La dinámica molecular es una herramienta muy útil para estudiar los fenómenos interfaciales. Aquí... more La dinámica molecular es una herramienta muy útil para estudiar los fenómenos interfaciales. Aquí se presenta un procedimiento usando el programa GROMACS-4.5.4, el cual es empleado en el laboratorio de fisicoquímica, para estimar la tensión interfacial y el espesor de película interfacial del sistema agua/n-octano con el modelo de Kirkwood-Buff y la teoría onda-capilar. En la simulación, se utilizan los tensores de presión y la tensión interfacial más aceptable fue obtenida combinando los modelos TIP3P y GROMOS53A6 para el agua y n-octano.
La dinámica molecular es una herramienta muy útil para estudiar los fenómenos interfaciales. Aquí... more La dinámica molecular es una herramienta muy útil para estudiar los fenómenos interfaciales. Aquí se presenta un procedimiento usando el programa GROMACS-4.5.4, el cual es empleado en el laboratorio de fisicoquímica, para estimar la tensión interfacial y el espesor de película interfacial del sistema agua/n-octano con el modelo de Kirkwood-Buff y la teoría onda-capilar. En la simulación, se utilizan los tensores de presión y la tensión interfacial más aceptable fue obtenida combinando los modelos TIP3P y GROMOS53A6 para el agua y n-octano.
La dinámica molecular es una herramienta muy útil para estudiar los fenómenos interfaciales. Aquí... more La dinámica molecular es una herramienta muy útil para estudiar los fenómenos interfaciales. Aquí se presenta un procedimiento usando el programa GROMACS-4.5.4, el cual es empleado en el laboratorio de fisicoquímica, para estimar la tensión interfacial y el espesor de película interfacial del sistema agua/n-octano con el modelo de Kirkwood-Buff y la teoría onda-capilar. En la simulación, se utilizan los tensores de presión y la tensión interfacial más aceptable fue obtenida combinando los modelos TIP3P y GROMOS53A6 para el agua y n-octano.
This paper describes experimental results of thermal diffusivity measurements performed on differ... more This paper describes experimental results of thermal diffusivity measurements performed on different concentrations of aqueous Tartrazine solutions. The measurements are performed using the frequency-resolved thermal lensing technique and the results are compared with the thermal diffusivity value of pure water used as a solvent or host liquid. The results show that at low concentrations, the thermal properties of the solution are roughly equal to those of the water. However, when the concentration is increased, the thermal properties of the solutions diverge from that of the host liquid.
In this work, we report a joint experimental-theoretical investigation on interaction of vacuum-u... more In this work, we report a joint experimental-theoretical investigation on interaction of vacuum-ultraviolet radiation with trimethylphosphate (TMP) molecule (C(3)H(9)O(4)P) in gas phase. This species together with tetrahydrofuran (THF) are model compounds of deoxyribose nucleic acids (DNA)/ribose nucleic acids (RNA) backbone. Absolute photoabsorption cross sections (σ(a)) and ionization yields (η) are measured using the double-ion-chamber technique in the 11.0-21.45 eV energy range. Photoionization (σ(i)) and neutral-decay (σ(n)) cross sections in absolute scale are also derived. Moreover, theoretical photoabsorption cross sections are calculated using the time-dependent density functional theory from the excitation threshold up to 16 eV. Good agreement between the present calculated and experimental photoabsorption cross sections in the 11.0-14.5 eV range is encouraging. Also, the present measured data of σ(a) and σ(i) for TMP are about 1.3 and 1.5 times of those of THF, respective...
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2006
The initial velocity distribution of secondary ions is employed as a tool to analyze nuclear trac... more The initial velocity distribution of secondary ions is employed as a tool to analyze nuclear track formation processes occurring in the picosecond time range. The choice of the secondary ion for such analysis depends on the particular surface region and on the desorption time range of interest: (a) H + ions are emitted promptly from the impact site, (b) H À desorption occurs delayed and mostly from the impact periphery, (c) emitted molecular ions are accelerated away during tens of picoseconds exclusively from the impact periphery. The model is set up considering the track as two coaxial cylinders, the inner one positively charged and the outer one negatively charged. It takes into account effects due to the track charge image formed by a metallic substrate, the projectile angle of incidence, the variation of the electronic stopping power for projectiles out of the equilibrium-charge regime, and a positive and negative track neutralization whose rates are exponentially decreasing with time. Predictions of the model are presented for ion desorption of LiF bombarded by 1 MeV Ar ions.
Journal of Physics B: Atomic, Molecular and Optical Physics, 2009
... where R is the gas constant and T is the temperature in kelvin. The measurements were perform... more ... where R is the gas constant and T is the temperature in kelvin. The measurements were performed several times in order to check the reproducibility of the results. ... Soc. Am. B 6 2326 [16] Samson JAR and Stolte WC 2002 J. Electron Spectrosc. Relat. Phenom. ...
