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[EN] Vapor pressure is a relevant quantity that is necessary in order to improve the study of the atmosphere dynamics that take place within astrophysical scenarios. The aim of this study was to obtain the vapor pressure values of the following molecules: C2H4, C2H6, CH3OH, CH4, CO, CO2, H2O, and N-2 through experimentation, as well as to determine their empirical relationship with the temperature, applying the results to the persistence of volatiles in trans-Neptunian objects (TNOs) and Kuiper Belt objects (KBOs). The experimental determination was performed by measuring the sublimation rate for each molecule at different temperatures. The Hertz-Knudsen equation was used to obtain the vapor pressures for the aforementioned molecules, taking the necessary considerations into account, and the sublimation rate was measured using a quartz crystal microbalance. In order to check the validity of the methods used, the results obtained for water ice were compared with those of previous studies from the literature. The values obtained for CO, N-2, and CH4 are of particular interest in the study of the TNOs' and KBOs' atmosphere composition. The results of this study improve the understanding of the surface and atmospheric composition of objects in the cold scenarios of the solar system, in particular, in KBOs and TNOs.

[EN] This work calculates the Lorentz-Lorenz coefficient with the refractive index and density values of various molecules in their solid phase measured in our laboratory under astrophysical conditions. This was completed for a range of temperatures from 13 K to close to the sublimation temperature for each molecule. The studied molecules were N-2, CO2, NH3, CH4, CH3OH, C2H4, and C2H6. For CO2, our results match those found in the unique similar previous work in the literature. The results obtained for NH3 and CH3OH are relevant because they confirm that the procedure adopted is applicable also to polar molecules. The study presented here updates the previous work on these molecules by focusing on their solid states under astrophysical conditions and at a range of temperatures. The knowledge of the Lorentz-Lorenz coefficient in a specific temperature range allows for calculating the density using only the refractive index

[EN] Aims. The effective medium approximations (EMAs), or the Lorentz-Lorenz, Maxwell-Garnett, and Bruggeman models, largely used to obtain optical properties and porosities of pure and ice mixtures, have been experimentally tested in this work. The efficiency of these approximations has been studied by obtaining the porosity value for carbon dioxide ice grown at low temperatures. An explanation of the behaviour of the experimental results for all temperatures is given. The analysis carried out for CO2 can be applied to other molecules. Methods. An optical laser interference technique was carried out using two laser beams falling on a growing film of ice at different incident angles which allowed us to determine the refractive index and the thickness of the film. The mass deposited is recorded by means of a quartz crystal microbalance. Porosity is determined from its equational definition by using the experimental density previously obtained. Results. From the experimental results of the refractive index and density, porosity values for carbon dioxide ice films grown on a cold surface at different temperatures of deposition have been calculated and compared with the results obtained from the EMA equations, and with recent experimental results. Conclusion. The values of porosity obtained with the EMA models and experimentally, show similar trends. However, theoretical values overestimate the experimental results. We can conclude that using the EMAs to obtain this parameter from an ice mixture must be carefully considered and, if possible, an alternative experimental procedure that allows comparisons to be made should be used.

[EN] Contact. The increasing capabilities of space missions like the James Webb Space Telescope or ground-based observatories like the European Extremely Large Telescope demand high quality laboratory data of species in astrophysical conditions for the interpretation of their findings. Aims. We provide new physical and spectroscopic data of solid methanol that will help to identify this species in astronomical environments. Methods. Ices were grown by vapour deposition in high vacuum chambers. Densities were measured via a cryogenic quartz crystal microbalance and laser interferometry. Absorbance infrared spectra of methanol ices of different thickness were recorded to obtain optical constants using an iterative minimization procedure. Infrared band strengths were determined from infrared spectra and ice densities. Results. Solid methanol densities measured at eight temperatures vary between 0.64 g cm(-3) at 20 K and 0.84 g cm(-3 )at 130 K. The visible refractive index at 633 nm grows from 1.26 to 1.35 in that temperature range. New infrared optical constants and band strengths are given from 650 to 5000 cm(-1) (15.4-2.0 mu m) at the same eight temperatures. The study was made on ices directly grown at the indicated temperatures, and amorphous and crystalline phases have been recognized. Our optical constants differ from those previously reported in the literature for an ice grown at 10 K and subsequently warmed. The disagreement is due to different ice morphologies. The new infrared band strengths agree with previous literature data when the correct densities are considered.

