Carlos J Cobos - Academia.edu (original) (raw)
Papers by Carlos J Cobos
The Journal of Physical Chemistry A, 2011
We have studied the reaction between pzÀCO 2 À Re(CO) 3 (bpy) and perchloric acid in acetonitrile... more We have studied the reaction between pzÀCO 2 À Re(CO) 3 (bpy) and perchloric acid in acetonitrile by following the UVÀvis and IR spectral changes in the reaction mixture. A fast equilibrium was found to be established between solvated protons, pzÀCO 2 ÀRe(CO) 3 (bpy), and the protonated intermediate [pzÀC(OH)OÀRe(CO) 3 (bpy)] + which finally yields pzÀCOOH and Re(CO) 3 (bpy)(CH 3 CN) + as reaction products. This intermediate has been characterized by UVÀvis and IR spectroscopies and by DFT calculations. The fully optimized DFT/CPCM structures for pzÀCO 2 ÀRe(CO) 3 (bpy) and [pzÀC(OH)OÀRe(CO) 3 (bpy)] + were compared with the X-ray structure of pzÀCO 2 ÀRe(CO) 3 (bpy). The structural parameters associated with the carboxyl group in the protonated intermediate are between those of pzÀCO 2 ÀRe(CO) 3 (bpy) and pzÀCOOH. Multivariate curve resolution methods were employed to obtain the spectrum of the protonated intermediate and the concentration profiles from the full matrix of time-resolved UVÀvis spectra. The proposed mechanism was numerically simulated by using RungeÀKutta methods. Model parameters were estimated by nonlinear regression fitting of the concentration profiles, yielding values of log(K) = 4.9 ( 0.3 and k = 0.16 ( 0.03 min À1 for the formation equilibrium constant and the decay rate constant of the protonated intermediate, respectively.
Journal of Physical Chemistry, 1988
diones further supports this mechanistic hypothesis. Listed in are the ketones and diones for whi... more diones further supports this mechanistic hypothesis. Listed in are the ketones and diones for which we have recently determined the temperature dependence of OH reactivity along with an indication of the type of CH3 and/or CH2 groups responsible for reactivity. Clearly, for both acetone and 2,3-butanedione, where only LY components react, a positive activation energy of approximately 1 kcal/mol is observed. For 2-butanone and 3-pentanone, where reactivity (proceeding through formation of an adduct intermediate) accounts for almost 30% of the reaction rate (at room temperature), the activation energies drop to values much closer to zero. Finally, for 2,5-hexanedione, where the majority of the molecule's reactivity involves the @CHZ groups, a strong "negative activation energy" is calculated.
Journal of Molecular Structure Theochem, May 15, 2008
Ab initio and density functional calculations have been performed on atmospheric peroxypropionyl ... more Ab initio and density functional calculations have been performed on atmospheric peroxypropionyl nitrate, C 2 H 5 C(O)OONO 2 (PPN) molecule and its radical decomposition products C 2 H 5 C(O)OO and C 2 H 5 C(O)O. Potential barriers for the internal rotations have been computed at the B3LYP/6-311++G(d,p) level of theory. Geometries, harmonic vibrational frequencies and thermochemical properties of stable rotational conformers and transition states have been calculated at the B3LYP/6-311++G(3df,3pd) and G3MP2B3 levels. For PPN, the results shown a structure in which the atoms nearest to the OAO bond are in approximately perpendicular planes, s(COON) = 85.9°. The standard enthalpies of formation at 298 K have been calculated using isodesmic reactions at the G3MP2// B3LYP/6-311++G(3df,3pd) level of theory. The resulting values for PPN, C 2 H 5 C(O)OO, and C 2 H 5 C(O)O are À66.5, À43.2, and À46.6 kcal mol À1 , respectively. Dissociation enthalpies of 31.5 and 37.5 kcal mol À1 have been predicted for the C 2 H 5 C(O)OO-NO 2 and C 2 H 5 C(O)O-ONO 2 bonds from the above enthalpies of formation. For comparative purposes, results derived from similar calculations are also reported for the peroxyacetyl nitrate, CH 3 C(O)OONO 2 (PAN) and for the CH 3 C(O)OO and CH 3 C(O)O radicals.