Two ices, O2 and a mixture of O2 and N2, are bombarded by 252Cf fission fragments (FF) (approxima... more Two ices, O2 and a mixture of O2 and N2, are bombarded by 252Cf fission fragments (FF) (approximately 65 MeV at target surface); the emitted positive and negative secondary ions are analyzed by time-of-flight mass spectrometry (TOF-SIMS). These studies shall enlighten sputtering from planetary and interstellar ices. Three temperature regions in the 28-42-K range are analyzed: (1) before N2 sublimation, in which hybrid chemical species are formed, (2) before O2 sublimation, in which the TOF mass spectrum is dominated by low-mass (O2)p cluster ions and (3) after O2 sublimation, in which (N2)p or (O2)p cluster ions are practically inexistent. In the first region, four hybrid ion series are observed: NOn-1+, N2On-2(+/-), and N4On-4(-). In the second region, two positive and negative ion series are identified: (O2)pO(+/-) and (O2)pO2(+/-). Their yield distributions are fitted by the sum of two decreasing exponentials, whose decay constants are the same for all series. It is observed that the cluster ion desorption from solid oxygen is very similar to that of other frozen gases, but its yield distribution oscillates with a three- or six-atom periodicity, suggesting O3 or 3O2 units in the cluster structure, respectively.
CO-NH(3) and CO-NH(3)-H(2)O ices at 25-130 K were bombarded by (252)Cf fission fragments ( approx... more CO-NH(3) and CO-NH(3)-H(2)O ices at 25-130 K were bombarded by (252)Cf fission fragments ( approximately 65 MeV at the target surface) and the emitted secondary ions were analyzed by time-of-flight mass spectrometry (TOF-SIMS). It is observed that the mass spectra obtained from both ices have similar patterns. The production of hybrid ions (formed from CO and NH(3) molecules) emitted from CO-NH(3) ice has already been reported by R. Martinez et al., Int. J. Mass. Spectrom. 262 (2006) 195; here, the secondary ion emission and the modifications of the CO--NH(3) ice structure during the temperature increase of the ice are addressed. These studies are expected to throw light on the sputtering from planetary and interstellar ices and the possible formation of new organic molecules in CO-NH(3)-H(2)O ice by megaelectronvolt ion bombardment. The presence of water in the CO-NH(3) ice mixture generates molecular ion series such as (NH(3))(p-q)(H(2)O)(q)CO(+) and replaces the cluster series (NH(3))(n)NH(4) (+) emission by the hybrid series (NH(3))(I-i)(H(2)O)(i=1, 2...I)H(+). The distribution of NH(3) and H(2)O molecules within the cluster groups indicates that ammonia and water mix homogeneously in the icy condensate at T = 25 K. The desorption yield distribution of the cluster series (NH(3))(n)NH(4) (+) is described by the sum of two exponential functions: one, slow-decreasing, attributed to the fragmentation of the solid target into clusters; and another, fast-decreasing, due to a local sublimation followed by recombination of ammonia molecules. The analysis of the time-temperature dependence of these two yield components gives information on the formation process of molecular ions, the transient composition of the ice target and structural changes of the ice. Data suggest that the amorphous and porous structure of the NH(3) ice, formed by the condensation of the CO--NH(3) gas at T = 25 K, survives CO sublimation until the occurrence of a phase transition around 80 K, which produces a more fragile ice structure.
Journal of Electron Spectroscopy and Related Phenomena, 2007
Planetary magnetospheres, in which outer planet satellites orbit, are bombarded by energetic part... more Planetary magnetospheres, in which outer planet satellites orbit, are bombarded by energetic particles inducing chemical and physical changes in their icy surfaces. The existing condensed gases react to form new products, which then undergo thermal evolution from the natural day/night cycles of these satellites. Plasma irradiation of ice causes phase changes, e.g., water ice from crystalline to amorphous over short
Ion cluster desorption yields due to the impact of 252Cf fission fragments on condensed ammonia a... more Ion cluster desorption yields due to the impact of 252Cf fission fragments on condensed ammonia are determined. Identification and abundance of the ion desorbed species were provided by a time-of-flight mass spectrometer. Ammonia ice thin layers deposited on Au film were heated from 25K to complete sublimation. The typical pressure during heating process was 10−8mbar. Measurements in the 25–150K temperature
Frozen CO was bombarded by ∼65MeV fission fragments and the emitted secondary ions were analyzed ... more Frozen CO was bombarded by ∼65MeV fission fragments and the emitted secondary ions were analyzed by time-of-flight mass spectrometry. Target was kept at UHV conditions and its temperature was varied from 25K up to complete sublimation of the ice film. The observed positive cluster ion series are well represented by the chemical expression (CO)mCn+, where m and n≥0, and the
La dinámica molecular es una herramienta muy útil para estudiar los fenómenos interfaciales. Aquí... more La dinámica molecular es una herramienta muy útil para estudiar los fenómenos interfaciales. Aquí se presenta un procedimiento usando el programa GROMACS-4.5.4, el cual es empleado en el laboratorio de fisicoquímica, para estimar la tensión interfacial y el espesor de película interfacial del sistema agua/n-octano con el modelo de Kirkwood-Buff y la teoría onda-capilar. En la simulación, se utilizan los tensores de presión y la tensión interfacial más aceptable fue obtenida combinando los modelos TIP3P y GROMOS53A6 para el agua y n-octano.
