Thermochemistry of Aqueous Hydroxyl Radical from Advances in Photoacoustic Calorimetry and ab Initio Continuum Solvation Theory

Tom Autrey, Aaron K. Brown, Donald M. Camaioni, Michel Dupuis, Nancy S. Foster, April Getty

Research output: Contribution to journalArticle

28 Citations (Scopus)

Abstract

Photoacoustic signals from dilute (∼30 mM) solutions of H2O2 were measured over the temperature range from 10 to 45 °C to obtain the reaction enthalpy and volume change for H2O2(aq) → 2 OH(aq) from which we ultimately determined ΔfG°, ΔfH° and partial molal volume, v°, of OH (aq). We find ΔrH = 46.8 ± 1.4 kcal/mol, which is 4 kcal/mol smaller than the gas-phase bond energy, and ΔVr = 6.5 ± 0.4 mL/mol. The v° for OH in water is 14.4 ± 0.4 mL/ml: smaller than the v° of water. Using ab intio continuum theory, the hydration free energy is calculated to be ?3.9 ± 0.3 kcal/mol (for standard states in number density concentration units) by a novel approach devised to capture in the definition of the solute cavity the strength and specific interactions of the solute with a water solvent molecule. The shape of the cavity is defined by "rolling" a three-dimensional electron density isocontour of water on the ab initio water?OH minimum interaction surface. The value of the contour is selected to reproduce the volume of OH in water. We obtain for OH(aq): ΔfH° = ?0.2 ± 1.4 and ΔfG° = 5.8 ± 0.4 kcal/mol that are in agreement with literature values. The results provide confidence in the pulsed PAC technique for measuring aqueous thermochemistry of radicals and open the way to obtaining thermochemistry for most radicals that can be formed by reaction of OH with aqueous substrates while advancing the field of continuum solvation theory toward ab initio-defined solute cavities.

Original languageEnglish
Pages (from-to)3680-3681
Number of pages2
JournalJournal of the American Chemical Society
Volume126
Issue number12
DOIs
Publication statusPublished - Mar 31 2004

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Thermochemistry
Calorimetry
Photoacoustic effect
Solvation
Hydroxyl Radical
Water
Hydration
Free energy
Carrier concentration
Enthalpy
Gases
Electrons
Molecules
Temperature
Substrates

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

Thermochemistry of Aqueous Hydroxyl Radical from Advances in Photoacoustic Calorimetry and ab Initio Continuum Solvation Theory. / Autrey, Tom; Brown, Aaron K.; Camaioni, Donald M.; Dupuis, Michel; Foster, Nancy S.; Getty, April.

In: Journal of the American Chemical Society, Vol. 126, No. 12, 31.03.2004, p. 3680-3681.

Research output: Contribution to journalArticle

Autrey, Tom ; Brown, Aaron K. ; Camaioni, Donald M. ; Dupuis, Michel ; Foster, Nancy S. ; Getty, April. / Thermochemistry of Aqueous Hydroxyl Radical from Advances in Photoacoustic Calorimetry and ab Initio Continuum Solvation Theory. In: Journal of the American Chemical Society. 2004 ; Vol. 126, No. 12. pp. 3680-3681.
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