Atmospheric oxidation pathways of propane and its by-products: Acetone, acetaldehyde, and propionaldehyde

Abstract

Propane (C 3 H 8) is one of the most abundant nonmethane hydrocarbons in the atmosphere. It is a fuel widely used, derived from petroleum products during oil and natural gas processing. It can be oxidized in the atmosphere via its reactions with hydroxyl (OH) radicals and chlorine (Cl) atoms and serves as an indicator for the presence of such oxidants. During the atmospheric degradation of propane, various carbonyl compounds are formed, with acetone, acetaldehyde, and propionaldehyde among the most prominent. Carbonyl compounds are relevant because of their toxicity and ability to produce free radicals by photolysis that give rise to stable products, thus providing valuable information about atmospheric oxidation processes. The exact mechanisms of the oxidation pathways of propane have not been properly characterized, although several speculations have been made that determine the oxidation products. The present study investigates the oxidation mechanism of propane, acetone, acetaldehyde, and propionaldehyde by ab inito molecular orbital methods. Detailed pathways leading to experimentally observed products are presented. Equilibrium geometries and energetics, as well as vibrational frequencies of species, transition states, and prereactive complexes are determined at the QCISD(T)/6-311G(2df,2p)//MP2(full)/6-31G(d). Copyright 2007 by the American Geophysical Union.