The Thermodynamics of the Elusive HO3 Radical

See allHide authors and affiliations

Science  04 Jun 2010:
Vol. 328, Issue 5983, pp. 1258-1262
DOI: 10.1126/science.1184459

You are currently viewing the abstract.

View Full Text


The role of HO3 as a temporary reservoir of atmospheric OH radicals remains an open question largely because of the considerable uncertainty in the value of the dissociation energy of the HO−O2 bond (D0) or, equivalently, the standard enthalpy of formation of HO3 (ΔfH°). Using a supersonic flow apparatus, we have observed by means of laser-induced fluorescence the decay of OH radicals in the presence of O2 at temperatures between 55.7 and 110.8 kelvin (K). Between 87.4 and 99.8 K, the OH concentration approached a nonzero value at long times, allowing equilibrium constants for the reaction with O2 to be calculated. Using expressions for the equilibrium constant from classical and statistical thermodynamics, and values of partition functions and standard entropies calculated from spectroscopic data, we derived values of D0 = (12.3 ± 0.3) kilojoules per mole and ΔfH° (298 K) = (19.3 ± 0.5) kilojoules per mole. The atmospheric implications of HO3 formation are therefore very slight.

View Full Text