FERNANDO VELAZQUEZ AGUIRRE - Academia.edu (original) (raw)
Papers by FERNANDO VELAZQUEZ AGUIRRE
Estudios Gerenciales, 2012
El objetivo del artículo es proponer un modelo de análisis multinivel de la innovación. Se expone... more El objetivo del artículo es proponer un modelo de análisis multinivel de la innovación. Se exponen los debates acerca de los efectos del ambiente regional sobre el desempeño innovador de las firmas y se sostiene que la innovación se debe comprender desde una óptica multinivel que incluyan las características del ambiente regional así como las capacidades de la firma. Para lograr este objetivo, se construyó un modelo estadístico multinivel, el cual arrojó evidencia sobre los beneficios de este enfoque en la innovación empresarial. Los resultados sugieren el enfoque multinivel para futuras investigación sobre innovación.
Revista Pueblos y fronteras digital, 2011
Se comparte una lectura crítica de las representaciones sociales que los chuj mexicanos construye... more Se comparte una lectura crítica de las representaciones sociales que los chuj mexicanos construyen en torno a la educación escolar básica, la cual tiene como núcleo central el aprender a leer y escribir, así como hablar en español. Este texto pretende ser un aporte con doble direccionalidad, por un lado para los interesados en el tema de la educación escolar básica y dentro de ellos los interesados en temas de educación intercultural o de educación indígena; y, por el otro, para quienes están preocupados por conocer el alcance de las representaciones sociales, resaltando su valor crítico. ABSTRACTThis paper presents a critical reading of the social representations the Chuj people in Mexico construct around basic schooling, the core component of which is the teaching of reading and writing, as well as of speaking Spanish. This text aims to be a contribution to those interested in basic schooling, specifically those interested in intercultural education or indigenous education, as w...
Spie Proceedings Series, 2002
The recent observation that n-type conductivity in ZnO is due to hydrogen doping open the avenue ... more The recent observation that n-type conductivity in ZnO is due to hydrogen doping open the avenue for p-doping to form p-n junction devices in ZnO. The possibility of the solid solutions with MgO provides the opportunity in ZnO/ZnMgO quantum well structures. We present the synthesis and structural properties of Zn (Mg,Li)O with possible opportunity of p-doping in this material system.
[1990] Proceedings. 10th International Conference on Pattern Recognition
... Ther&e, the linarhtim threshold po that keeps Q% of the pointsinthefunctionH(p)isgknby: L... more ... Ther&e, the linarhtim threshold po that keeps Q% of the pointsinthefunctionH(p)isgknby: L= C{H(P); P = 0, NGI (1) ... 58 E@, p. 9f3!xK [4 DH Ballard, " G enerw the Hough transform to detect arhtraryshapes," Pattern Recognition, Vol. 13, No. ...
Estudios Gerenciales, Sep 1, 2013
Estudios Gerenciales, 2013
El objetivo del presente artículo es determinar los efectos que ejerce la apuesta estratégica de ... more El objetivo del presente artículo es determinar los efectos que ejerce la apuesta estratégica de innovación de las empresas manufactureras colombianas sobre la decisión de proteger sus innovaciones con registro de propiedad intelectual (patentes). Para lo anterior, se utilizó un Zero Inflated Poisson Model sobre datos provenientes de la 2.ª y 3.ª Encuesta de Desarrollo e Innovación Tecnológica efectuada por DANE-DNP-COLCIENCIAS. Los resultados de esta investigación evidencian una relación negativa entre la proporción de inversión en inversión y desarrollo y la decisión de patentar. Adicionalmente, el bajo nivel de patentes se debe en parte a la carencia de relaciones de calidad de las firmas con proveedores y competencia.
The Journal of Physical Chemistry A, 2000
Photodissociation of thermalized NiOH + and NiOH + (H 2 O) are examined over the visible and near... more Photodissociation of thermalized NiOH + and NiOH + (H 2 O) are examined over the visible and near-ultraviolet using time-of-flight mass spectrometry. Branching ratios and photodissociation cross sections are monitored as a function of laser wavelength. Loss of OH is the only dissociation channel observed in NiOH + , whereas loss of H 2 O and OH are present, and competitive, in the photodissociation of NiOH + (H 2 O). The photofragment spectrum of NiOH + shows absorption bands at ∼300 and ∼400 nm. An almost identical spectrum is observed for the net photodissociation of NiOH + (H 2 O). Spectroscopic thresholds taken from the photofragment spectra have been corrected to yield upper limits to the 0 K bond energies for the ions: D o 0 (Ni +-OH) e 271 (9 kJ/mol, D o 0 (NiOH +-H 2 O) e 271 (9 kJ/mol, and D o 0 (Ni + H 2 O-OH) e 334 (5 kJ/mol. Calculated B3LYP values are consistent with the experimental upper limits, but suggest that the true D o 0 (NiOH +-H 2 O) and D o 0 (Ni + H 2 O-OH) lie significantly below these upper limits. Photodissociation of NiOH + (H 2 O) near 300 nm leads to greater OH production than RRKM calculations predict, suggesting that excitation in this region leads to direct Ni +-OH bond cleavage.
