The use of Planetary Nebulae precursors in the study of Diffuse Interstellar Bands

We present the first results of a systematic search for Diffuse Interstellar Bands in a carefully selected sample of post-AGB stars observed with high resolution optical spectroscopy. These stars are shown to be ideal targets to study this old, intriguing astrophysical problem. Our results suggest that the carrier(s) of these bands may not be present in the circumstellar environments of these evolved stars. The implications of the results obtained on the identification of the still unknown carrier(s) are discussed.Comment: 4 pages, 2 figures, proceedings of the conference 'Planetary Nebulae as Astrophysical Tools', held in Gdansk, Poland (June 28 - July 2, 2005

On the spectral features of dangling bonds in CH4/H2O amorphous ice mixtures

[EN] Dangling bond (DB) bands in IR spectra, above 3600 cm(-1), are a source of information on structural properties of amorphous water ice, and especially on ice mixtures of water and other frozen gases. We deal in this paper with the spectroscopic behavior of DB bands of CH4/H2O mixtures. We use ab initio methodology to predict theoretical results which are compared with experimental results. Our model mixtures are created by inserting a variable number of molecules of either species into a cell of appropriate size to reach an initial density of 1 g cm(-3), which can be modified by including an empty space at the top, to simulate pores. The cell is taken as a unit cell for a solid state calculation The structure of the mixture is optimized and the IR spectrum is calculated for the converged geometry. We find two different kinds of dangling bonds, in which the O-H stretching responsible for this mode is directed either to an empty space of a pore or towards a nearby CH4 molecule, with which some interaction takes place. The spectral characteristics of these two DB types are clearly different, and follow satisfactorily the pattern observed in experimental spectra. Estimated band strengths for these DB bands are given for the first time.Funds from the Spanish MINECO/FEDER FIS2016-77726-C3-1-P and C3-3-P projects are acknowledged. We are indebted to V. J. Herrero for technical assistance with the CASTEP calculations, performed at SGAI-CSIC.Maté, B.; Satorre, MÁ.; Escribano, R. (2021). On the spectral features of dangling bonds in CH4/H2O amorphous ice mixtures. Physical Chemistry Chemical Physics. 23(15):9532-9538. https://doi.org/10.1039/d1cp00291k95329538231

OPTICAL CONSTANTS AND BAND STRENGTHS OF CH4:C2H6 ICES IN THE NEAR- AND MID-INFRARED

[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.Funds have been provided for this research from the Spanish MINECO, Project FIS2013-48087-C2-1-P and FIS2013-48087-C2-2-P. G.M. acknowledges MINECO PhD grant BES-2014-069355. We are grateful to M. A. Moreno, J. Rodriguez, and I. Tanarro for technical help and to V. J. Herrero and I. Tanarro for discussions and manuscript preparation.Molpeceres, G.; Satorre, MÁ.; Ortigoso, J.; Millán Verdú, C.; Escribano, R.; Mate, B. (2016). OPTICAL CONSTANTS AND BAND STRENGTHS OF CH4:C2H6 ICES IN THE NEAR- AND MID-INFRARED. The Astrophysical Journal. 825(2). https://doi.org/10.3847/0004-637X/825/2/156S825

