Person:
García Baonza, Valentín

First Name

Valentín

Last Name

García Baonza

URI

https://hdl.handle.net/20.500.14352/76144

Affiliation

Universidad Complutense de Madrid

Faculty / Institute

Ciencias Químicas

Area

Química Física

Identifiers

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Now showing 1 - 10 of 13

Anharmonicity effects in the frictionlike mode of graphite
(Physical Review B, 2016) C. Menéndez; Lobato Fernández, Álvaro; D. Abbasi-Pérez; J. Fernández-Núñez; J. M. Recio; García Baonza, Valentín
Theoretical (DFT) and experimental (Raman and FTIR) spectroscopic study on communic acids, main components of fossil resins
(Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2019) Oscar R. Montoro; Tortajada Pérez, José; Lobato Fernández, Álvaro; García Baonza, Valentín; Taravillo Corralo, Mercedes
Envejecimiento con radiación UV de una variedad de cartón pluma neutro: Estudio de su evolución cromática y composición
(Optica Pura y Aplicada, 2010) Roja, J. M. de la; Chercoles, R.; Gómez, M.; San Andrés Moya, Margarita; García Baonza, Valentín
Los materiales utilizados en el ámbito de la conservación del Patrimonio deben ser previamente investigados para conocer su composición y comportamiento con el envejecimiento. Por ello, resulta imprescindible su caracterización analítica, identificar los cambios que ésta pueda experimentar a largo plazo y las consecuencias sobre sus propiedades iniciales. En este artículo se presentan los resultados correspondientes al estudio de una variedad de cartón pluma (cartón pluma neutro), material laminar multicapa, constituido por un núcleo interno espumado de poliestireno y recubierto de cartulina de celulosa pura que contiene una carga de calcita. Ambos componentes (cartulina y núcleo) han sido sometidos a envejecimiento artificial acelerado bajo la acción de radiación UV y, en las condiciones ensayadas, presentan un comportamiento muy distinto. La cartulina es prácticamente estable en su composición y color (E00=0,470,20), mientras que el núcleo espumado de poliestireno experimenta una importante oxidación que repercute en su color (E00=19,100,49). Los análisis FTIR-ATR constatan la formación de grupos oxigenados, especialmente grupos carbonilo (C=O) cuya presencia aumenta con el envejecimiento. La intensidad de la banda asignada a este grupo y el E00 experimentado se relacionan mediante una curva de regresión no lineal, que muestra la evolución de la alteración del poli(estireno).
Computational Modeling of Tensile Stress Effects on the Structure and Stability of Prototypical Covalent and Layered Materials
(Nanomaterials, 2019) Chorfi, Hocine; Lobato Fernández, Álvaro; Boudjada, Fahima; Salvadó, Miguel A.; Franco, Ruth; García Baonza, Valentín; Recio, J. Manuel
Understanding the stability limit of crystalline materials under variable tensile stress conditions is of capital interest for technological applications. In this study, we present results from first-principles density functional theory calculations that quantitatively account for the response of selected covalent and layered materials to general stress conditions. In particular, we have evaluated the ideal strength along the main crystallographic directions of 3C and 2H polytypes of SiC, hexagonal ABA stacking of graphite and 2H-MoS 2 . Transverse superimposed stress on the tensile stress was taken into account in order to evaluate how the critical strength is affected by these multi-load conditions. In general, increasing transverse stress from negative to positive values leads to the expected decreasing of the critical strength. Few exceptions found in the compressive stress region correlate with the trends in the density of bonds along the directions with the unexpected behavior. In addition, we propose a modified spinodal equation of state able to accurately describe the calculated stress–strain curves. This analytical function is of general use and can also be applied to experimental data anticipating critical strengths and strain values, and for providing information on the energy stored in tensile stress processes.
Linear, Non-Conjugated Cyclic and Conjugated Cyclic Paraphenylene under Pressure
(Molecules, 2019) Peña-Álvarez, Miriam; Fanetti, Samuele; Falsini, Naomi; Novelli, Giulia; Casado, Juan; García Baonza, Valentín; Taravillo Corralo, Mercedes; Parsons, Simon; Bini, Roberto; Citroni, Margherita