The Journal of Physical Chemistry A, 2006
The photodissociation of propargyl chloride (C 3 H 3 Cl) has been studied at 193 nm. Ion imaging ... more The photodissociation of propargyl chloride (C 3 H 3 Cl) has been studied at 193 nm. Ion imaging experiments with state-selective detection of the Cl atoms and single-photon ionization of the C 3 H 3 radicals were performed, along with measurements of the Cl + C 3 H 3 and HCl + C 3 H 2 recoil kinetic energy distributions, using a scattering apparatus with electron bombardment ionization detection to resolve the competing Cl and HCl elimination channels. The experiments allow the determination of the Cl (2 P 3/2) and Cl (2 P 1/2) (hereafter Cl*) branching fractions associated with the C-Cl bond fission, which are determined to be 0.5 (0.1 for both channels. Although prior translational spectroscopy studies by others had concluded that the low velocity signal at the Cl + mass was due to daughter fragments of the HCl elimination products, the present work shows that Cl atoms are produced with a bimodal recoil kinetic energy distribution. The major C-Cl bond fission channel, with a narrow recoil kinetic energy distribution peaking near 40 kcal/mol, produces both Cl and Cl*, whereas the minor (5%) channel, partitioning much less energy to relative kinetic energy, produces only ground spin-orbit state Cl atoms. The maximum internal energy of the radicals produced in the lowrecoil-kinetic-energy channel is consistent with this channel producing electronically excited propargyl radicals. Finally, in contrast to previous studies, the present work determines the HCl recoil kinetic energy distribution and identifies the possible contribution to this spectrum from propargyl radicals cracking to C 3 + ions in the mass spectrometer.
The Journal of Physical Chemistry A, 2004
Two-color, two-photon resonant, three-photon ionization, and high-resolution photoelectron spectr... more Two-color, two-photon resonant, three-photon ionization, and high-resolution photoelectron spectroscopy are combined to characterize the photoionization dynamics of the 3pσ 2 Σ u + electronic state of NO 2. Direct photoionization of selected vibrational levels of the NO 2 3pσ 2 Σ u + state shows a strong propensity to preserve the vibrational quantum numbers of the intermediate state. Efficient methods for producing NO 2 + X 1 Σ u + (000), (010), (100), and (001) with over 95% purity are discussed. This approach is expected to be applicable to the study of the mode dependence of the effects of vibrational excitation in ion-molecule reactions involving NO 2 + .
The Journal of Physical Chemistry A, 2000
Photofragment spectra of jet-cooled MCH 2 + (M) Fe, Co, Ni) have been measured. Our investigation... more Photofragment spectra of jet-cooled MCH 2 + (M) Fe, Co, Ni) have been measured. Our investigation of NiCH 2 + represents the first reported spectroscopic study of this molecule. A spectroscopic threshold is observed for each of the three systems. In addition to imposing strict upper limits on the M +-CH 2 bond strengths, these results further the discussion concerning the interpretation of spectroscopic thresholds as thermodynamic limits. The measured upper limits are: D°0(Fe +-CH 2) e 342 (2 kJ/mol, D°0(Co +-CH 2) e 331 (2 kJ/ mol, and D°0(Ni +-CH 2) e 295 (5 kJ/mol. Three distinct, 2-nm-wide peaks are observed in the photofragment spectrum of CoCH 2 + , but the spectra lack sharp structure above threshold.