[EN] The desorption process of methanol in the hot cores of massive young stars is addressed in this work. The study of pure methanol ice and when it is mixed or layered with water allows a better understanding of the physical and chemical processes which could have occurred during the formation of methanol and it is possible to infer the range of temperatures within which methanol can be found in the gas phase in these scenarios. The goal of this study was to model the desorption process of methanol as pure ice and mixed or layered with water under the conditions present in the early stages of hot cores whichcharacterize young star formation. The simulations of desorption of methanol, when it stands alone, performed in this work were compared to the values obtained by other authors to validate the method presented. In this work, the desorption of a water: methanol mixture under astrophysical conditions is also simulated. The theoretical results obtained for layered mixtures match with the temperatures at which an increase of the presence of methanol in the gas phase is detected when young massive mass stars are observed. This study has been performed using the frequency variation of a quartz crystal microbalance which provides a direct measure of the desorbing molecules during the experiments. This process was modelled using the Polanyi-Wigner equation and applied to astrophysical scenarios.

[EN] In this work the frequency factor and the influence of the temperature on this parameter, for zeroth order desorption processes, has been experimentally determined for eight molecules of astrophysical interest. In the literature, this parameter has been estimated indirectly, obtaining values that differ by as much as three orders of magnitude from different authors. As a consequence, there are very different desorption rates reported for the same molecule and additionally its temperature dependence has been systematically neglected. The frequency factor is widely used to model the dynamics of these species under low temperature conditions present in some astrophysical environments. The method reported in this work is based on the analysis of the signal of a quartz crystal microbalance acting as a sample-holder, which is able to directly detect molecules desorbing from it. Two different types of desorption experiments were necessary for this study. In a first set of experiments, carried out at a constant rate of warming up, the desorption energy is obtained. The second set of experiments were performed at several constant temperatures to calculate the frequency factor and its relationship with temperature. The reasons for some anomalous behaviour have been analyzed. The dependence of the frequency factor on temperature should be taken into account when the Polanyi-Wigner equation is used for desorption processes. Every molecule has to be independently studied as no global tendency is found for the variation of the frequency factor with temperature. (C) 2018 Elsevier Ltd. All rights reserved.

[EN] Desorption energy is a relevant parameter when studying the desorption kinetics of an ice under astrophysical conditions. Values reported are generally calculated using at least a desorption experiment and a further data analysis at present. In this work the establishment of a simple rule that relates the desorption energy of a species to the temperature of its desorption peak is explored. The paper presents the results obtained from zeroth-order desorption experiments, based on the use of a quartz crystal microbalance to monitor the loss of weight during desorption of the accreted ice sample under high-vacuum conditions, of nine different molecules covering a wide range of desorption energies. During these experiments, the ice desorption rate reaches a maximum at a certain temperature depending on the molecule. The formula obtained in this study facilitates the estimation of the desorption energy and is valid for all the investigated molecules. Based on these experimental results and simulations, the theoretical expression obtained is valid to calculate desorption energy for zeroth- and first-order desorption experiments under high- or ultrahigh-vacuum conditions using different ice thickness films.

[EN] We report the density and refractive index, at 633 nm, of ethane and ethylene ices at temperatures from 13 to 65 K, measured by double laser interferometry and a cryogenic quartz crystal microbalance in a high vacuum chamber. Both quantities rise with the temperature of deposition from 13 K up to a plateau, 40 K for ethane and 22 K for ethylene. An amorphous structure is suggested for temperatures below 40 K for ethane and below 20 K for ethylene. Above these temperatures, 40 K for ethane and 20 K for ethylene, a crystalline structure is proposed. Ethylene results deviate from linear growth between 25 and 35 K, where a metastable structure is reported in the literature. Density values increase from about 0.40 to 0.60 g cm(-3) for ethane and from about 0.45 to almost 0.65 g cm(-3) for ethylene. The real part of the refractive index changes from about 1.27 to 1.45 for ethane and from about 1.30 to almost 1.48 for ethylene. Results are relevant especially to the outer Solar System, where the presence of these molecules is reported, and for experiments involving them. (C) 2017 Elsevier Inc. All rights reserved.

[EN] We present a spectroscopic study of methane-ethane ice mixtures. We have grown CH4:C2H6 mixtures with ratios 3:1, 1:1, and 1:3 at 18 and 30 K, plus pure methane and ethane ices, and have studied them in the near-infrared (NIR) and mid-infrared (MIR) ranges. We have determined densities of all species mentioned above. For amorphous ethane grown at 18 and 30 K we have obtained a density of 0.41 and 0.54 g cm(-3), respectively, lower than a previous measurement of the density of the crystalline species, 0.719 g cm(-3). As far as we know this is the first determination of the density of amorphous ethane ice. We have measured band shifts of the main NIR methane and ethane features in the mixtures with respect to the corresponding values in the pure ices. We have estimated band strengths of these bands in the NIR and MIR ranges. In general, intensity decay in methane modes was detected in the mixtures, whereas for ethane no clear tendency was observed. Optical constants of the mixtures at 30 and 18 K have also been evaluated. These values can be used to trace the presence of these species in the surface of trans-Neptunian objects. Furthermore, we have carried out a theoretical calculation of these ice mixtures. Simulation cells for the amorphous solids have been constructed using a Metropolis Monte Carlo procedure. Relaxation of the cells and prediction of infrared spectra have been carried out at density functional theory level.

