The dynamics of chlorine-atom reactions with polyatomic organic molecules

Chlorine atoms react with a variety of organic molecules by abstraction of an H atom, making HCl and a radical co-product, and investigations of these reactions provide a large and valuable body of data for improved fundamental understanding of the mechanisms of reactions involving polyatomic molecules. The kinetics and dynamics of reactions of Cl atoms with alkanes have been extensively studied both by experimental and computational methods, and the key outcomes and conclusions are reviewed. These reactions serve as benchmarks for the interpretation of recent experimental data on the dynamics of reactions of Cl atoms with heteroatom functionalized organic molecules such as alcohols, ethers, amines, alkyl halides and thiols. Although bearing many similarities to the dynamics of the alkane reactions, significant differences are found: in particular, the extent of HCl rotational excitation from reactions of Cl atoms with the functionalized molecules is much greater than the very cold rotational distributions obtained for H-atom abstraction from simple alkanes such as methane, ethane, propane and butane. These observations and the scattering dynamics are discussed in terms of reaction energetics, barriers and transition state geometries, and evidence is presented for post-transition-state interactions between the separating HCl and polar organic radical for which the HCl rotation appears to be a sensitive probe.