation, ProjectFIS2010-16455. financial support from Ministerio de Ciencia e Innovación, “Ramón y Cajal” programme and CSIC, JAE-Doc Programme, Sabbatical ProjectPR2010-0012.Peer Reviewe

Polycrystalline thin films of antimony selenide via chemical bath deposition and post deposition treatments

We report a method for obtaining thin films of polycrystalline antimony selenide via chemical bath deposition followed by heating the thin films at 573 K in selenium vapor. The thin films deposited from chemical baths containing one or more soluble complexes of antimony, and selenosulfate initially did not show X-ray diffraction (XRD) patterns corresponding to crystalline antimony selenide. Composition of the films, studied by energy dispersive X-ray analyses indicated selenium deficiency. Heating these films in presence of selenium vapor at 573 K under nitrogen (2000 mTorr) resulted in an enrichment of Se in the films. XRD peaks of such films matched Sb2Se3. Evaluation of band gap from optical spectra of such films shows absorption due to indirect transition occurring in the range of 1 – 1.2 eV. The films are photosensitive, with dark conductivity of about 2x10-8 (V cm)-1 and photoconductivity, about 106 (V cm)1 under tungsten halogen lamp illumination with intensity of 700 W m2. An estimate for the mobility life time product for the film is 4x10-9 cm2 V-1

Thin films of AgIn5(S/Se)8 prepared in a two stage process.

AgIn5(S/Se)8 thin films were prepared by sequential chemical deposition of In2S3–Ag2Se stack films and post-deposition thermal annealing in N2 atmosphere. The formations of AgIn5S8-xSex alloy was achievable through the post-deposition treatment at 350 and 400 C. X-ray diffraction and energy dispersive X-ray analyses were performed on the samples. The direct optical band gap value Eg for the films was found to be as the order of 1.75 eV at room temperature. The photo-response measurements exhibited that AgIn5(S/Se)8 thin films are photoconductive and p-type electrical conductivity of 6.6 9 10-6 (X cm)-1 and thermoelectric power of +18 lV/K

Thermo- and cathodoluminescence properties of lepidolite

Lepidolite, K(Li,Al)3(Si,Al)4O10(F,OH)2, and many of the related phyllosilicate mineral of the mica group have been well studied from the chemical and structural point of view; however, to the best of our knowledge, studies on their luminescence properties have been scarcely reported. This work focuses on the thermoluminescence (TL) and cathodoluminescence (CL) response of a natural lepidolite from Portugal previously characterized by means of environmental scanning electron microscope (ESEM) and X-ray fluorescence (XRF) and atomic absorption spectroscopy (AAS) techniques. The complexity of the thermoluminescence glow curves of non-irradiated and 1Gy irradiated samples suggests a structure of a continuous trap distribution involving multiorder kinetics. UV-IR CL spectral emission shows seven peaks centered at 330, 397, 441, 489, 563, 700 and 769 nm. Such emission bands could be due to (i) structural defects, i. e. [AlO4] or non-bridging oxygen hole centers, and (ii) the presence of point defects associated with Mn2+ and Fe3+.Peer Reviewe

Thermoluminescence response of gamma-irradiated sesame with mineral dust

The thermoluminescence (TL) emission of minerals isolated from Mexican and Indian sesame seeds appear as a good tool to discern between irradiated and non-irradiated samples. According to the X-ray diffraction and environmental scanning microscope, the adhered dust in both samples is mainly composed by different amounts of quartz and feldspars. These mineral phases exhibit (i) enough sensitivity to ionizing radiation inducing good TL intensity, (ii) high stability of the TL signal during the storage of the material (i.e. low fading) and (iii) are thermally and chemically stable. Blind tests performed under laboratory conditions, but simulating industrial preservation processes (similar temperature and moisture, and presence of white light), allows us to distinguish between 1 kGy gamma-irradiated and non-irradiated samples even 11000 hours (15 months) after the irradiation proceeding.This work has been partially supported by the Ministerio de Sanidad y Consumo-CIEMAT (08/156) contract. We also are grateful to project CGL2009- 09247 of the Spanish PLAN NACIONAL DE I+D+i for financial support to perform sample analyses. Y.R.L also acknowledges financial support from JAE-Doc Program (CSIC)Peer Reviewe

Optical constants of NH3 and NH3:N2 amorphous ices in the near-infrared and mid-infrared regions

Ammonia ice has been detected on different astrophysical media ranging from interstellar medium (ISM) particles to the surface of various icy bodies of our solar system, where nitrogen is also present. We have carried out a detailed study of amorphous NH3 ice and NH3:N2 ice mixtures, based on infrared (IR) spectra in the mid-IR (MIR) and near-IR (NIR) regions, supported by theoretical quantum chemical calculations. Spectra of varying ice thicknesses were obtained and optical constants were calculated for amorphous NH3 at 15 K and 30 K and for a NH3:N2 mixture at 15 K over a 500-7000 cm-1 spectral range. These spectra have improved accuracy over previous data, where available. Moreover, we also obtained absolute values for the band strengths of the more prominent IR features in both spectral regions. Our results indicate that the estimated NH3 concentration in ISM ices should be scaled upward by 30%. © 2013. The American Astronomical Society. All rights reserved.Peer Reviewe