La dinámica molecular es una herramienta muy útil para estudiar los fenómenos interfaciales. Aquí... more La dinámica molecular es una herramienta muy útil para estudiar los fenómenos interfaciales. Aquí se presenta un procedimiento usando el programa GROMACS-4.5.4, el cual es empleado en el laboratorio de fisicoquímica, para estimar la tensión interfacial y el espesor de película interfacial del sistema agua/n-octano con el modelo de Kirkwood-Buff y la teoría onda-capilar. En la simulación, se utilizan los tensores de presión y la tensión interfacial más aceptable fue obtenida combinando los modelos TIP3P y GROMOS53A6 para el agua y n-octano.
La dinámica molecular es una herramienta muy útil para estudiar los fenómenos interfaciales. Aquí... more La dinámica molecular es una herramienta muy útil para estudiar los fenómenos interfaciales. Aquí se presenta un procedimiento usando el programa GROMACS-4.5.4, el cual es empleado en el laboratorio de fisicoquímica, para estimar la tensión interfacial y el espesor de película interfacial del sistema agua/n-octano con el modelo de Kirkwood-Buff y la teoría onda-capilar. En la simulación, se utilizan los tensores de presión y la tensión interfacial más aceptable fue obtenida combinando los modelos TIP3P y GROMOS53A6 para el agua y n-octano.
This paper describes experimental results of thermal diffusivity measurements performed on differ... more This paper describes experimental results of thermal diffusivity measurements performed on different concentrations of aqueous Tartrazine solutions. The measurements are performed using the frequency-resolved thermal lensing technique and the results are compared with the thermal diffusivity value of pure water used as a solvent or host liquid. The results show that at low concentrations, the thermal properties of the solution are roughly equal to those of the water. However, when the concentration is increased, the thermal properties of the solutions diverge from that of the host liquid.
In this work, we report a joint experimental-theoretical investigation on interaction of vacuum-u... more In this work, we report a joint experimental-theoretical investigation on interaction of vacuum-ultraviolet radiation with trimethylphosphate (TMP) molecule (C(3)H(9)O(4)P) in gas phase. This species together with tetrahydrofuran (THF) are model compounds of deoxyribose nucleic acids (DNA)/ribose nucleic acids (RNA) backbone. Absolute photoabsorption cross sections (σ(a)) and ionization yields (η) are measured using the double-ion-chamber technique in the 11.0-21.45 eV energy range. Photoionization (σ(i)) and neutral-decay (σ(n)) cross sections in absolute scale are also derived. Moreover, theoretical photoabsorption cross sections are calculated using the time-dependent density functional theory from the excitation threshold up to 16 eV. Good agreement between the present calculated and experimental photoabsorption cross sections in the 11.0-14.5 eV range is encouraging. Also, the present measured data of σ(a) and σ(i) for TMP are about 1.3 and 1.5 times of those of THF, respective...
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2006
The initial velocity distribution of secondary ions is employed as a tool to analyze nuclear trac... more The initial velocity distribution of secondary ions is employed as a tool to analyze nuclear track formation processes occurring in the picosecond time range. The choice of the secondary ion for such analysis depends on the particular surface region and on the desorption time range of interest: (a) H + ions are emitted promptly from the impact site, (b) H À desorption occurs delayed and mostly from the impact periphery, (c) emitted molecular ions are accelerated away during tens of picoseconds exclusively from the impact periphery. The model is set up considering the track as two coaxial cylinders, the inner one positively charged and the outer one negatively charged. It takes into account effects due to the track charge image formed by a metallic substrate, the projectile angle of incidence, the variation of the electronic stopping power for projectiles out of the equilibrium-charge regime, and a positive and negative track neutralization whose rates are exponentially decreasing with time. Predictions of the model are presented for ion desorption of LiF bombarded by 1 MeV Ar ions.
Journal of Physics B: Atomic, Molecular and Optical Physics, 2009
... where R is the gas constant and T is the temperature in kelvin. The measurements were perform... more ... where R is the gas constant and T is the temperature in kelvin. The measurements were performed several times in order to check the reproducibility of the results. ... Soc. Am. B 6 2326 [16] Samson JAR and Stolte WC 2002 J. Electron Spectrosc. Relat. Phenom. ...