The n-paraphenylene family comprises chains of phenylene units linked together by C-C bonds that are between single- and double-bonded, and where n corresponds to the number of phenylene units. In this work, we compare the response of the optical properties of different phenylene arrangements. We study linear chains (LPP), cyclic systems (CPPs), and non-conjugated cyclic systems with two hydrogenated phenylenes (H4[n]CPP). Particularly, the systems of interest in this work are [6]LPP, [12]- and [6]CPP and H4[6]CPP. This work combines Raman and infrared spectroscopies with absorption and fluorescence (one- and two-photon excitations) measured as a function of pressure up to maximum of about 25 GPa. Unprecedented crystallographic pressure-dependent results are shown on H4[n]CPP, revealing intramolecular π-π interactions upon compression. These intramolecular interactions justify the H4[n]CPP singular optical properties with increasing fluorescence lifetime as a function of pressure.
Local and solvation pressures in aqueous solutions of ethylenediamine probed by Raman spectroscopy
(Physical Chemistry Chemical Physics, 2016) Cáceres Alonso, María Mercedes; Lobato Fernández, Álvaro; Nubia Judith Mendoza; Laura Jimenez Bonales; García Baonza, Valentín
Raman spectra of 1,2-ethylenediamine (EDA) in aqueous solutions are used to demonstrate that EDA molecules experience an anti–gauche conformational change resulting from the interactions with water. The observed Raman shift reveals a compressive (hydrophobic) effect of water on both methylene and amino groups of EDA. Raman spectra of EDA at high pressures are used as reference to quantify the intermolecular EDA–H2O interactions in terms of local pressures. These results are compared with macroscopic solvation pressures calculated from the cohesive energy parameter. We compare and discuss all our observations with available computational and experimental studies.
The self-absorption phenomenon in quantitative Raman spectroscopy and how to correct its effects
(Microchemical Journal, 2018) L. M. Uriarte; L.J. Bonales; J. Dubessy; Lobato Fernández, Álvaro; García Baonza, Valentín; Cáceres Alonso, María Mercedes
When the wavelength of the Raman scattered light coincides with the absorption spectrum of the sample, a phenomenon known as Raman self-absorption occurs. If the absorption wavelength range matches completely with the Raman wavenumber range for a given excitation line (high absorption), this process causes spectra with poor signal-to-noise-ratio, making the acquisition nearly impossible. When the absorption of the sample and the Raman scattered are partially coincident (low absorption), smaller modifications in the band-profile of the Raman spectrum are expected difficult to be detected. If a different excitation wavelength is available in order to avoid or minimize this phenomenon, a correction method is customary. The correction methods developed so far in quantitative analysis are still very complex and require the knowledge of several sampling parameters. In this work, we present a very simple but reliable method based on the Beer-Lambert law to correct low self-absorption effects. This method uses simple concepts, a straightforward methodology and the concentration of the Raman active component in the liquid matrix is the only parameter required to perform the correction. This method may be extremely useful in different fields in which Raman spectroscopy is used to obtain molecular and structural information from a band profile analysis. As an example, the method is applied here to successfully correct the Raman spectra of different CuSO4 aqueous solutions excited at 532nm.
Chemical pressure–chemical knowledge: squeezing bonds and lone pairs within the valence shell electron pair repulsion model
(Physical Chemistry Chemical Physics, 2019) Lobato Fernández, Álvaro; H. H. Osman; M. A. Salvadó; Taravillo Corralo, Mercedes; García Baonza, Valentín; J. M. Recio