The Journal of Physical Chemistry a, Aug 1, 2008
The thermochemistry of all fluoro and chloro substituted germane molecules have been theoreticall... more The thermochemistry of all fluoro and chloro substituted germane molecules have been theoretically studied. Computed G3//B3LYP standard enthalpies of formation at 298 K obtained from isodesmic reaction schemes were compared with values derived via total atomization energies. Bond dissociation energies and energy barriers for the lowest dissociation pathways were estimated at 0 K. From these data, the most probable dissociation products at 0 K were predicted for the thermal decomposition reactions of the gaseous species. Calculated results are compared with experimental determinations as well as other theoretical data when available. The following isodesmic enthalpies of formation in kcal · mol -1 were calculated for 10 new germane species simultaneously substituted with fluoro and chloro atoms, for which no previously available computations were found in the literature:
Chemical Physics Letters, Nov 1, 1988
The canonical statistical adiabatic channel model is used to calculate limiting high-pressure rat... more The canonical statistical adiabatic channel model is used to calculate limiting high-pressure rate constants for the H+O 2→HO 2 reaction between 200 and 1000 K on the Lemon and Hase potential energy surface. An effective adiabatic channel potential which accounts for optimized matrix elements for the bending along the reaction path, non-separability of both the bending and HOO stretching modes, and of the J and K rotational quantum numbers is considered. The rate constant calculated at 300 K is about a factor of two smaller than a recent experimental value. An agreement better than 10% is obtained using a modified radial potential with no energy barrier for addition.
Chemical Physics, 1993
The full version of the statistical adiabatic channel model has been used for a detailed study of... more The full version of the statistical adiabatic channel model has been used for a detailed study of the title reaction at the limit of high pressure for the 100-1000 K temperature range. The calculations have been carried out on an analytic potential energy surface for the ground state of HNO developed from recent high-level ab initio data. The effects of quantum mechanical tunneling through the barriers on the adiabatic channel potentials are included in the calculations. The tunneling increases the rate of recombination by factors of 3.3, 1.7 and 1.08 at 100, 300 and 1000 K, respectively. The calculated rate constant at 300 K was found to have a difference of only 20% from the available experimental one. State-resolved rate constants are also presented. Calculations for the D+NO+DNO reaction between 100 and 400 K were also performed. The kinetic isotopic effect is calculated to decrease from 2.5 to 1.8 over this temperature range. 0301-0104/93/S 06.00 0
Influence of the essential features of the potential energy surface on the temperature dependence of the H+CH3→CH4 reaction
Reaction Kinetics and Catalysis Letters, 1991
ABSTRACT
The Journal of Physical Chemistry, 1985
The recombination reaction CH, + O2 --+ CH3O2 was studied at room temperature by laser flash phot... more The recombination reaction CH, + O2 --+ CH3O2 was studied at room temperature by laser flash photolysis over the pressure range 0.25-150 bar in the bath gases Ar and N2. Falloff curves are constructed, leading to a limiting high-pressure rate constant of k,,,, = (2.2 f 0.3) X cm3 molecule-I s-I. By use of a simplified statistical adiabatic channel model, on the basis of the measured k,,,, a set of specific rate constants k(E,J) is calculated for the unimolecular dissociation CH3O2 -CH, + O2 and compared with the reaction CH3O2 -CH30 + 0. With the derived specific rate constants, thermal rate constants for the reaction CH3 + O2 + C H 3 0 + 0 are calculated and compared with experiments.