[EN] We have experimentally determined the polarizability of using the Lorentz-Lorenz equation by simultaneously measuring the density and the refractive index. The conditions were solid phase, mbar pressure, and temperature range 10-86 K. The polarizability value compares well with previous gas-phase experimental results and the results from simulations, and does not depend on the temperature of ice formation. This value is constant in the temperature range studied, despite a structural change from amorphous to crystalline.

NOTICE: this is the author’s version of a work that was accepted for publication in Vacuum. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in VACUUM [122 (2015) 154-160] DOI 10.1016/j.vacuum.2015.09.021, The C2H6 molecule has been used to determine experimentally, for the first time, the frequency factor present in the Polanyi-Wigner equation and to study how temperature influences this magnitude for a zeroth order desorption. This parameter is necessary to calculate the desorption rates for environments in which this process occurs. The method presented is based on the analysis of a quartz crystal microbalance signal. In the literature the frequency factor is not experimentally obtained but is rather assumed to be K-6.T/h (at 50 K), as proposed by the activated state theory for first order desorption processes, or it is estimated by other methods. Additionally, the factor's variation with temperature has not been experimentally explored to date. Two different types of zeroth order desorption experiments have been designed for this study. The purpose of the first experiment, carried out at a constant rate of warming, is to obtain the desorption energy, which is compared with previous values reported in the literature. The second group of desorption experiments is performed at constant temperatures and is used to calculate and study the frequency factor. Several temperatures have been specifically selected, enabling us to determine the influence of the temperature on this parameter. We have calculated a relationship for the frequency factor and temperature, obtaining an increase of approximately 50% for the frequency factor for an increase of only 6 K. This result must be taken into account when the Polanyi-Wigner equation is used for desorption rate calculations. (C) 2015 Elsevier Ltd. All rights reserved.

En el presente trabajo se presenta un nuevo método de obtención de índices de refracción y espesores de películas delgadas, desarrollado por el grupo de astrofísica del Centro de Tecnologías Físicas: Acústica, Materiales y Astrofísica, cuyo laboratorio se encuentra en la Escuela Politécnica Superior de Alcoy. La novedad del método radica en el hecho de que el índice puede ser obtenido únicamente con la medida de la reflectancia mientras la película es crecida sobre un substrato, en nuestro caso de oro.

[ES] En este trabajo se presentan los resultados de experimentos de laboratorio enfocados a obtener la densidad y el índice de refracción (parte real) de mezclas de compuestos binarios en estado sólido. La densidad de las mezclas CO2:CH4 obedece a los resultados esperables a partir de los valores individuales de densidad y las proporciones en las mezclas, mientras que las otras dos mezclas binarias estudiadas, CO2:N2 y CH4:N2 presentan densidades hasta un 20 % inferiores a lo esperado. El valor del índice de refracción obtenido para las tres mezclas binarias se desvía hasta un 5 % del valor teórico esperable, siendo superiores en el caso de la mezcla CO2:CH4 e inferiores para CO2:N2 y CH4: N2.

[ES] La principal conclusión de este trabajo es que el color final que emiten los LEDs depende de la temperatura final de trabajo. Si ésta varía lleva asociada un cambio en la cromaticidad, que en algunos casos llega a ser detectable a simple vista. Además los LEDs de diferentes colores (azul, verde, rojo) no cambian del mismo modo para iguales variaciones de temperatura, haciendo de éste un trabajo necesario para el control de la luz finalmente emitida por los diodos.

[ES] El objetivo del presente trabajo es mostrar el equipamiento experimental que dispone nuestro grupo de investigación sobre hielos de interés astrofísico en Alcoy. Dicho equipo experimental está diseñado para intentar reproducir las condiciones en las que se encuentran los hielos en diferentes entornos astrofísicos: bajas temperaturas (del orden de las decenas de K) y bajas presiones (alrededor de 10-7 mbar, denominado como alto vacío). Sin embargo la versatilidad de nuestro equipo experimental permite adaptarlo a diferentes condiciones de trabajo para realizar otro tipo de estudios.