Densities, infrared band strengths, and optical constants of solid methanol

[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.Funds have been provided for this research by the Spanish MINECO, Project FIS2016-77726-C3-1-P and FIS2016-77726-C3-3-P. German Molpeceres acknowledges MINECO PhD grant BES-2014-069355. We are grateful to R. Escribano for helpful discussions. Our skillful technicians C. Santonja, M. A. Moreno, and J. Rodriguez are also gratefully acknowledged.Luna Molina, R.; Molpeceres, G.; Ortigoso, J.; Satorre, MÁ.; Domingo Beltran, M.; Maté, B. (2018). Densities, infrared band strengths, and optical constants of solid methanol. Astronomy and Astrophysics. 617:1-9. https://doi.org/10.1051/0004-6361/201833463S19617Boogert, A. C. A., Pontoppidan, K. M., Knez, C., Lahuis, F., Kessler‐Silacci, J., van Dishoeck, E. F., … Stapelfeldt, K. R. (2008). The c2dSpitzerSpectroscopic Survey of Ices around Low‐Mass Young Stellar Objects. I. H2O and the 5–8 μm Bands1,2. The Astrophysical Journal, 678(2), 985-1004. doi:10.1086/533425Boogert, A. C. A., Gerakines, P. A., & Whittet, D. C. B. (2015). Observations of the Icy Universe. Annual Review of Astronomy and Astrophysics, 53(1), 541-581. doi:10.1146/annurev-astro-082214-122348Bossa, J.-B., Maté, B., Fransen, C., Cazaux, S., Pilling, S., Rocha, W. R. M., … Linnartz, H. (2015). POROSITY AND BAND-STRENGTH MEASUREMENTS OF MULTI-PHASE COMPOSITE ICES. The Astrophysical Journal, 814(1), 47. doi:10.1088/0004-637x/814/1/47Bottinelli, S., Boogert, A. C. A., Bouwman, J., Beckwith, M., van Dishoeck, E. F., Öberg, K. I., … Lahuis, F. (2010). THE c2dSPITZERSPECTROSCOPIC SURVEY OF ICES AROUND LOW-MASS YOUNG STELLAR OBJECTS. IV. NH3AND CH3OH. The Astrophysical Journal, 718(2), 1100-1117. doi:10.1088/0004-637x/718/2/1100Bouilloud, M., Fray, N., Bénilan, Y., Cottin, H., Gazeau, M.-C., & Jolly, A. (2015). Bibliographic review and new measurements of the infrared band strengths of pure molecules at 25 K: H2O, CO2, CO, CH4, NH3, CH3OH, HCOOH and H2CO. Monthly Notices of the Royal Astronomical Society, 451(2), 2145-2160. doi:10.1093/mnras/stv1021Cazaux, S., Bossa, J.-B., Linnartz, H., & Tielens, A. G. G. M. (2014). Pore evolution in interstellar ice analogues. Astronomy & Astrophysics, 573, A16. doi:10.1051/0004-6361/201424466Dohnálek, Z., Kimmel, G. A., Ayotte, P., Smith, R. S., & Kay, B. D. (2003). The deposition angle-dependent density of amorphous solid water films. The Journal of Chemical Physics, 118(1), 364-372. doi:10.1063/1.1525805Drabek-Maunder E., Greaves J., Fraser H. J., Clements D. L., & Alconcel L. N. 2017, Int. J. Astrobiol., DOI: 10.1017/S1473550417000428Gálvez, O., Maté, B., Martín-Llorente, B., Herrero, V. J., & Escribano, R. (2009). Phases of Solid Methanol. The Journal of Physical Chemistry A, 113(14), 3321-3329. doi:10.1021/jp810239rGerakines, P. A., Bray, J. J., Davis, A., & Richey, C. R. (2005). The Strengths of Near‐Infrared Absorption Features Relevant to Interstellar and Planetary Ices. The Astrophysical Journal, 620(2), 1140-1150. doi:10.1086/427166Hodyss, R., Parkinson, C. D., Johnson, P. V., Stern, J. V., Goguen, J. D., Yung, Y. L., & Kanik, I. (2009). Methanol on Enceladus. Geophysical Research Letters, 36(17). doi:10.1029/2009gl039336Hudgins, D. M., Sandford, S. A., Allamandola, L. J., & Tielens, A. G. G. M. (1993). Mid- and far-infrared spectroscopy of ices - Optical constants and integrated absorbances. The Astrophysical Journal Supplement Series, 86, 713. doi:10.1086/191796Hudson, R. L., Ferrante, R. F., & Moore, M. H. (2014). Infrared spectra and optical constants of astronomical ices: I. Amorphous and crystalline acetylene. Icarus, 228, 276-287. doi:10.1016/j.icarus.2013.08.029Ioppolo, S., van Boheemen, Y., Cuppen, H. M., van Dishoeck, E. F., & Linnartz, H. (2011). Surface formation of CO2 ice at low temperatures. Monthly Notices of the Royal Astronomical Society, 413(3), 2281-2287. doi:10.1111/j.1365-2966.2011.18306.xIsokoski, K., Bossa, J.