Falloff curve and specific rate constants for the reaction NO/sub 2/ + NO/sub 2/ /r reversible/ N/sub 2/O/sub 4/
J Phys Chem, Jul 28, 1988
ABSTRACT
Canonical statistical adiabatic channel model calculations of the H + CH3 ? CH4 recombination reaction on anab initio potential energy surface. The role of the transitional modes
Int J Chem Kinet, 1989
ABSTRACT
International Journal of Chemical Kinetics, Apr 1, 1986
The influence of the effective potential energy curves on the calculation of the strong collision... more The influence of the effective potential energy curves on the calculation of the strong collision limiting low-pressure rate coefficients of thermal dissociation-recombination reactions was analyzed in terms of the factorized formalism of Troe. An analysis of 26 reactions employing a Morse potential coupled with a quasitriatomic molecular model and an explicit account of the adiabatic zero-point barriers, as originally proposed by Troe, was performed. A comparison between calculations realized with an exactly fitted looseness parameter, a, and with a standard value of Q = 1.0 A-1, indicates that the use of this last value is satisfactorily justified in the evaluation of the strong collision limiting low-pressure rate coefficients. A study in terms of restrictive relationships between the looseness and Morse parameters and ab initio radial potentials (for CH,, CH302, and HO,) was also realized. The uncertainties in the evaluation of termolecular rate coefficients due to the lack of a complete knowledge of the long-range potentials are also briefly discussed. the limiting low-pressure rate coefficients for dissociation, KO, and for recombination reactions, K,,,,o, was proposed by Troe [21. In this model, ko has been expressed in a factorized form, which allows a straightforward evaluation of each contributing factor. A major source of uncertainty at low temperatures is related to the rotational factors which require detailed information about the centrifugal barriers and thus the potential energy surface or, as rovibrational (Coriolis) coupling is neglected, the effective potential energy curve. In ref.
molecules are determined at the B3LYP, B3PW91, mPW1PW91 and B1LYP levels of the density functiona... more molecules are determined at the B3LYP, B3PW91, mPW1PW91 and B1LYP levels of the density functional theory employing a series of extended basis sets, and using Gaussian-3 model chemistries. Modified Gaussian-3 calculations, which employ accurate B3LYP/6-311 þ G(3d2f) molecular geometries and vibrational frequencies, were also performed. Heats of formation were calculated from both total atomization energies and isodesmic reaction schemes. The latter method in conjunction with Gaussian-3 models leads to the most reliable results. The best values at 298 K for ClO 3 , ClO 4 , Cl 2 O 3 and Cl 2 O 4 as derived from an average of G3//B3LYP and G3//B3LYP/6-311 þ G(3d2f) calculations are 43.1, 54.8, 31.7 and 37.4 kcal mol 21 . From calculations carried out at the G3(MP2)//B3LYP and G3(MP2)// B3LYP/6-311 þ G(3d2f) levels, heats offormation for Cl 2 O 5 , Cl 2 O 6 and Cl 2 O 7 are predicted to be 53.2, 52.2 and 61.5 kcal mol 21 . All best values are reproduced within 1 kcal mol 21 by using mPW1PW91/6-311 þ G(3d2f) isodesmic energies. Enthalpy changes for relevant Cl -O bond fission reactions are reported. Comparisons with previous thermodynamics data are made. q
Estudio de la descomposición fotoquímica del ozono. C.J. Cobos. Tesis Doctoral. Facultad de Ciencias Exactas de la UNLP, 1981
Journal of Molecular Structure: THEOCHEM, 2003
molecules are determined at the B3LYP, B3PW91, mPW1PW91 and B1LYP levels of the density functiona... more molecules are determined at the B3LYP, B3PW91, mPW1PW91 and B1LYP levels of the density functional theory employing a series of extended basis sets, and using Gaussian-3 model chemistries. Modified Gaussian-3 calculations, which employ accurate B3LYP/6-311 þ G(3d2f) molecular geometries and vibrational frequencies, were also performed. Heats of formation were calculated from both total atomization energies and isodesmic reaction schemes. The latter method in conjunction with Gaussian-3 models leads to the most reliable results. The best values at 298 K for ClO 3 , ClO 4 , Cl 2 O 3 and Cl 2 O 4 as derived from an average of G3//B3LYP and G3//B3LYP/6-311 þ G(3d2f) calculations are 43.1, 54.8, 31.7 and 37.4 kcal mol 21 . From calculations carried out at the G3(MP2)//B3LYP and G3(MP2)// B3LYP/6-311 þ G(3d2f) levels, heats offormation for Cl 2 O 5 , Cl 2 O 6 and Cl 2 O 7 are predicted to be 53.2, 52.2 and 61.5 kcal mol 21 . All best values are reproduced within 1 kcal mol 21 by using mPW1PW91/6-311 þ G(3d2f) isodesmic energies. Enthalpy changes for relevant Cl -O bond fission reactions are reported. Comparisons with previous thermodynamics data are made. q