The Journal of Physical Chemistry A, 2000
Hydrated divalent nickel clusters, Ni 2+ (H 2 O) n (n) 4-7), have been generated through electros... more Hydrated divalent nickel clusters, Ni 2+ (H 2 O) n (n) 4-7), have been generated through electrospray ionization and studied with laser photofragment spectroscopy. Clusters containing six and seven water molecules dissociate by loss of either one or two water molecules. In contrast, Ni 2+ (H 2 O) 4 dissociates via charge reduction, producing H 3 O + + NiOH + (H 2 O) 2. The modest kinetic energy release in the H 3 O + product is in agreement with a saltbridge dissociation mechanism. Observed dissociation cross-sections indicate that the hexahydrated species is the probable carrier for nickel's aqueous absorption spectrum.
SIMULATION, 1990
This paper discusses an efficient method for handling time dependent boundary conditions with the... more This paper discusses an efficient method for handling time dependent boundary conditions with the DSS/2 differential equation solver. The method was evaluated by using it in the numerical solution of a diffusion problem. The proposed method is also particularly useful for boundary conditions in which only derivatives of the depend ent variables are involved. The method is based on transforming the boundary conditions at the interface to a set of algebraic equations which must be solved simultaneously at each integra tion step. Both algebraic and numerical solutions of this set of equations are discussed, and the relative merits of each one of these solutions are evaluated. The proposed method provides significant improvements in computation times and is capable of handling more complex boundary conditions as compared to other conventional methods.
Phys. Chem. Chem. Phys., 2005
Solvated cluster ions Co 21 (CH 3 OH) n (n ¼ 4-7) have been produced by electrospray and studied ... more Solvated cluster ions Co 21 (CH 3 OH) n (n ¼ 4-7) have been produced by electrospray and studied using photofragment spectroscopy. There are notable differences between the photodissociation spectra of these complexes and the analogous water complexes. Co 21 (CH 3 OH) 6 absorbs significantly more strongly than Co 21 (H 2 O) 6. The photodissociation spectra of Co 21 (CH 3 OH) n (n ¼ 4, 5 and 6) are very similar, which suggests that they share the Co 21 (CH 3 OH) 4 chromophore, with additional solvent molecules in the second shell. In contrast, our earlier studies indicate that Co 21 (H 2 O) 6 is six coordinate, and its spectrum is significantly different from that of Co 21 (H 2 O) 4. The larger clusters Co 21 (CH 3 OH) n (n ¼ 5-7) dissociate by simple loss of one or more solvent molecules. Larger clusters tend to lose more solvent molecules, especially at higher photon energies. As with the corresponding water cluster, Co 21 (CH 3 OH) 4 photodissociates by proton transfer through a salt-bridge intermediate. This is accompanied by a modest kinetic energy release of 170 kJ mol À1 and occurs with a lifetime of 145 ns.
Journal of Elastomers & Plastics, 2013
Histogram analyses of atomic force microscopy (AFM) phase images demonstrated changes in the surf... more Histogram analyses of atomic force microscopy (AFM) phase images demonstrated changes in the surface composition of ethylene propylene diene–modified (EPDM) elastomeric formulations containing polybutadiene after exposure to hydrazine. It was determined by Fourier-transform infrared (FT-IR) spectroscopic analysis that the change in the surface composition is caused by hydrogenation of the vinylic double bonds of the polybutadiene coagent, stemming from diimide generation from hydrazine. The diffusion and subsequent reaction of hydrazine with two cured EPDM elastomeric formulations were investigated by mapping FT-IR spectroscopy. The depth of diffusion and reaction was determined by monitoring changes in the intensity of the vinyl group signal from the polybutadiene in the FT-IR spectra. The FT-IR analysis of horizontal microtome specimens and vertical ‘cross section’ of the EPDM samples showed that hydrazine diffused less than 200 μm into the elastomeric materials over a period of 4...
The Journal of Chemical Physics, 1999
We report the first vibrationally resolved spectroscopic study of FeO ϩ. We observe the 0←0 and 1... more We report the first vibrationally resolved spectroscopic study of FeO ϩ. We observe the 0←0 and 1←0 bands of a 6 ⌺←X 6 ⌺ transition at 28 648.7 and 29 311 cm Ϫ1. Under slightly modified source conditions the 1←1 transition is observed at 28 473 cm Ϫ1. In addition to establishing an upper limit D 0 o (Fe ϩ-O͒р342.7 kJ/mol, our results give the first experimental measurements of the vibrational frequencies in both the ground state, 0 Љϭ838Ϯ4 cm Ϫ1 , and the excited electronic state, 0 Јϭ662 Ϯ2 cm Ϫ1. Partially resolved rotational structure underlying the vibrational peaks has been analyzed to measure the predissociation lifetime and estimate the change in molecular constants upon electronic excitation.
