TY  - JOUR
T1  - Thermochemical Analyses of Sulphur Compounds: Implications for Atmospheric Sulphur Oxidation
AU - , Anselm I. Igbafe AU - , Linda L. Jewell AU - , Stuart J. Piketh 
JO  - Research Journal of Applied Sciences
VL  - 3
IS  - 5
SP  - 393
EP  - 406
PY  - 2008
DA  - 2001/08/19
SN  - 1815-932x
DO  - rjasci.2008.393.406
UR  - https://makhillpublications.co/view-article.php?doi=rjasci.2008.393.406
KW  - Thermochemistry (analysis)
KW  -energies
KW  -sulphur
KW  -atmosphere
KW  -reactions
AB  - A theoretical study of the thermochemical properties of some common sulphur species present in the atmosphere including the intermediates and end-product of their transformation is reported here. These properties were obtained from the approximation of the Schr&ouml;dinger equation<SUP> </SUP>as applied in Gaussian 03 (G03) model chemistry package. Analyses of the chemical reaction equilibrium for a variety of atmospheric sulphur transformations were investigated with a view to establish the thermodynamically favourable reaction pathways over ambient tropospheric temperature range of between -50 and +50°C. Seven high-energy accuracy model chemistries methods integrated in G03 comprising several <I>ab initio </I>methods and density functional theory (DFT) methods were applied for the computation. The computational methods were tested with a number of basis sets to yield values approximating those of experimental observations. Of all chosen methods, the complete basis set (CBS-Q) method was observed to closely approximate the experimentally determined thermodynamic enthalpies and Gibbs free energies of reactions. The CBS-Q method produced a mean absolute deviation (MAD) of 1.08% as against experimental data. Of the gas-phase and aqueous-phase reactions about 80 and 59.6%, respectively will most likely attain equilibrium over a temperature range of between -100 and +100°C. Whilst about 15 and 23.4% will not like reach equilibrium the specified temperature range and about 5 and 17% may attain equilibrium at higher temperatures above 20°C. The 4 most important oxidising species involved in the gas-phase reactions of atmospheric SO<SUB>2 </SUB>have been characterized in an order of increasing oxidant’s potentials in the form CH<SUB>3</SUB>O<SUB>2</SUB>* &lt; HO<SUB>2</SUB>* &lt; OH* &lt; O*.
ER  -