La fotólisis del ozono a 313 nm
Anales des la Asociacion Quimica Argentina
International Journal of Chemical Kinetics
The influence of the effective potential energy curves on the calculation of the strong collision... more The influence of the effective potential energy curves on the calculation of the strong collision limiting low-pressure rate coefficients of thermal dissociation-recombination reactions was analyzed in terms of the factorized formalism of Troe. An analysis of 26 reactions employing a Morse potential coupled with a quasitriatomic molecular model and an explicit account of the adiabatic zero-point barriers, as originally proposed by Troe, was performed. A comparison between calculations realized with an exactly fitted looseness parameter, a, and with a standard value of Q = 1.0 A-1, indicates that the use of this last value is satisfactorily justified in the evaluation of the strong collision limiting low-pressure rate coefficients. A study in terms of restrictive relationships between the looseness and Morse parameters and ab initio radial potentials (for CH,, CH302, and HO,) was also realized. The uncertainties in the evaluation of termolecular rate coefficients due to the lack of a complete knowledge of the long-range potentials are also briefly discussed. the limiting low-pressure rate coefficients for dissociation, KO, and for recombination reactions, K,,,,o, was proposed by Troe [21. In this model, ko has been expressed in a factorized form, which allows a straightforward evaluation of each contributing factor. A major source of uncertainty at low temperatures is related to the rotational factors which require detailed information about the centrifugal barriers and thus the potential energy surface or, as rovibrational (Coriolis) coupling is neglected, the effective potential energy curve. In ref.
The Journal of Chemical Physics
The Journal of Physical Chemistry
The kinetics of the photochlorination of 1,1-dichloro-2,2-difluoroethylene under intermittent light
Journal of Photochemistry
ABSTRACT
The kinetics and the mechanism of ozone photolysis at 253.7 nm
Journal of Photochemistry
ABSTRACT
The Journal of Physical Chemistry A, 2011
We have studied the reaction between pzÀCO 2 À Re(CO) 3 (bpy) and perchloric acid in acetonitrile... more We have studied the reaction between pzÀCO 2 À Re(CO) 3 (bpy) and perchloric acid in acetonitrile by following the UVÀvis and IR spectral changes in the reaction mixture. A fast equilibrium was found to be established between solvated protons, pzÀCO 2 ÀRe(CO) 3 (bpy), and the protonated intermediate [pzÀC(OH)OÀRe(CO) 3 (bpy)] + which finally yields pzÀCOOH and Re(CO) 3 (bpy)(CH 3 CN) + as reaction products. This intermediate has been characterized by UVÀvis and IR spectroscopies and by DFT calculations. The fully optimized DFT/CPCM structures for pzÀCO 2 ÀRe(CO) 3 (bpy) and [pzÀC(OH)OÀRe(CO) 3 (bpy)] + were compared with the X-ray structure of pzÀCO 2 ÀRe(CO) 3 (bpy). The structural parameters associated with the carboxyl group in the protonated intermediate are between those of pzÀCO 2 ÀRe(CO) 3 (bpy) and pzÀCOOH. Multivariate curve resolution methods were employed to obtain the spectrum of the protonated intermediate and the concentration profiles from the full matrix of time-resolved UVÀvis spectra. The proposed mechanism was numerically simulated by using RungeÀKutta methods. Model parameters were estimated by nonlinear regression fitting of the concentration profiles, yielding values of log(K) = 4.9 ( 0.3 and k = 0.16 ( 0.03 min À1 for the formation equilibrium constant and the decay rate constant of the protonated intermediate, respectively.