The Journal of Chemical Physics, 2004
The photoionization and photodissociation dynamics of H(2) and D(2) in selected rovibrational lev... more The photoionization and photodissociation dynamics of H(2) and D(2) in selected rovibrational levels of the B (1)Sigma(u) (+) and C (1)Pi(u) states have been investigated by velocity map ion imaging. The selected rotational levels of the B (1)Sigma(u) (+) and C (1)Pi(u) states are prepared by three-photon excitation from the ground state. The absorption of fourth photon results in photoionization to produce H(2)(+) X (2)Sigma(g)(+) or photodissociation to produce a ground-state H(1s) atom and an excited H atom with n >or= 2. The H(2) (+) ion can be photodissociated by absorption of a fifth photon. The resulting H(+) or D(+) ion images provide information on the vibrational state dependence of the photodissociation angular distribution of the molecular ion. The excited H(n >or= 2) atoms produced by the neutral dissociation process can also be ionized by the absorption of a fifth photon. The resulting ion images provide insight into the excited state branching ratios and angular distributions of the neutral photodissociation process. While the experimental ion images contain information on both the ionic and neutral processes, these can be separated based on constraints imposed on the fragment translational energies. The angular distribution of the rings in the ion images indicates that the neutral dissociation of molecular hydrogen and its isotopes is quite complex, and involves coupling to both doubly excited electronic states and the dissociation continua of singly excited Rydberg states.
The Journal of Chemical Physics, 2002
Specific ion-molecule reactions are used to prepare two intermediates of the FeO ϩ ϩCH 4 reaction... more Specific ion-molecule reactions are used to prepare two intermediates of the FeO ϩ ϩCH 4 reaction, and photodissociation of the jet-cooled intermediates is examined in the visible and near-ultraviolet using time-of-flight mass spectrometry. The photodissociation spectrum of the aquo iron carbene complex ͓H 2 CvFe-OH 2 ͔ ϩ shows transitions to at least four excited electronic states in the FeCH 2 ϩ chromophore, with broad vibrational structure. Photoexcitation of the insertion intermediate ͓HO-Fe-CH 3 ͔ ϩ leads to formation of FeOH ϩ ϩCH 3 and also triggers the reaction to produce Fe ϩ ϩCH 3 OH. The photodissociation spectrum of ͓HO-Fe-CH 3 ͔ ϩ presents a vibrationally resolved band involving progressions in the excited state Fe-C stretch, Fe-O stretch, and O-Fe-C bend. The change in the Fe-C bond length in ͓HO-Fe-CH 3 ͔ ϩ and ͓H 2 CvFe-OH 2 ͔ ϩ upon photoexcitation is calculated from a Franck-Condon analysis of the vibronic features observed. The analysis of the experimental results is aided by hybrid Hartree-Fock/density-functional ͑B3LYP͒ calculations on ͓HO-Fe-CH 3 ͔ ϩ and ͓H 2 CvFe-OH 2 ͔ ϩ performed to determine molecular parameters, and time-dependent density functional theory ͑TD-DFT͒ calculations on FeCH 2 ϩ to predict excited electronic states.
The Journal of Chemical Physics, 2003
The resonance enhanced ͑1ϩ1͒ photodissociation spectra of the ͑8,0͒ and ͑9,0͒ bands of the 6 ⌸ 7/... more The resonance enhanced ͑1ϩ1͒ photodissociation spectra of the ͑8,0͒ and ͑9,0͒ bands of the 6 ⌸ 7/2 ← 6 ⌺ ϩ system of FeO ϩ have been recorded. From a rotational analysis, the rotational parameters for the 6 ⌺ ϩ ground state of FeO ϩ have been obtained for the first time. The rotational constant B 0 ϭ0.5020Ϯ0.0004 cm Ϫ1 is derived, giving r 0 ϭ1.643Ϯ0.001 Å. Other molecular parameters determined for the 6 ⌺ ϩ ground state are the spin-spin coupling constant, ϭϪ0.126Ϯ0.006 cm Ϫ1 , and the spin-rotational coupling constant, ␥ϭϪ0.033Ϯ0.002 cm Ϫ1. The assignment of the upper state as 6 ⌸ 7/2 is based on the characteristic appearance of the band and on time-dependent density functional ͑TD-DFT͒ calculations performed on FeO ϩ. The reliability of the TD-DFT method in the prediction of excited states of FeO ϩ is corroborated by calculations on CrF and MnO, which have been extensively characterized either by spectroscopy or by high-level theoretical calculations.
