Density functional calculations have been used to investigate adsorption and decomposition of 1-propanethiol on the Ga-rich GaAs (001) Surface. The dissociative adsorption of I-propanethiol on GaAs (001) to the chemisorbed propanethiolate and hydrogen was predicted to be quite facile. Followed by the C-S bond scission of the propanethiolate species, the surface propyl species was formed with a barrier of 47.2 kcal/mol for the low-energy route. The propyl species is an important precursor to propane through the C-H bond Coupling and to propene via the beta-H elimination. Predicted activation free energies for the Surface processes from the propyl species to propane and propene are 45.2 and 37.0 kcal/mol at 298.1 K, respectively, while the corresponding overall Gibbs free energies of reaction Delta G are -49.3 and -21.2 kcal/mol relative to free I-propanethiol. Therefore, both reaction routes ire competitive, resulting in a product Mixture, although the beta-H elimination from the propyl species is initially remarkably favorable dynamically. Oil the basis Of our calculations, detailed mechanisms for adsorption and thermal decomposition of I-propanethiol oil the GaAs (001) surface were proposed, and the calculated results show good agreement with experimental observations,