Journal of Physical Chemistry, 1988
diones further supports this mechanistic hypothesis. Listed in are the ketones and diones for whi... more diones further supports this mechanistic hypothesis. Listed in are the ketones and diones for which we have recently determined the temperature dependence of OH reactivity along with an indication of the type of CH3 and/or CH2 groups responsible for reactivity. Clearly, for both acetone and 2,3-butanedione, where only LY components react, a positive activation energy of approximately 1 kcal/mol is observed. For 2-butanone and 3-pentanone, where reactivity (proceeding through formation of an adduct intermediate) accounts for almost 30% of the reaction rate (at room temperature), the activation energies drop to values much closer to zero. Finally, for 2,5-hexanedione, where the majority of the molecule's reactivity involves the @CHZ groups, a strong "negative activation energy" is calculated.
Journal of Molecular Structure Theochem, May 15, 2008
Ab initio and density functional calculations have been performed on atmospheric peroxypropionyl ... more Ab initio and density functional calculations have been performed on atmospheric peroxypropionyl nitrate, C 2 H 5 C(O)OONO 2 (PPN) molecule and its radical decomposition products C 2 H 5 C(O)OO and C 2 H 5 C(O)O. Potential barriers for the internal rotations have been computed at the B3LYP/6-311++G(d,p) level of theory. Geometries, harmonic vibrational frequencies and thermochemical properties of stable rotational conformers and transition states have been calculated at the B3LYP/6-311++G(3df,3pd) and G3MP2B3 levels. For PPN, the results shown a structure in which the atoms nearest to the OAO bond are in approximately perpendicular planes, s(COON) = 85.9°. The standard enthalpies of formation at 298 K have been calculated using isodesmic reactions at the G3MP2// B3LYP/6-311++G(3df,3pd) level of theory. The resulting values for PPN, C 2 H 5 C(O)OO, and C 2 H 5 C(O)O are À66.5, À43.2, and À46.6 kcal mol À1 , respectively. Dissociation enthalpies of 31.5 and 37.5 kcal mol À1 have been predicted for the C 2 H 5 C(O)OO-NO 2 and C 2 H 5 C(O)O-ONO 2 bonds from the above enthalpies of formation. For comparative purposes, results derived from similar calculations are also reported for the peroxyacetyl nitrate, CH 3 C(O)OONO 2 (PAN) and for the CH 3 C(O)OO and CH 3 C(O)O radicals.
The Journal of Physical Chemistry a, Aug 1, 2008
The thermochemistry of all fluoro and chloro substituted germane molecules have been theoreticall... more The thermochemistry of all fluoro and chloro substituted germane molecules have been theoretically studied. Computed G3//B3LYP standard enthalpies of formation at 298 K obtained from isodesmic reaction schemes were compared with values derived via total atomization energies. Bond dissociation energies and energy barriers for the lowest dissociation pathways were estimated at 0 K. From these data, the most probable dissociation products at 0 K were predicted for the thermal decomposition reactions of the gaseous species. Calculated results are compared with experimental determinations as well as other theoretical data when available. The following isodesmic enthalpies of formation in kcal · mol -1 were calculated for 10 new germane species simultaneously substituted with fluoro and chloro atoms, for which no previously available computations were found in the literature:
Chemical Physics Letters, Nov 1, 1988
The canonical statistical adiabatic channel model is used to calculate limiting high-pressure rat... more The canonical statistical adiabatic channel model is used to calculate limiting high-pressure rate constants for the H+O 2→HO 2 reaction between 200 and 1000 K on the Lemon and Hase potential energy surface. An effective adiabatic channel potential which accounts for optimized matrix elements for the bending along the reaction path, non-separability of both the bending and HOO stretching modes, and of the J and K rotational quantum numbers is considered. The rate constant calculated at 300 K is about a factor of two smaller than a recent experimental value. An agreement better than 10% is obtained using a modified radial potential with no energy barrier for addition.