Estudios Gerenciales, 2012
El objetivo del artículo es proponer un modelo de análisis multinivel de la innovación. Se expone... more El objetivo del artículo es proponer un modelo de análisis multinivel de la innovación. Se exponen los debates acerca de los efectos del ambiente regional sobre el desempeño innovador de las firmas y se sostiene que la innovación se debe comprender desde una óptica multinivel que incluyan las características del ambiente regional así como las capacidades de la firma. Para lograr este objetivo, se construyó un modelo estadístico multinivel, el cual arrojó evidencia sobre los beneficios de este enfoque en la innovación empresarial. Los resultados sugieren el enfoque multinivel para futuras investigación sobre innovación.
Revista Pueblos y fronteras digital, 2011
Se comparte una lectura crítica de las representaciones sociales que los chuj mexicanos construye... more Se comparte una lectura crítica de las representaciones sociales que los chuj mexicanos construyen en torno a la educación escolar básica, la cual tiene como núcleo central el aprender a leer y escribir, así como hablar en español. Este texto pretende ser un aporte con doble direccionalidad, por un lado para los interesados en el tema de la educación escolar básica y dentro de ellos los interesados en temas de educación intercultural o de educación indígena; y, por el otro, para quienes están preocupados por conocer el alcance de las representaciones sociales, resaltando su valor crítico. ABSTRACTThis paper presents a critical reading of the social representations the Chuj people in Mexico construct around basic schooling, the core component of which is the teaching of reading and writing, as well as of speaking Spanish. This text aims to be a contribution to those interested in basic schooling, specifically those interested in intercultural education or indigenous education, as w...
Spie Proceedings Series, 2002
The recent observation that n-type conductivity in ZnO is due to hydrogen doping open the avenue ... more The recent observation that n-type conductivity in ZnO is due to hydrogen doping open the avenue for p-doping to form p-n junction devices in ZnO. The possibility of the solid solutions with MgO provides the opportunity in ZnO/ZnMgO quantum well structures. We present the synthesis and structural properties of Zn (Mg,Li)O with possible opportunity of p-doping in this material system.
[1990] Proceedings. 10th International Conference on Pattern Recognition
... Ther&e, the linarhtim threshold po that keeps Q% of the pointsinthefunctionH(p)isgknby: L... more ... Ther&e, the linarhtim threshold po that keeps Q% of the pointsinthefunctionH(p)isgknby: L= C{H(P); P = 0, NGI (1) ... 58 E@, p. 9f3!xK [4 DH Ballard, " G enerw the Hough transform to detect arhtraryshapes," Pattern Recognition, Vol. 13, No. ...
Estudios Gerenciales, Sep 1, 2013
Estudios Gerenciales, 2013
El objetivo del presente artículo es determinar los efectos que ejerce la apuesta estratégica de ... more El objetivo del presente artículo es determinar los efectos que ejerce la apuesta estratégica de innovación de las empresas manufactureras colombianas sobre la decisión de proteger sus innovaciones con registro de propiedad intelectual (patentes). Para lo anterior, se utilizó un Zero Inflated Poisson Model sobre datos provenientes de la 2.ª y 3.ª Encuesta de Desarrollo e Innovación Tecnológica efectuada por DANE-DNP-COLCIENCIAS. Los resultados de esta investigación evidencian una relación negativa entre la proporción de inversión en inversión y desarrollo y la decisión de patentar. Adicionalmente, el bajo nivel de patentes se debe en parte a la carencia de relaciones de calidad de las firmas con proveedores y competencia.
The Journal of Physical Chemistry A, 2000
Photodissociation of thermalized NiOH + and NiOH + (H 2 O) are examined over the visible and near... more Photodissociation of thermalized NiOH + and NiOH + (H 2 O) are examined over the visible and near-ultraviolet using time-of-flight mass spectrometry. Branching ratios and photodissociation cross sections are monitored as a function of laser wavelength. Loss of OH is the only dissociation channel observed in NiOH + , whereas loss of H 2 O and OH are present, and competitive, in the photodissociation of NiOH + (H 2 O). The photofragment spectrum of NiOH + shows absorption bands at ∼300 and ∼400 nm. An almost identical spectrum is observed for the net photodissociation of NiOH + (H 2 O). Spectroscopic thresholds taken from the photofragment spectra have been corrected to yield upper limits to the 0 K bond energies for the ions: D o 0 (Ni +-OH) e 271 (9 kJ/mol, D o 0 (NiOH +-H 2 O) e 271 (9 kJ/mol, and D o 0 (Ni + H 2 O-OH) e 334 (5 kJ/mol. Calculated B3LYP values are consistent with the experimental upper limits, but suggest that the true D o 0 (NiOH +-H 2 O) and D o 0 (Ni + H 2 O-OH) lie significantly below these upper limits. Photodissociation of NiOH + (H 2 O) near 300 nm leads to greater OH production than RRKM calculations predict, suggesting that excitation in this region leads to direct Ni +-OH bond cleavage.