-B., Triemstra, T., & Linnartz, H. (2014). Porosity and thermal collapse measurements of H2O, CH3OH, CO2, and H2O:CO2 ices. Physical Chemistry Chemical Physics, 16(8), 3456. doi:10.1039/c3cp54481hMaté, B., Gálvez, Ó., Herrero, V. J., & Escribano, R. (2008). INFRARED SPECTRA AND THERMODYNAMIC PROPERTIES OF CO2/METHANOL ICES. The Astrophysical Journal, 690(1), 486-495. doi:10.1088/0004-637x/690/1/486Merlin, F., Quirico, E., Barucci, M. A., & de Bergh, C. (2012). Methanol ice on the surface of minor bodies in the solar system. Astronomy & Astrophysics, 544, A20. doi:10.1051/0004-6361/201219181Molpeceres, G., Satorre, M. A., Ortigoso, J., Millán, C., Escribano, R., & Maté, B. (2016). OPTICAL CONSTANTS AND BAND STRENGTHS OF CH4:C2H6ICES IN THE NEAR- AND MID-INFRARED. The Astrophysical Journal, 825(2), 156. doi:10.3847/0004-637x/825/2/156Öberg, K. I. (2016). Photochemistry and Astrochemistry: Photochemical Pathways to Interstellar Complex Organic Molecules. Chemical Reviews, 116(17), 9631-9663. doi:10.1021/acs.chemrev.5b00694Pontoppidan, K. M., Dartois, E., van Dishoeck, E. F., Thi, W.-F., & d’ Hendecourt, L. (2003). Detection of abundant solid methanol toward young low mass stars. Astronomy & Astrophysics, 404(1), L17-L20. doi:10.1051/0004-6361:20030617Sandford, S. A., & Allamandola, L. J. (1993). Condensation and vaporization studies of CH3OH and NH3 ices: Major implications for astrochemistry. The Astrophysical Journal, 417, 815. doi:10.1086/173362Satorre, M. Á., Domingo, M., Millán, C., Luna, R., Vilaplana, R., & Santonja, C. (2008). Density of , and ices at different temperatures of deposition. Planetary and Space Science, 56(13), 1748-1752. doi:10.1016/j.pss.2008.07.015Satorre, M. Á., Leliwa-Kopystynski, J., Santonja, C., & Luna, R. (2013). Refractive index and density of ammonia ice at different temperatures of deposition. Icarus, 225(1), 703-708. doi:10.1016/j.icarus.2013.04.023Satorre, M. Á., Millán, C., Molpeceres, G., Luna, R., Maté, B., Domingo, M., … Santonja, C. (2017). Densities and refractive indices of ethane and ethylene at astrophysically relevant temperatures. Icarus, 296, 179-182. doi:10.1016/j.icarus.2017.05.005Sauerbrey, G. (1959). Verwendung von Schwingquarzen zur W�gung d�nner Schichten und zur Mikrow�gung. Zeitschrift f�r Physik, 155(2), 206-222. doi:10.1007/bf01337937Torrie, B. H., Weng, S.-X., & Powell, B. M. (1989). Structure of the α-phase of solid methanol. Molecular Physics, 67(3), 575-581. doi:10.1080/00268978900101291Watanabe, N., & Kouchi, A. (2002). Efficient Formation of Formaldehyde and Methanol by the Addition of Hydrogen Atoms to CO in H[TINF]2[/TINF]O-CO Ice at 10 K. The Astrophysical Journal, 571(2), L173-L176. doi:10.1086/341412Weast R. 1972, Handbook of Chemistry and Physics, 53rd edn. (Cleveland: Chemical Rubber Co.), 155Zanchet, A., Rodríguez-Lazcano, Y., Gálvez, Ó., Herrero, V. J., Escribano, R., & Maté, B. (2013). OPTICAL CONSTANTS OF NH3AND NH3:N2AMORPHOUS ICES IN THE NEAR-INFRARED AND MID-INFRARED REGIONS. The Astrophysical Journal, 777(1), 26. doi:10.1088/0004-637x/777/1/2

