Laser photolysis-resonance fluorescence was used for the first time to investigate the reaction of ethanethiol with atmospheric relevant Cl atoms as a function of temperature and pressure. Kinetic data obtained were used to derive an Arrhenius expression. Moreover, a mechanism is proposed on the base of ab initio MP2/6-311G** calculations. Activation energies have been estimated through QCISD(T) molecular energies. Accordingly, our results predict, for the first time, two nearly energy-equivalent channels for H-abstraction from CH3CH2SH under attack by CI, one showing attack along H-S bond whereas the other exhibits attack along H-C-alpha bond. (c) 2007 Elsevier B.V. All rights reserved.