Gene/Protein
Disease
Symptom
Drug
Enzyme
Compound
Pivot Concepts:
Gene/Protein
Disease
Symptom
Drug
Enzyme
Compound
Target Concepts:
Gene/Protein
Disease
Symptom
Drug
Enzyme
Compound
Query: UMLS:C0027960 (
mole
)
21,279
document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)
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
(Delta(f)H;{\overline{);\circ }}$$). Using a supersonic flow apparatus, we have observed by means of laser-induced fluorescence the decay of OH radicals in the presence of O2 at temperatures between 55.7 and 110.8 kelvin (K). Between 87.4 and 99.8 K, the OH concentration approached a nonzero value at long times, allowing equilibrium constants for the reaction with O2 to be calculated. Using expressions for the equilibrium constant from classical and statistical thermodynamics, and values of partition functions and standard entropies calculated from spectroscopic data, we derived values of D0 = (12.3 +/- 0.3) kilojoules per
mole
and Delta(f)H;{\overline{);\circ }}$$ (298 K) = (19.3 +/- 0.5) kilojoules per
mole
. The atmospheric implications of
HO3
formation are therefore very slight.
...
PMID:The thermodynamics of the elusive HO3 radical. 2052 71
