Rafael Escribano | Universidad Politécnica de Madrid (original) (raw)

Papers by Rafael Escribano

Actas Del Vi Congreso Nacional De Evaluacion De Impacto Ambiental Vi Congreso Nacional De Evaluacion De Impacto Ambiental 06 04 2011 08 04 2012 Albacete Espana, 2011

Journal of Forest Research, 2011

We investigated how richness and composition of vascular plant species in the understory of a mix... more We investigated how richness and composition of vascular plant species in the understory of a mixed hardwood forest stand varied with respect to the abundance and composition of the overstory. The stand is in central Spain and represents the southernmost range of distribution of several tree and herbaceous species in Europe. Understory species were identified in 46 quadrats (0.25 m 2) where variables litter depth and light availability were measured. In addition, we estimated tree density, basal area, and percent basal area by tree species within 6-mradius areas around each plot. Species richness and composition were studied using path analysis and scaledependent geostatistical methods, respectively. We found that the relative abundance of certain trees species in the overstory was more important than total overstory abundance in explaining understory species richness. Richness decreased as soil litter depth increased, and soil litter increased as the relative proportion of Fagus sylvatica in the overstory increased, which accounted for a negative, indirect effect of Fagus sylvatica on richness. Regarding understory species composition, we found that some species distributed preferentially below certain tree species. For example, Mélica uniflora was most frequent below Fagus sylvatica and Quercus petraea while the increasing proportion of Q. pyrenaica in the overstory favored the

Urban E Territorio Urbanismo Paisaje Sostenibilidad Y Diseno Urbano Issn 2174 646x 2011 Vol 1 N 1, 2011

Tus alamedas músicas, tus aguas de sonata, tus rodales romeros, tus huellas de reata, el cáñamo a... more Tus alamedas músicas, tus aguas de sonata, tus rodales romeros, tus huellas de reata, el cáñamo apretado de mi humilde alpargata quisiera recorrerlas en total caminata. ………………………………. "Decir de La Rioja" GERARDO DIEGO RESUMEN El caminante que se adentra en el tramo riojano del camino de Santiago, encuentra ante sí 59 km de recorrido, a lo largo de los cuales tiene la opción de observar y transitar por una extraordinaria variedad de paisajes que se le ofrecen. Paisajes culturales y naturales, cotidianos y más singulares, cercanos y más alejados, paisajes que puede ver, percibir e intuir, que se muestran evidentes o más escondidos, que aparecen o a cuyo encuentro hay que partir, paisajes que nos reflejan algo más de lo que se ve, que se engrandecen con el paso del tiempo, que permanecen, sobreviven, pierden esencia o desaparecen. El Camino de Santiago es en La Rioja cultura, en gran parte asociada y reflejada en el paisaje. Se propone un recorrido por alguno de estos paisajes, cuyas características se desgranan tomando como hilo conductor algunos de los análisis llevados a cabo en

Estudios Geográficos

La superficie que actualmente ocupa el encinar en la Comunidad de Madrid es pequeña: alrededor de... more La superficie que actualmente ocupa el encinar en la Comunidad de Madrid es pequeña: alrededor del 14% de la superficie que de forma potencial podría ocupar. Esta escasa representación del encinar se encuentra, además, en diversos estados de conservación. En este artículo se presenta un intento de elaboración de una tipología de los encinares mediante el análisis multivariable de algunos datos de estructura y las especies botánicas que aparecen en ellos. [fr] Á présent lachênaie occupe le 14% de sa surface potentielle dans la Communauté de Madrid. Cette peu abondante representation a, en plus, plusieurs états de conservation. Dans cet article nous essayons d'elaborer une typologie des chênaies au moyen de l'analyse multivariable des données de la structure et le leur cortége botanique.

Heterogeneous reactions that take place over the surface of polar stratospheric cloud (PSC) parti... more Heterogeneous reactions that take place over the surface of polar stratospheric cloud (PSC) particles are thought to play an important role on stratospheric ozone depletion. Chlorine reservoir species, such as HCl and ClONO2, adsorbed on those particles, can be converted to reactive chlorine compounds, responsible for the destruction of ozone. The high temperature phase of nitric acid trihydrate (beta-NAT) is

Montes, 2007

... El cálculo de índices del paisaje con trascendencia ecológica en las muestras permitió analiz... more ... El cálculo de índices del paisaje con trascendencia ecológica en las muestras permitió analizar y comparar cuantitativamente la composición y configuración del paisaje de ambos Parques Naturales. RESUMEN Comparación de la estructura de los ...

Proceedings of the International Astronomical Union

Water-ice represents the largest fraction of icy mantles and it has been shown to be everywhere i... more Water-ice represents the largest fraction of icy mantles and it has been shown to be everywhere in the Universe. The relative average abundance of elemental deuterium to hydrogen is around 1.5 10-5 (1), and consequently, according to this value, different models predict abundance of HDO in the ice mantles of the order of 1 to 6% in dense cloud cores. Such concentrations could be accessible to observation by scrutiny from infrared space and terrestrial telescopes. Laboratory studies of deuterated icy materials which could serve as analogues for astrophysical particles are necessary to correctly interpret these spectra. During the last years, our group has employed infrared spectroscopy techniques to characterize different ice mixtures of astrophysical interest (see e.g. 2,3). In this presentation, we will show infrared spectra of D2O embedded in amorphous or crystalline H2O ice matrices at low temperatures (ranging from 14 K to 150 K). We have observed isotopic exchange at temperatur...