Two ices, O2 and a mixture of O2 and N2, are bombarded by 252Cf fission fragments (FF) (approxima... more Two ices, O2 and a mixture of O2 and N2, are bombarded by 252Cf fission fragments (FF) (approximately 65 MeV at target surface); the emitted positive and negative secondary ions are analyzed by time-of-flight mass spectrometry (TOF-SIMS). These studies shall enlighten sputtering from planetary and interstellar ices. Three temperature regions in the 28-42-K range are analyzed: (1) before N2 sublimation, in which hybrid chemical species are formed, (2) before O2 sublimation, in which the TOF mass spectrum is dominated by low-mass (O2)p cluster ions and (3) after O2 sublimation, in which (N2)p or (O2)p cluster ions are practically inexistent. In the first region, four hybrid ion series are observed: NOn-1+, N2On-2(+/-), and N4On-4(-). In the second region, two positive and negative ion series are identified: (O2)pO(+/-) and (O2)pO2(+/-). Their yield distributions are fitted by the sum of two decreasing exponentials, whose decay constants are the same for all series. It is observed that the cluster ion desorption from solid oxygen is very similar to that of other frozen gases, but its yield distribution oscillates with a three- or six-atom periodicity, suggesting O3 or 3O2 units in the cluster structure, respectively.
CO-NH(3) and CO-NH(3)-H(2)O ices at 25-130 K were bombarded by (252)Cf fission fragments ( approx... more CO-NH(3) and CO-NH(3)-H(2)O ices at 25-130 K were bombarded by (252)Cf fission fragments ( approximately 65 MeV at the target surface) and the emitted secondary ions were analyzed by time-of-flight mass spectrometry (TOF-SIMS). It is observed that the mass spectra obtained from both ices have similar patterns. The production of hybrid ions (formed from CO and NH(3) molecules) emitted from CO-NH(3) ice has already been reported by R. Martinez et al., Int. J. Mass. Spectrom. 262 (2006) 195; here, the secondary ion emission and the modifications of the CO--NH(3) ice structure during the temperature increase of the ice are addressed. These studies are expected to throw light on the sputtering from planetary and interstellar ices and the possible formation of new organic molecules in CO-NH(3)-H(2)O ice by megaelectronvolt ion bombardment. The presence of water in the CO-NH(3) ice mixture generates molecular ion series such as (NH(3))(p-q)(H(2)O)(q)CO(+) and replaces the cluster series (NH(3))(n)NH(4) (+) emission by the hybrid series (NH(3))(I-i)(H(2)O)(i=1, 2...I)H(+). The distribution of NH(3) and H(2)O molecules within the cluster groups indicates that ammonia and water mix homogeneously in the icy condensate at T = 25 K. The desorption yield distribution of the cluster series (NH(3))(n)NH(4) (+) is described by the sum of two exponential functions: one, slow-decreasing, attributed to the fragmentation of the solid target into clusters; and another, fast-decreasing, due to a local sublimation followed by recombination of ammonia molecules. The analysis of the time-temperature dependence of these two yield components gives information on the formation process of molecular ions, the transient composition of the ice target and structural changes of the ice. Data suggest that the amorphous and porous structure of the NH(3) ice, formed by the condensation of the CO--NH(3) gas at T = 25 K, survives CO sublimation until the occurrence of a phase transition around 80 K, which produces a more fragile ice structure.
Journal of Electron Spectroscopy and Related Phenomena, 2007
Planetary magnetospheres, in which outer planet satellites orbit, are bombarded by energetic part... more Planetary magnetospheres, in which outer planet satellites orbit, are bombarded by energetic particles inducing chemical and physical changes in their icy surfaces. The existing condensed gases react to form new products, which then undergo thermal evolution from the natural day/night cycles of these satellites. Plasma irradiation of ice causes phase changes, e.g., water ice from crystalline to amorphous over short
Ion cluster desorption yields due to the impact of 252Cf fission fragments on condensed ammonia a... more Ion cluster desorption yields due to the impact of 252Cf fission fragments on condensed ammonia are determined. Identification and abundance of the ion desorbed species were provided by a time-of-flight mass spectrometer. Ammonia ice thin layers deposited on Au film were heated from 25K to complete sublimation. The typical pressure during heating process was 10−8mbar. Measurements in the 25–150K temperature
Frozen CO was bombarded by ∼65MeV fission fragments and the emitted secondary ions were analyzed ... more Frozen CO was bombarded by ∼65MeV fission fragments and the emitted secondary ions were analyzed by time-of-flight mass spectrometry. Target was kept at UHV conditions and its temperature was varied from 25K up to complete sublimation of the ice film. The observed positive cluster ion series are well represented by the chemical expression (CO)mCn+, where m and n≥0, and the
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