The Journal of Physical Chemistry A, 2006
The photodissociation of propargyl chloride (C 3 H 3 Cl) has been studied at 193 nm. Ion imaging ... more The photodissociation of propargyl chloride (C 3 H 3 Cl) has been studied at 193 nm. Ion imaging experiments with state-selective detection of the Cl atoms and single-photon ionization of the C 3 H 3 radicals were performed, along with measurements of the Cl + C 3 H 3 and HCl + C 3 H 2 recoil kinetic energy distributions, using a scattering apparatus with electron bombardment ionization detection to resolve the competing Cl and HCl elimination channels. The experiments allow the determination of the Cl (2 P 3/2) and Cl (2 P 1/2) (hereafter Cl*) branching fractions associated with the C-Cl bond fission, which are determined to be 0.5 (0.1 for both channels. Although prior translational spectroscopy studies by others had concluded that the low velocity signal at the Cl + mass was due to daughter fragments of the HCl elimination products, the present work shows that Cl atoms are produced with a bimodal recoil kinetic energy distribution. The major C-Cl bond fission channel, with a narrow recoil kinetic energy distribution peaking near 40 kcal/mol, produces both Cl and Cl*, whereas the minor (5%) channel, partitioning much less energy to relative kinetic energy, produces only ground spin-orbit state Cl atoms. The maximum internal energy of the radicals produced in the lowrecoil-kinetic-energy channel is consistent with this channel producing electronically excited propargyl radicals. Finally, in contrast to previous studies, the present work determines the HCl recoil kinetic energy distribution and identifies the possible contribution to this spectrum from propargyl radicals cracking to C 3 + ions in the mass spectrometer.
The Journal of Physical Chemistry A, 2004
Two-color, two-photon resonant, three-photon ionization, and high-resolution photoelectron spectr... more Two-color, two-photon resonant, three-photon ionization, and high-resolution photoelectron spectroscopy are combined to characterize the photoionization dynamics of the 3pσ 2 Σ u + electronic state of NO 2. Direct photoionization of selected vibrational levels of the NO 2 3pσ 2 Σ u + state shows a strong propensity to preserve the vibrational quantum numbers of the intermediate state. Efficient methods for producing NO 2 + X 1 Σ u + (000), (010), (100), and (001) with over 95% purity are discussed. This approach is expected to be applicable to the study of the mode dependence of the effects of vibrational excitation in ion-molecule reactions involving NO 2 + .
The Journal of Physical Chemistry A, 2000
Photofragment spectra of jet-cooled MCH 2 + (M) Fe, Co, Ni) have been measured. Our investigation... more Photofragment spectra of jet-cooled MCH 2 + (M) Fe, Co, Ni) have been measured. Our investigation of NiCH 2 + represents the first reported spectroscopic study of this molecule. A spectroscopic threshold is observed for each of the three systems. In addition to imposing strict upper limits on the M +-CH 2 bond strengths, these results further the discussion concerning the interpretation of spectroscopic thresholds as thermodynamic limits. The measured upper limits are: D°0(Fe +-CH 2) e 342 (2 kJ/mol, D°0(Co +-CH 2) e 331 (2 kJ/ mol, and D°0(Ni +-CH 2) e 295 (5 kJ/mol. Three distinct, 2-nm-wide peaks are observed in the photofragment spectrum of CoCH 2 + , but the spectra lack sharp structure above threshold.
The Journal of Physical Chemistry A, 2000
Hydrated divalent nickel clusters, Ni 2+ (H 2 O) n (n) 4-7), have been generated through electros... more Hydrated divalent nickel clusters, Ni 2+ (H 2 O) n (n) 4-7), have been generated through electrospray ionization and studied with laser photofragment spectroscopy. Clusters containing six and seven water molecules dissociate by loss of either one or two water molecules. In contrast, Ni 2+ (H 2 O) 4 dissociates via charge reduction, producing H 3 O + + NiOH + (H 2 O) 2. The modest kinetic energy release in the H 3 O + product is in agreement with a saltbridge dissociation mechanism. Observed dissociation cross-sections indicate that the hexahydrated species is the probable carrier for nickel's aqueous absorption spectrum.