A study of the near infrared reflection and transmission spectra of ammonia-water ice mixtures gr... more A study of the near infrared reflection and transmission spectra of ammonia-water ice mixtures grown by vapor deposition at various temperatures and with different NH3/H2O ratios has been conducted. Variations in positions and widths of the 2.2 μm and 2.0 μm bands of NH3 and of the 2.0 μm and 1.65 μm bands of H2O in the mixtures will be discussed. These findings are expected to be relevant for the comparison with astrophysical data to estimate the concentration of ammonia in outer solar system ices, and their temperature.

Physical chemistry chemical physics : PCCP, Jan 21, 2014

The symmetric stretching vibration (breathing mode) of methane is forbidden in the infrared spect... more The symmetric stretching vibration (breathing mode) of methane is forbidden in the infrared spectra of gases. However, it has been observed in the spectra of low-pressure ice mixtures of methane and water, studied as models for astronomical ices. We investigate the possible origin of the activation of this mode by means of solid state calculations of amorphous water (ASW) samples into which methane molecules are introduced. Activation is predicted either by the interaction of the CH4 and H2O molecules in pore walls or via a strong mode coupling that takes place between the breathing mode of CH4 and the O-H stretching mode of H2O when both vibrations coincide in frequency. These two mechanisms would be favored for low-density or high density ASW, respectively. A possible experimental observation of this activation in compact ASW is discussed.

The relevance of nitric acid hydrates in stratospheric processes has prompted a large number of i... more The relevance of nitric acid hydrates in stratospheric processes has prompted a large number of investigations on the structure and physicochemical properties of these species. We are carrying out in our lab a study on the spectroscopy of crystals of nitric acid and the mono-, di- and trihydrates, NAM, NAD and NAT, respectively, as a first step to addressing more

Proceedings of The International Astronomical Union, 2011

The identification of interstellar biomolecules is a subject of great interest, as they may provi... more The identification of interstellar biomolecules is a subject of great interest, as they may provide important insights into the history of the solar system and the origin of life on Earth. Amino acids have been found in Solar System bodies and meteorites. The simplest of the amino acids and the most vastly studied and searched is glycine, NH2CH2COOH. It has

Ices of mixtures of H2O and CO2 can be found in different astrophysical environments, like cometa... more Ices of mixtures of H2O and CO2 can be found in different astrophysical environments, like cometary nuclei or making part of solar system bodies. Water and carbon dioxide can associate in different ways in the solid state, depending on the temperature, relative concentration and process of formation of the ice. Infrared spectroscopy provides a sensitive tool to study different structures

The Journal of Physical Chemistry A, 2000

The geometrical structure, binding energy, and vibrational spectra of small clusters of HOCl and ... more The geometrical structure, binding energy, and vibrational spectra of small clusters of HOCl and water molecules, HOCl(H 2 O) n , n) 1-4, have been investigated at the MP2 level of theory, using triple-Z, 6-311++G(d,p), basis sets. The ab initio results predict for the clusters an almost planar ring skeleton, made up of the O atoms and one H atom from each molecule, linked by hydrogen bonding to the next oxygen. The species with one water unit presents two almost equally stable conformers, syn and anti, in agreement with previous calculations. Two stable structures have also been found for clusters with three and four molecules of water, one where the H atom of the HOCl molecule makes part of the ring, and another one in which the Cl atom is in the ring. The more stable in either case is found to be the H-in molecule, with a difference of 35.6 kJ/mol in optimized energy. The predicted spectra for these two species are very different. As the number of water units increases, the corresponding clusters become more stable, and a number of physical effects is predicted. The more important one is the increase in the intramolecular O-H bond length, which is responsible for a large reduction in the wavenumber of the corresponding O-H vibration. The results indicate the formation of hydrogen bonds and a partial proton transfer from HOCl to the water ring structure. In a parallel calculation, water clusters, (H 2 O) n , n) 1-5, have also been investigated. Our results agree well with those of previous authors.

The Journal of Physical Chemistry A, 2004

... Fernández-Torre* and Rafael Escribano. Instituto de Estructura de la Materia, CSIC, Serrano 1... more ... Fernández-Torre* and Rafael Escribano. Instituto de Estructura de la Materia, CSIC, Serrano 123, 28006 Madrid, Spain. Tom Archer, JM Pruneda, and Emilio Artacho. Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK. J. Phys. ...