Chemical Physics, 1993
The full version of the statistical adiabatic channel model has been used for a detailed study of... more The full version of the statistical adiabatic channel model has been used for a detailed study of the title reaction at the limit of high pressure for the 100-1000 K temperature range. The calculations have been carried out on an analytic potential energy surface for the ground state of HNO developed from recent high-level ab initio data. The effects of quantum mechanical tunneling through the barriers on the adiabatic channel potentials are included in the calculations. The tunneling increases the rate of recombination by factors of 3.3, 1.7 and 1.08 at 100, 300 and 1000 K, respectively. The calculated rate constant at 300 K was found to have a difference of only 20% from the available experimental one. State-resolved rate constants are also presented. Calculations for the D+NO+DNO reaction between 100 and 400 K were also performed. The kinetic isotopic effect is calculated to decrease from 2.5 to 1.8 over this temperature range. 0301-0104/93/S 06.00 0
Influence of the essential features of the potential energy surface on the temperature dependence of the H+CH3→CH4 reaction
Reaction Kinetics and Catalysis Letters, 1991
ABSTRACT
The Journal of Physical Chemistry, 1985
The recombination reaction CH, + O2 --+ CH3O2 was studied at room temperature by laser flash phot... more The recombination reaction CH, + O2 --+ CH3O2 was studied at room temperature by laser flash photolysis over the pressure range 0.25-150 bar in the bath gases Ar and N2. Falloff curves are constructed, leading to a limiting high-pressure rate constant of k,,,, = (2.2 f 0.3) X cm3 molecule-I s-I. By use of a simplified statistical adiabatic channel model, on the basis of the measured k,,,, a set of specific rate constants k(E,J) is calculated for the unimolecular dissociation CH3O2 -CH, + O2 and compared with the reaction CH3O2 -CH30 + 0. With the derived specific rate constants, thermal rate constants for the reaction CH3 + O2 + C H 3 0 + 0 are calculated and compared with experiments.
Falloff curve and specific rate constants for the reaction NO/sub 2/ + NO/sub 2/ /r reversible/ N/sub 2/O/sub 4/
J Phys Chem, Jul 28, 1988
ABSTRACT
Canonical statistical adiabatic channel model calculations of the H + CH3 ? CH4 recombination reaction on anab initio potential energy surface. The role of the transitional modes
Int J Chem Kinet, 1989
ABSTRACT
International Journal of Chemical Kinetics, Apr 1, 1986
The influence of the effective potential energy curves on the calculation of the strong collision... more The influence of the effective potential energy curves on the calculation of the strong collision limiting low-pressure rate coefficients of thermal dissociation-recombination reactions was analyzed in terms of the factorized formalism of Troe. An analysis of 26 reactions employing a Morse potential coupled with a quasitriatomic molecular model and an explicit account of the adiabatic zero-point barriers, as originally proposed by Troe, was performed. A comparison between calculations realized with an exactly fitted looseness parameter, a, and with a standard value of Q = 1.0 A-1, indicates that the use of this last value is satisfactorily justified in the evaluation of the strong collision limiting low-pressure rate coefficients. A study in terms of restrictive relationships between the looseness and Morse parameters and ab initio radial potentials (for CH,, CH302, and HO,) was also realized. The uncertainties in the evaluation of termolecular rate coefficients due to the lack of a complete knowledge of the long-range potentials are also briefly discussed. the limiting low-pressure rate coefficients for dissociation, KO, and for recombination reactions, K,,,,o, was proposed by Troe [21. In this model, ko has been expressed in a factorized form, which allows a straightforward evaluation of each contributing factor. A major source of uncertainty at low temperatures is related to the rotational factors which require detailed information about the centrifugal barriers and thus the potential energy surface or, as rovibrational (Coriolis) coupling is neglected, the effective potential energy curve. In ref.
