Ligand exchange reactions of sodium cation complexes examined using guided ion beam mass spectrometry: Relative and absolute dissociation free energies and entropies

Jay Amicangelo, P. B. Armentrout

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Abstract

Guided ion beam mass spectrometry is used to study the ligand exchange reactions of Na +L 1 with L 2, where L 1, L 2 = H 2O, C 6H 6, CH 3OH, CH 3OCH 3, NH 3, and C 2H 5OH, as a function of kinetic energy. For the endothermic ligand exchange reactions, reaction endothermicities are obtained by analyzing the kinetic energy dependence of the cross sections using our empirical threshold modeling equation. The thresholds are found to be systematically higher than values previously determined using competitive CID experiments by 0.07 0.2 eV. An analysis of the endothermic cross sections using a bimolecular, polyatomic phase theory model and a competitive, bimolecular RRKM model demonstrates that the systematic deviations result from a competitive shift between the thermoneutral reactions back to the reactants and the endothermic reactions to the ligand exchange products. For all reactions, thermal rate constants, k(298), are determined by modeling the cross sections in the low-energy region and integrating the model over a Maxwell-Boltzmann distribution of relative energies. From the rate constants for the forward and reverse reactions, equilibrium constants and relative free energies at 298 K for the ligand exchange processes are determined. The relative free energies are converted to absolute Na +-L dissociation free energies, ΔG 298, by minimizing the differences with a set of ΔG 298 values obtained from equilibrium studies using FT-ICR mass spectrometry. Comparisons are made to previous experimental and theoretical absolute Na +-L dissociation free energies from several sources. Using the absolute Na +-L dissociation free energies from this work and absolute Na +-L dissociation enthalpies measured previously in our laboratory, dissociation entropies are determined for the Na +-L complexes.

Original languageEnglish (US)
Pages (from-to)10698-10713
Number of pages16
JournalJournal of Physical Chemistry A
Volume108
Issue number48
DOIs
StatePublished - Dec 2 2004

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Ion beams
Free energy
Mass spectrometry
Cations
Entropy
mass spectroscopy
Sodium
ion beams
free energy
sodium
dissociation
entropy
Ligands
cations
ligands
Kinetic energy
Rate constants
cross sections
kinetic energy
charge injection devices

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry

Cite this

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title = "Ligand exchange reactions of sodium cation complexes examined using guided ion beam mass spectrometry: Relative and absolute dissociation free energies and entropies",
abstract = "Guided ion beam mass spectrometry is used to study the ligand exchange reactions of Na +L 1 with L 2, where L 1, L 2 = H 2O, C 6H 6, CH 3OH, CH 3OCH 3, NH 3, and C 2H 5OH, as a function of kinetic energy. For the endothermic ligand exchange reactions, reaction endothermicities are obtained by analyzing the kinetic energy dependence of the cross sections using our empirical threshold modeling equation. The thresholds are found to be systematically higher than values previously determined using competitive CID experiments by 0.07 0.2 eV. An analysis of the endothermic cross sections using a bimolecular, polyatomic phase theory model and a competitive, bimolecular RRKM model demonstrates that the systematic deviations result from a competitive shift between the thermoneutral reactions back to the reactants and the endothermic reactions to the ligand exchange products. For all reactions, thermal rate constants, k(298), are determined by modeling the cross sections in the low-energy region and integrating the model over a Maxwell-Boltzmann distribution of relative energies. From the rate constants for the forward and reverse reactions, equilibrium constants and relative free energies at 298 K for the ligand exchange processes are determined. The relative free energies are converted to absolute Na +-L dissociation free energies, ΔG 298, by minimizing the differences with a set of ΔG 298 values obtained from equilibrium studies using FT-ICR mass spectrometry. Comparisons are made to previous experimental and theoretical absolute Na +-L dissociation free energies from several sources. Using the absolute Na +-L dissociation free energies from this work and absolute Na +-L dissociation enthalpies measured previously in our laboratory, dissociation entropies are determined for the Na +-L complexes.",
author = "Jay Amicangelo and Armentrout, {P. B.}",
year = "2004",
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T1 - Ligand exchange reactions of sodium cation complexes examined using guided ion beam mass spectrometry

T2 - Relative and absolute dissociation free energies and entropies

AU - Amicangelo, Jay

AU - Armentrout, P. B.

PY - 2004/12/2

Y1 - 2004/12/2

N2 - Guided ion beam mass spectrometry is used to study the ligand exchange reactions of Na +L 1 with L 2, where L 1, L 2 = H 2O, C 6H 6, CH 3OH, CH 3OCH 3, NH 3, and C 2H 5OH, as a function of kinetic energy. For the endothermic ligand exchange reactions, reaction endothermicities are obtained by analyzing the kinetic energy dependence of the cross sections using our empirical threshold modeling equation. The thresholds are found to be systematically higher than values previously determined using competitive CID experiments by 0.07 0.2 eV. An analysis of the endothermic cross sections using a bimolecular, polyatomic phase theory model and a competitive, bimolecular RRKM model demonstrates that the systematic deviations result from a competitive shift between the thermoneutral reactions back to the reactants and the endothermic reactions to the ligand exchange products. For all reactions, thermal rate constants, k(298), are determined by modeling the cross sections in the low-energy region and integrating the model over a Maxwell-Boltzmann distribution of relative energies. From the rate constants for the forward and reverse reactions, equilibrium constants and relative free energies at 298 K for the ligand exchange processes are determined. The relative free energies are converted to absolute Na +-L dissociation free energies, ΔG 298, by minimizing the differences with a set of ΔG 298 values obtained from equilibrium studies using FT-ICR mass spectrometry. Comparisons are made to previous experimental and theoretical absolute Na +-L dissociation free energies from several sources. Using the absolute Na +-L dissociation free energies from this work and absolute Na +-L dissociation enthalpies measured previously in our laboratory, dissociation entropies are determined for the Na +-L complexes.

AB - Guided ion beam mass spectrometry is used to study the ligand exchange reactions of Na +L 1 with L 2, where L 1, L 2 = H 2O, C 6H 6, CH 3OH, CH 3OCH 3, NH 3, and C 2H 5OH, as a function of kinetic energy. For the endothermic ligand exchange reactions, reaction endothermicities are obtained by analyzing the kinetic energy dependence of the cross sections using our empirical threshold modeling equation. The thresholds are found to be systematically higher than values previously determined using competitive CID experiments by 0.07 0.2 eV. An analysis of the endothermic cross sections using a bimolecular, polyatomic phase theory model and a competitive, bimolecular RRKM model demonstrates that the systematic deviations result from a competitive shift between the thermoneutral reactions back to the reactants and the endothermic reactions to the ligand exchange products. For all reactions, thermal rate constants, k(298), are determined by modeling the cross sections in the low-energy region and integrating the model over a Maxwell-Boltzmann distribution of relative energies. From the rate constants for the forward and reverse reactions, equilibrium constants and relative free energies at 298 K for the ligand exchange processes are determined. The relative free energies are converted to absolute Na +-L dissociation free energies, ΔG 298, by minimizing the differences with a set of ΔG 298 values obtained from equilibrium studies using FT-ICR mass spectrometry. Comparisons are made to previous experimental and theoretical absolute Na +-L dissociation free energies from several sources. Using the absolute Na +-L dissociation free energies from this work and absolute Na +-L dissociation enthalpies measured previously in our laboratory, dissociation entropies are determined for the Na +-L complexes.

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