SIMULATION, 1990
This paper discusses an efficient method for handling time dependent boundary conditions with the... more This paper discusses an efficient method for handling time dependent boundary conditions with the DSS/2 differential equation solver. The method was evaluated by using it in the numerical solution of a diffusion problem. The proposed method is also particularly useful for boundary conditions in which only derivatives of the depend ent variables are involved. The method is based on transforming the boundary conditions at the interface to a set of algebraic equations which must be solved simultaneously at each integra tion step. Both algebraic and numerical solutions of this set of equations are discussed, and the relative merits of each one of these solutions are evaluated. The proposed method provides significant improvements in computation times and is capable of handling more complex boundary conditions as compared to other conventional methods.
Phys. Chem. Chem. Phys., 2005
Solvated cluster ions Co 21 (CH 3 OH) n (n ¼ 4-7) have been produced by electrospray and studied ... more Solvated cluster ions Co 21 (CH 3 OH) n (n ¼ 4-7) have been produced by electrospray and studied using photofragment spectroscopy. There are notable differences between the photodissociation spectra of these complexes and the analogous water complexes. Co 21 (CH 3 OH) 6 absorbs significantly more strongly than Co 21 (H 2 O) 6. The photodissociation spectra of Co 21 (CH 3 OH) n (n ¼ 4, 5 and 6) are very similar, which suggests that they share the Co 21 (CH 3 OH) 4 chromophore, with additional solvent molecules in the second shell. In contrast, our earlier studies indicate that Co 21 (H 2 O) 6 is six coordinate, and its spectrum is significantly different from that of Co 21 (H 2 O) 4. The larger clusters Co 21 (CH 3 OH) n (n ¼ 5-7) dissociate by simple loss of one or more solvent molecules. Larger clusters tend to lose more solvent molecules, especially at higher photon energies. As with the corresponding water cluster, Co 21 (CH 3 OH) 4 photodissociates by proton transfer through a salt-bridge intermediate. This is accompanied by a modest kinetic energy release of 170 kJ mol À1 and occurs with a lifetime of 145 ns.
Journal of Elastomers & Plastics, 2013
Histogram analyses of atomic force microscopy (AFM) phase images demonstrated changes in the surf... more Histogram analyses of atomic force microscopy (AFM) phase images demonstrated changes in the surface composition of ethylene propylene diene–modified (EPDM) elastomeric formulations containing polybutadiene after exposure to hydrazine. It was determined by Fourier-transform infrared (FT-IR) spectroscopic analysis that the change in the surface composition is caused by hydrogenation of the vinylic double bonds of the polybutadiene coagent, stemming from diimide generation from hydrazine. The diffusion and subsequent reaction of hydrazine with two cured EPDM elastomeric formulations were investigated by mapping FT-IR spectroscopy. The depth of diffusion and reaction was determined by monitoring changes in the intensity of the vinyl group signal from the polybutadiene in the FT-IR spectra. The FT-IR analysis of horizontal microtome specimens and vertical ‘cross section’ of the EPDM samples showed that hydrazine diffused less than 200 μm into the elastomeric materials over a period of 4...
The Journal of Chemical Physics, 1999
We report the first vibrationally resolved spectroscopic study of FeO ϩ. We observe the 0←0 and 1... more We report the first vibrationally resolved spectroscopic study of FeO ϩ. We observe the 0←0 and 1←0 bands of a 6 ⌺←X 6 ⌺ transition at 28 648.7 and 29 311 cm Ϫ1. Under slightly modified source conditions the 1←1 transition is observed at 28 473 cm Ϫ1. In addition to establishing an upper limit D 0 o (Fe ϩ-O͒р342.7 kJ/mol, our results give the first experimental measurements of the vibrational frequencies in both the ground state, 0 Љϭ838Ϯ4 cm Ϫ1 , and the excited electronic state, 0 Јϭ662 Ϯ2 cm Ϫ1. Partially resolved rotational structure underlying the vibrational peaks has been analyzed to measure the predissociation lifetime and estimate the change in molecular constants upon electronic excitation.