The Journal of Physical Chemistry A, 2008

Ice mixtures of CO 2 and H 2 O are studied using Fourier transform reflection-absorption infrared... more Ice mixtures of CO 2 and H 2 O are studied using Fourier transform reflection-absorption infrared (RAIR) spectroscopy. Mixtures are prepared by sequential deposition or co-deposition of the two components from the gas phase onto an Al plate kept at 87 K inside a low-pressure chamber. Two CO 2 structures are found in most experiments: a crystalline form similar to pure CO 2 , which evaporates when warming at 105 K, and a noncrystalline species which remains embedded in amorphous water ice after warming. Significant spectral variations are found depending on the deposition method and the thickness of the solid. Features characteristic of the RAIR technique appear in the spectral regions of the normal modes of the bending and asymmetric stretching CO 2 vibrations. Simulations using Fresnel theory and Mie scattering are carried out with acceptable agreement with the experimental spectra of solids of variable thickness, from ∼1 µm to the limit of nanoparticles. Theoretical calculations of a pure CO 2 crystal are performed. The relaxed geometry of the solid and its vibrational spectrum are determined and compared to the experimental results.

The Astrophysical Journal, 2008

Ices of mixtures of carbon dioxide and methanol have been studied in a range of temperatures rele... more Ices of mixtures of carbon dioxide and methanol have been studied in a range of temperatures relevant for starforming regions, comets, polar caps of planets and satellites, and other solar system bodies. We have performed temperature-programmed desorption measurements and recorded IR spectra of various types of samples. The presence of two slightly different structures of CO 2 is manifest. A distorted CO 2 structure is characterized by bandshifts between 5 cm −1 (ν 3) and 10 cm −1 (ν 2) with respect to normal CO 2. If the samples are heated above 130 K, the distorted CO 2 sublimates and only the normal structure remains. The latter can stay trapped until the sublimation of crystalline methanol (150 K). The desorption energy (E d ∼ 20 kJ mol −1) of CO 2 from methanol ice, and the specific adsorption surface area (6 m 2 g −1) of amorphous CH 3 OH ice, have been determined. CO 2 does not penetrate into crystalline ice. Whereas the desorption energy is similar to that of CO 2 /H 2 O samples, the specific surface of methanol is much smaller than that of amorphous solid water (ASW). The interaction of CO 2 molecules with water and methanol is similar but ices of CH 3 OH are much less porous than ASW. The inclusion of CO 2 into previously formed ices containing these two species would take place preferentially into ASW. However, in processes of simultaneous deposition, methanol ice can admit a larger amount of CO 2 than water ice. CO 2 /CH 3 OH ices formed by simultaneous deposition admit two orders of magnitude more CO 2 than sequentially deposited ices. These findings can have direct relevance to the interpretation of observations from protostellar environments (e.g., RAFGL7009S) and comet nuclei.

The Astrophysical Journal, 2009

The 6.85 μm band observed in the spectra of young stellar objects has been analyzed recently and ... more The 6.85 μm band observed in the spectra of young stellar objects has been analyzed recently and the most usually accepted assignment to the ν 4 bending mode of NH 4 + is still under debate. We present here a laboratory study of frozen solutions of NH 4 + Cl − in water in an astrophysical range of concentrations and temperatures. The samples are prepared by hyper-quenching of liquid droplets on a cold substrate. The ν 4 band of NH 4 + , which is very strong in the pure crystal and in the liquid solution at ambient temperature, becomes almost blurred in IR spectra of the frozen solution. The effect of the chlorine anion is expected to be of little relevance in this study. The experimental results are supported by theoretical calculations, which predict a broad range of weak ν 4 features for amorphous samples containing different ammonium environments. The present results indicate that the ammonium ion surrounded by water molecules only cannot suffice to explain this spectral feature. This paper contributes with new evidence to the discussion on the assignment of the 6.85 μm band.

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2005

Review of Scientific Instruments, 2002

A simple experimental setup for the production of cold samples for spectroscopy is described. The... more A simple experimental setup for the production of cold samples for spectroscopy is described. The samples are deposited under vacuum on a cold metallic surface whose temperature is controlled between 80 and 323 K by varying the heat flow balance between a liquid nitrogen reservoir and a power transistor. Tests of temperature stability and thermal inertia, as well as a set of reflectionabsorption infrared and thermal desorption spectra, are reported as a demonstration of the performance of the system.

Proceedings of the National Academy of Sciences, 2013

Carbon dioxide (CO 2 ) is one of the most relevant and abundant species in astrophysical and atmo... more Carbon dioxide (CO 2 ) is one of the most relevant and abundant species in astrophysical and atmospheric media. In particular, CO 2 ice is present in several solar system bodies, as well as in interstellar and circumstellar ice mantles. The amount of CO 2 in ice mantles and the presence of pure CO 2 ice are significant indicators of the temperature history of dust in protostars. It is therefore important to know if CO 2 is mixed with other molecules in the ice matrix or segregated and whether it is present in an amorphous or crystalline form. We apply a multidisciplinary approach involving IR spectroscopy in the laboratory, theoretical modeling of solid structures, and comparison with astronomical observations. We generate an unprecedented highly amorphous CO 2 ice and study its crystallization both by thermal annealing and by slow accumulation of monolayers from the gas phase under an ultrahigh vacuum. Structural changes are followed by IR spectroscopy. We also devise theoretical m...