molecules are determined at the B3LYP, B3PW91, mPW1PW91 and B1LYP levels of the density functiona... more molecules are determined at the B3LYP, B3PW91, mPW1PW91 and B1LYP levels of the density functional theory employing a series of extended basis sets, and using Gaussian-3 model chemistries. Modified Gaussian-3 calculations, which employ accurate B3LYP/6-311 þ G(3d2f) molecular geometries and vibrational frequencies, were also performed. Heats of formation were calculated from both total atomization energies and isodesmic reaction schemes. The latter method in conjunction with Gaussian-3 models leads to the most reliable results. The best values at 298 K for ClO 3 , ClO 4 , Cl 2 O 3 and Cl 2 O 4 as derived from an average of G3//B3LYP and G3//B3LYP/6-311 þ G(3d2f) calculations are 43.1, 54.8, 31.7 and 37.4 kcal mol 21 . From calculations carried out at the G3(MP2)//B3LYP and G3(MP2)// B3LYP/6-311 þ G(3d2f) levels, heats offormation for Cl 2 O 5 , Cl 2 O 6 and Cl 2 O 7 are predicted to be 53.2, 52.2 and 61.5 kcal mol 21 . All best values are reproduced within 1 kcal mol 21 by using mPW1PW91/6-311 þ G(3d2f) isodesmic energies. Enthalpy changes for relevant Cl -O bond fission reactions are reported. Comparisons with previous thermodynamics data are made. q
Estudio de la descomposición fotoquímica del ozono. C.J. Cobos. Tesis Doctoral. Facultad de Ciencias Exactas de la UNLP, 1981
Journal of Molecular Structure: THEOCHEM, 2003
molecules are determined at the B3LYP, B3PW91, mPW1PW91 and B1LYP levels of the density functiona... more molecules are determined at the B3LYP, B3PW91, mPW1PW91 and B1LYP levels of the density functional theory employing a series of extended basis sets, and using Gaussian-3 model chemistries. Modified Gaussian-3 calculations, which employ accurate B3LYP/6-311 þ G(3d2f) molecular geometries and vibrational frequencies, were also performed. Heats of formation were calculated from both total atomization energies and isodesmic reaction schemes. The latter method in conjunction with Gaussian-3 models leads to the most reliable results. The best values at 298 K for ClO 3 , ClO 4 , Cl 2 O 3 and Cl 2 O 4 as derived from an average of G3//B3LYP and G3//B3LYP/6-311 þ G(3d2f) calculations are 43.1, 54.8, 31.7 and 37.4 kcal mol 21 . From calculations carried out at the G3(MP2)//B3LYP and G3(MP2)// B3LYP/6-311 þ G(3d2f) levels, heats offormation for Cl 2 O 5 , Cl 2 O 6 and Cl 2 O 7 are predicted to be 53.2, 52.2 and 61.5 kcal mol 21 . All best values are reproduced within 1 kcal mol 21 by using mPW1PW91/6-311 þ G(3d2f) isodesmic energies. Enthalpy changes for relevant Cl -O bond fission reactions are reported. Comparisons with previous thermodynamics data are made. q
La fotólisis del ozono a 313 nm
Anales des la Asociacion Quimica Argentina
International Journal of Chemical Kinetics
The influence of the effective potential energy curves on the calculation of the strong collision... more The influence of the effective potential energy curves on the calculation of the strong collision limiting low-pressure rate coefficients of thermal dissociation-recombination reactions was analyzed in terms of the factorized formalism of Troe. An analysis of 26 reactions employing a Morse potential coupled with a quasitriatomic molecular model and an explicit account of the adiabatic zero-point barriers, as originally proposed by Troe, was performed. A comparison between calculations realized with an exactly fitted looseness parameter, a, and with a standard value of Q = 1.0 A-1, indicates that the use of this last value is satisfactorily justified in the evaluation of the strong collision limiting low-pressure rate coefficients. A study in terms of restrictive relationships between the looseness and Morse parameters and ab initio radial potentials (for CH,, CH302, and HO,) was also realized. The uncertainties in the evaluation of termolecular rate coefficients due to the lack of a complete knowledge of the long-range potentials are also briefly discussed. the limiting low-pressure rate coefficients for dissociation, KO, and for recombination reactions, K,,,,o, was proposed by Troe [21. In this model, ko has been expressed in a factorized form, which allows a straightforward evaluation of each contributing factor. A major source of uncertainty at low temperatures is related to the rotational factors which require detailed information about the centrifugal barriers and thus the potential energy surface or, as rovibrational (Coriolis) coupling is neglected, the effective potential energy curve. In ref.
The Journal of Chemical Physics
The Journal of Physical Chemistry
The kinetics of the photochlorination of 1,1-dichloro-2,2-difluoroethylene under intermittent light
Journal of Photochemistry
ABSTRACT
The kinetics and the mechanism of ozone photolysis at 253.7 nm
Journal of Photochemistry
ABSTRACT