Cyanate ion in compact amorphous water ice

7 p.: gráf.The 4.62 μm infrared (2164.5 cm–1) absorption band, observed in ice mantels toward many young stellar objects, has been mostly attributed to the ν3 (CN stretch) band of OCN– ions. We present in this work a spectroscopic study of OCN– ions embedded in compact amorphous ice in a range of concentrations and temperatures relevant to astronomical observations together with quantum mechanical calculations of the ν3 band of OCN– in various H2O environments. The ice samples containing the ions are prepared through hyperquenching of liquid droplets of K+OCN– solutions on a substrate at 14 K. The ν3 OCN– band appears as a broad feature peaking at 4.64 μm with a secondary maximum at 4.54 μm and is much weaker than the corresponding peak in the liquid solution or in the solid salt. A similar weakening is observed for other OCN– absorption peaks at 7.66 μm (2ν2) and 8.20 μm (ν1). The theoretical calculations for the ν3 vibration lead to a range of frequencies spanning the experimentally observed width. This frequency spread could help explain the pronounced drop in the band intensity in the ice. The OCN– ν3 band in the present compact ices is also broader and much weaker than that reported in the literature for OCN– ions obtained by variously processing porous ice samples containing suitable neutral precursors. The results of this study indicate that the astronomical detection of OCN– in ice mantels could be significantly impaired if the ion is embedded in a compact water network.© 2012. The American Astronomical SocietyFunding from the Spanish Ministry of Education, Project FIS2010-16455, and within the frame of the Unidad Asociada UCM-CSIC. financial support from CSIC, JAE-Doc Program. Part of the computations has been carried out at CESGA, FinisTerrae (Spain). Financial support from the Spanish Ministry of Science and Innovation, Project CTQ-2008-02578/BQU.Peer reviewe

Gamma radiation-induced thermoluminescence emission of minerals adhered to Mexican sesame seeds

The thermoluminescence (TL) emission of minerals isolated from Mexican sesame seeds appear as a good tool to discern between irradiated and non-irradiated samples. According to the X-ray diffraction (XRD) and environmental scanning electron microscope (ESEM) data, the adhered dust in both samples is mainly composed of different amounts of quartz and feldspars. These mineral phases exhibit (i) enough sensitivity to ionizing radiation inducing good TL intensity, (ii) high stability of the TL signal during the storage of the material, i.e. low fading, and (iii) are thermally and chemically stable. Blind tests were performed under laboratory conditions, but simulating industrial preservation processes, allow us to distinguish between 1. kGy gamma-irradiated and non-irradiated samples even 15 months after irradiation processing followed the EN 1788 European Standard protocol in sesame samples. © 2012 Elsevier Ltd.This work has been partially supported by the Ministerio de Sanidad y Consumo-CIEMAT (08/156) contract. The first author (Y. Rodríguez-Lazcano) also acknowledges financial support from JAE-Doc Program (CSIC).Peer Reviewe

The formation of carbamate ions in interstellar ice analogues

Carbon dioxide and ammonia are two of the most abundant species in astrophysical media, where they can react in the solid phase under certain conditions. This contribution presents a study of this reaction both in the presence of water and for anhydrous samples. It is shown that after deposition at 15 K, the reaction can start by warming the deposit, and the process continues on up to a temperature of 220 K. Reaction products are studied using infrared spectroscopy and mass spectrometry. For anhydrous samples, a 2:1 stoichiometry mixture of NH3:CO2 gives the highest yield of products. The reaction is favored when a small amount of water is present, which enables ammonia and carbon dioxide molecules to collide within the pores and channels of the amorphous water solid. Large concentration of water, on the other hand, hampers such collisions. The main reaction product is found to be ammonium carbamate, but also carbamic acid is formed, and, in the presence of water, ammonium bicarbonate is produced as well. Theoretical calculations are carried out to provide the basis for the assignment of the spectra. Some of the experiments presented in this contribution consist of the generation of a compact water ice matrix where the carbamate and ammonium ions are embedded. If such a system was found in astrophysical media, it is shown that the ammonium ion could not be detected, whereas two infrared features of the carbamate ion in the 1040 to 1115 cm-1 (9 to 9.6 μm) region could enable the observation of this species. © 2014 the Owner Societies.Funding from the Spanish Ministry of Education, Projects FIS2010-16455. O. G. and Y. R.-L. acknowledge financial support from Ramón y Cajal Program and CSIC, JAE-Doc Program, respectively.Peer Reviewe