Density and Refractive Index of Carbon Monoxide Ice at Different Temperatures

[EN] This paper is intended to study the density and the refractive index of the solid carbon monoxide in the interval 13-28 K to improve our understanding of the dynamics in the astrophysical environments where they are present. A series of deposition experiments have been performed under high vacuum conditions to study the properties of this ice under astrophysical conditions. Ice density has been experimentally calculated at different deposition temperatures of astrophysical interest, which complement the scarce values present in the literature. The refractive index has also been experimentally determined. The data have been used to obtain an experimental relationship between refractive index and density. Values of density are necessary to interpret observations of astrophysical objects or to design irradiation experiments to understand how irradiation affects ices present in these objects. The experimental relationship found between density and refractive index allows us to estimate density from a known refractive index, even for temperatures not reached using our experimental setup.Funds have been provided for this research by the Spanish MINECO, Project PID2020-118974GB-C22.Luna Molina, R.; Millán, C.; Domingo Beltran, M.; Santonja Moltó, MDC.; Satorre, MÁ. (2022). Density and Refractive Index of Carbon Monoxide Ice at Different Temperatures. The Astrophysical Journal. 935(2):1-6. https://doi.org/10.3847/1538-4357/ac800116935

An experimental test for effective medium approximations (EMAs) Porosity determination for ices of astrophysical interest

[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.Funds have been provided for this research by the Spanish MINECO, Project FIS2016-77726-C3-3-P.Millán Verdú, C.; Santonja Moltó, MDC.; Domingo Beltran, M.; Luna Molina, R.; Satorre, MÁ. (2019). An experimental test for effective medium approximations (EMAs) Porosity determination for ices of astrophysical interest. Astronomy and Astrophysics. 628(A63):1-5. https://doi.org/10.1051/0004-6361/201935153S15628A63Aikawa, Y., Wakelam, V., Garrod, R. T., & Herbst, E. (2008). Molecular Evolution and Star Formation: From Prestellar Cores to Protostellar Cores. The Astrophysical Journal, 674(2), 984-996. doi:10.1086/524096Bartels-Rausch, T., Bergeron, V., Cartwright, J. H. E., Escribano, R., Finney, J. L., Grothe, H., … Uras-Aytemiz, N. (2012). Ice structures, patterns, and processes: A view across the icefields. Reviews of Modern Physics, 84(2), 885-944. doi:10.1103/revmodphys.84.885Born M., & Wolf E. 1999, Principles of Optics: Electromagnetic Theory of Propagation, Interference and Diffraction of Light (Cambridge: Cambridge University Press)Bossa, J.-B., Isokoski, K., Paardekooper, D. M., Bonnin, M., van der Linden, E. P., Triemstra, T., … Linnartz, H. (2014). Porosity measurements of interstellar ice mixtures using optical laser interference and extended effective medium approximations. Astronomy & Astrophysics, 561, A136. doi:10.1051/0004-6361/201322549Brovchenko, I., & Oleinikova, A. (2006). Four phases of amorphous water: Simulations versus experiment. The Journal of Chemical Physics, 124(16), 164505. doi:10.1063/1.2194906Cazaux, S., Bossa, J.-B., Linnartz, H., & Tielens, A. G. G. M. (2014). Pore evolution in interstellar ice analogues. Astronomy & Astrophysics, 573, A16. doi:10.1051/0004-6361/201424466Isokoski, K., Bossa, J.-B., Triemstra, T., & Linnartz, H. (2014). Porosity and thermal collapse measurements of H2O, CH3OH, CO2, and H2O:CO2 ices. Physical Chemistry Chemical Physics, 16(8), 3456. doi:10.1039/c3cp54481hKeane, J. V., Boogert, A. C. A., Tielens, A. G. G. M., Ehrenfreund, P., & Schutte, W. A. (2001). Bands of solid CO$_\mathsf{2}$ in the 2-3μm spectrum of S 140:IRS1. Astronomy & Astrophysics, 375(3), L43-L46. doi:10.1051/0004-6361:20010977Loeffler, M. J., Moore, M. H., & Gerakines, P. A. (2016). THE EFFECTS OF EXPERIMENTAL CONDITIONS ON THE REFRACTIVE INDEX AND DENSITY OF LOW-TEMPERATURE ICES: SOLID CARBON DIOXIDE. The Astrophysical Journal, 827(2), 98. doi:10.3847/0004-637x/827/2/98Lorentz, H. A. (1880). Ueber die Beziehung zwischen der Fortpflanzungsgeschwindigkeit des Lichtes und der Körperdichte. Annalen der Physik und Chemie, 245(4), 641-665. doi:10.1002/andp.18802450406Lorenz, L. (1880). Ueber die Refractionsconstante. Annalen der Physik und Chemie, 247(9), 70-103. doi:10.1002/andp.18802470905Luna, R., Millán, C., Domingo, M., & Satorre, M. Á. (2008). Thermal desorption of CH4 retained in CO2 ice. Astrophysics and Space Science, 314(1-3), 113-119. doi:10.1007/s10509-008-9746-2Markel, V. A. (2016). Introduction to the Maxwell Garnett approximation: tutorial. Journal of the Optical Society of America A, 33(7), 1244. doi:10.1364/josaa.33.001244Markel, V. A. (2016). Maxwell Garnett approximation (advanced topics): tutorial. Journal of the Optical Society of America A, 33(11), 2237. doi:10.1364/josaa.33.002237XII. Colours in metal glasses and in metallic films. (1904). Philosophical Transactions of the Royal Society of London. Series A, Containing Papers of a Mathematical or Physical Character, 203(359-371), 385-420. doi:10.1098/rsta.1904.0024VII. Colours in metal glasses, in metallic films, and in metallic solutions.—II. (1906). Philosophical Transactions of the Royal Society of London. Series A, Containing Papers of a Mathematical or Physical Character, 205(387-401), 237-288. doi:10.1098/rsta.1906.0007Palumbo, M. E., Baratta, G. A., Leto, G., & Strazzulla, G. (2010). H bonds in astrophysical ices. Journal of Molecular Structure, 972(1-3), 64-67. doi:10.1016/j.molstruc.2009.12.017Rodgers, S. D., & Charnley, S. B. (2003). Chemical Evolution in Protostellar Envelopes: Cocoon Chemistry. The Astrophysical Journal, 585(1), 355-371. doi:10.1086/345497Rowland, B., Fisher, M., & Devlin, J. P. (1991). Probing icy surfaces with the dangling‐OH‐mode absorption: Large ice clusters and microporous amorphous ice. The Journal of Chemical Physics, 95(2), 1378-1384. doi:10.1063/1.461119Satorre, M. Á., Domingo, M., Millán, C., Luna, R., Vilaplana, R., & Santonja, C. (2008). Density of , and ices at different temperatures of deposition. Planetary and Space Science, 56(13), 1748-1752. doi:10.1016/j.pss.2008.07.015Satorre M., Luna R., Millán C., Domingo M., & Santonja C. 2018, in Astrophys. Space Sci. Lib., eds. Muñoz Caro G. M., & Escribano R., 451, 51Sauerbrey, G. (1959). Verwendung von Schwingquarzen zur W�gung d�nner Schichten und zur Mikrow�gung. Zeitschrift f�r Physik, 155(2), 206-222. doi:10.1007/bf01337937Schulze, W., & Abe, H. (1980). Density, refractive index and sorption capacity of solid CO2 layers. Chemical Physics, 52(3), 381-388. doi:10.1016/0301-0104(80)85240-2Stroud, D. (1998). The effective medium approximations: Some recent developments. Superlattices and Microstructures, 23(3-4), 567-573. doi:10.1006/spmi.1997.0524Viti, S., Collings, M. P., Dever, J. W., McCoustra, M. R. S., & Williams, D. A. (2004). Evaporation of ices near massive stars: models based on laboratory temperature programmed desorption data. Monthly Notices of the Royal Astronomical Society, 354(4), 1141-1145. doi:10.1111/j.1365-2966.2004.08273.xWarren, S. G. (1986). Optical constants of carbon dioxide ice. Applied Optics, 25(16), 2650. doi:10.1364/ao.25.002650Westley, M. S., Baratta, G. A., & Baragiola, R. A. (1998). Density and index of refraction of water ice films vapor deposited at low temperatures. The Journal of Chemical Physics, 108(8), 3321-3326. doi:10.1063/1.47573