The valence shell electron pair repulsion (VSEPR) model is a demanding testbed for modern chemical bonding formalisms. The challenge consists in providing reliable quantum mechanical interpretations of how chemical concepts such as bonds, lone pairs, electronegativity, or hypervalence influence (or modulate) molecular geometries. Several schemes have been developed thus far to visualize and characterize these effects; however, to the best of our knowledge, no scheme has yet incorporated the analysis of the premises derived from the ligand close-packing (LCP) extension of the VSEPR model. Within the LCP framework, the activity of the lone pairs of the central atom and ligand–ligand repulsions constitute the two key features necessary to explain certain controversial molecular geometries that do not conform to the VSEPR rules. Considering the dynamical picture obtained when electron local forces at different nuclear configurations are evaluated from first-principles calculations, we investigate the chemical pressure distributions in a variety of molecular systems, namely, electron-deficient molecules (BeH2, BH3, BF3), several AX3 series (A: N, P, As; X: H, F, Cl), SO2, ethylene, SF4, ClF3, XeF2, and nonequilibrium configurations of water and ammonia. Our chemical pressure maps clearly reveal space regions that are totally consistent with the molecular and electronic geometries predicted by VSEPR and provide a quantitative correlation between the lone pair activity of the central atom and electronegativity of ligands, which are in agreement with the LCP model. Moreover, the analysis of the kinetic and potential energy contributions to the chemical pressure allows us to provide simple explanations on the connection between ligand electronegativity and electrophilic/nucleophilic character of the molecules, with interesting implications in their potential reactivity. NH3, NF3, SO2, BF3, and the inversion barrier of AX3 molecules are selected to illustrate our findings.
Infrared spectroscopic study of the formation of fossil resin analogs with temperature using trans-communic acid as precursor
(Microchemical Journal, 2018) Óscar R. Montoro; Lobato Fernández, Álvaro; García Baonza, Valentín; Taravillo Corralo, Mercedes
For million years resin exudates have undergone chemical alterations by heat, pressure, radiation, water, oxygen, microorganisms, and have suffered processes of sedimentation and diagenesis. These agents have affected the organic functional groups present in the terpenes of the resins, giving rise to what we nowadays know as fossil resins. In this work, we try to get further insight in the chemical formation of fossil resins. As the simulation of the natural process is quite complex, we have focused on the temperature induced reactivity of the trans-communic acid, the main component of the Class I resins. Using this terpene derivate as a very basic model of a resin exudate, we have monitored their thermal changes by infrared spectroscopy, Differential Scanning Calorimetry and Thermogravimetric Analysis within the range of 25 to 340 °C. The temperature-induced transformation, both in presence and absence of inert atmosphere, is discussed on the basis of the reactivity of the conjugated double-bond, the exocyclic bond and the carboxylic acid group present in the trans-communic acid. The results obtained in these series of experiments agree with the maturation scheme accepted in the literature for natural resins, i.e. an initial cross-linked polymerization and a subsequent maturation reaction. From combined DSC/TGA and infrared spectroscopy results, we conclude that chemical changes produced in the trans-communic acid in the range 130–175 °C may mimic the initial polymerization-like process in the natural resins, whereas those produced between 180 and 340 °C seem to correspond to the maturation pathways described in the literature for fossil resins Class Ib. Spectral assignment of the most relevant infrared-active modes of the trans-communic acid at 25 °C is also provided with the aid of Density Functional Theory calculations.
Project number: 242
Laboratorio integrado de prácticas de simulación de fundamentos y procesos químicos con fluidos supercríticos
(2019) Calvo Garrido, Lourdes; Cabañas Poveda, Albertina; Pando García-Pumarino, Concepción; García Baonza, Valentín; González Mac-Dowell, Luis; Tirado Armesto, Diego Felipe; Cuadra Mendoza, Isaac Alfonso; Menéndez Carbajosa, Alicia Marta; Calvo Garrido, María Lourdes
El objetivo del proyecto ha sido crear un laboratorio integrado de prácticas de simulación relacionadas con fundamentos termodinámicos y procesos con fluidos supercríticos, destinado a los alumnos de Química e Ingeniería Química.