Kinetic and theoretical study of the reaction of Cl atoms with a series of linear thiols

The reactions of Cl with a series of linear thiols: 1-propanethiol (k(1)), 1-butanethiol (k(2)), and 1-pentanethiol (k(3)) were investigated as a function of temperature (in the range of 268-379 K) and pressure (in the range of 50-200 Torr) by laser photolysis-resonance fluorescence. Only 1-propanethiol has previously been studied, but at 1 Torr of total pressure. The derived Arrhenius expressions obtained using our kinetic data were as follows: k(1)=(3.97+/-0.44)x10(-11) exp[(410+/-36)T], k(2)=(1.01+/-0.16)x10(-10) exp[(146+/-23)T], and k(3)=(1.28+/-0.10)x10(-10) exp[(129+/-25)T] (in units of cm(3) molecule(-1) s(-1)). Moreover, a theoretical insight into mechanisms of these reactions has also been pursued through ab initio Moller-Plesset second-order perturbation treatment calculations with 6-311G(**) basis set. Optimized geometries have been obtained for transition states and molecular complexes appearing along the different reaction pathways. Furthermore, molecular energies have been calculated at QCISD(T) level in order to get an estimation of the activation energies. Finally, the nature of the molecular complexes and transitions states is analyzed by using kinetic-potential and natural bond orbital total energy decomposition schemes.