The Journal of Chemical Physics, 2004
The photoionization and photodissociation dynamics of H(2) and D(2) in selected rovibrational lev... more The photoionization and photodissociation dynamics of H(2) and D(2) in selected rovibrational levels of the B (1)Sigma(u) (+) and C (1)Pi(u) states have been investigated by velocity map ion imaging. The selected rotational levels of the B (1)Sigma(u) (+) and C (1)Pi(u) states are prepared by three-photon excitation from the ground state. The absorption of fourth photon results in photoionization to produce H(2)(+) X (2)Sigma(g)(+) or photodissociation to produce a ground-state H(1s) atom and an excited H atom with n >or= 2. The H(2) (+) ion can be photodissociated by absorption of a fifth photon. The resulting H(+) or D(+) ion images provide information on the vibrational state dependence of the photodissociation angular distribution of the molecular ion. The excited H(n >or= 2) atoms produced by the neutral dissociation process can also be ionized by the absorption of a fifth photon. The resulting ion images provide insight into the excited state branching ratios and angular distributions of the neutral photodissociation process. While the experimental ion images contain information on both the ionic and neutral processes, these can be separated based on constraints imposed on the fragment translational energies. The angular distribution of the rings in the ion images indicates that the neutral dissociation of molecular hydrogen and its isotopes is quite complex, and involves coupling to both doubly excited electronic states and the dissociation continua of singly excited Rydberg states.
The Journal of Chemical Physics, 2002
Specific ion-molecule reactions are used to prepare two intermediates of the FeO ϩ ϩCH 4 reaction... more Specific ion-molecule reactions are used to prepare two intermediates of the FeO ϩ ϩCH 4 reaction, and photodissociation of the jet-cooled intermediates is examined in the visible and near-ultraviolet using time-of-flight mass spectrometry. The photodissociation spectrum of the aquo iron carbene complex ͓H 2 CvFe-OH 2 ͔ ϩ shows transitions to at least four excited electronic states in the FeCH 2 ϩ chromophore, with broad vibrational structure. Photoexcitation of the insertion intermediate ͓HO-Fe-CH 3 ͔ ϩ leads to formation of FeOH ϩ ϩCH 3 and also triggers the reaction to produce Fe ϩ ϩCH 3 OH. The photodissociation spectrum of ͓HO-Fe-CH 3 ͔ ϩ presents a vibrationally resolved band involving progressions in the excited state Fe-C stretch, Fe-O stretch, and O-Fe-C bend. The change in the Fe-C bond length in ͓HO-Fe-CH 3 ͔ ϩ and ͓H 2 CvFe-OH 2 ͔ ϩ upon photoexcitation is calculated from a Franck-Condon analysis of the vibronic features observed. The analysis of the experimental results is aided by hybrid Hartree-Fock/density-functional ͑B3LYP͒ calculations on ͓HO-Fe-CH 3 ͔ ϩ and ͓H 2 CvFe-OH 2 ͔ ϩ performed to determine molecular parameters, and time-dependent density functional theory ͑TD-DFT͒ calculations on FeCH 2 ϩ to predict excited electronic states.
The Journal of Chemical Physics, 2003
The resonance enhanced ͑1ϩ1͒ photodissociation spectra of the ͑8,0͒ and ͑9,0͒ bands of the 6 ⌸ 7/... more The resonance enhanced ͑1ϩ1͒ photodissociation spectra of the ͑8,0͒ and ͑9,0͒ bands of the 6 ⌸ 7/2 ← 6 ⌺ ϩ system of FeO ϩ have been recorded. From a rotational analysis, the rotational parameters for the 6 ⌺ ϩ ground state of FeO ϩ have been obtained for the first time. The rotational constant B 0 ϭ0.5020Ϯ0.0004 cm Ϫ1 is derived, giving r 0 ϭ1.643Ϯ0.001 Å. Other molecular parameters determined for the 6 ⌺ ϩ ground state are the spin-spin coupling constant, ϭϪ0.126Ϯ0.006 cm Ϫ1 , and the spin-rotational coupling constant, ␥ϭϪ0.033Ϯ0.002 cm Ϫ1. The assignment of the upper state as 6 ⌸ 7/2 is based on the characteristic appearance of the band and on time-dependent density functional ͑TD-DFT͒ calculations performed on FeO ϩ. The reliability of the TD-DFT method in the prediction of excited states of FeO ϩ is corroborated by calculations on CrF and MnO, which have been extensively characterized either by spectroscopy or by high-level theoretical calculations.