Variación de la cromaticidad con la temperatura de unión en LEDs de alta potencia

[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.Patirnac, S.; Satorre, MÁ.; Gilabert Pérez, EJ. (2013). Variación de la cromaticidad con la temperatura de unión en LEDs de alta potencia. Compobell, S.L. http://hdl.handle.net/10251/74017

Study of the frequency factor in the thermal desorption of astrophysical ice analogs: CH4, C2H4, C2H6, CH3OH, CO, CO2, H2O and N2

[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.This work was supported by the Plan Nacional FIS2013-48087-C2-2-P and FIS2016-77726-C3-3-P of the Ministerio de Economia y Competitividad (co-financed by FEDER funds).Luna Molina, R.; Domingo Beltran, M.; Millán Verdú, C.; Santonja Moltó, MDC.; Satorre, MÁ. (2018). Study of the frequency factor in the thermal desorption of astrophysical ice analogs: CH4, C2H4, C2H6, CH3OH, CO, CO2, H2O and N2. Vacuum. 152:278-284. https://doi.org/10.1016/j.vacuum.2018.03.022S27828415

Experimental study of the frequency factor in the Polanyi-Wigner equation: the case of C2H6

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.2015.09.021The 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.This work was supported by the Plan Nacional FIS2013-48087-C2-2-P of the Ministerio de Economia y Competitividad.Luna Molina, R.; Millán Verdú, C.; Domingo Beltran, M.; Santonja Moltó, MDC.; Satorre, MÁ. (2015). Experimental study of the frequency factor in the Polanyi-Wigner equation: the case of C2H6. Vacuum. 122:154-160. https://doi.org/10.1016/j.vacuum.2015.09.021S15416012

Experimental Measurement of Carbon Dioxide Polarizability in the Solid State

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