We have used free electron laser (FEL) at the IR FEL Research Center, Research Institute for Science and Technology, Tokyo University of Science, Japan. The multiphoton absorption of infrared radiation induced dissociation of phenyltrifluorosilane (PhSiF3) in a batch reactor. End product analysis from IR MPD of neat PhSiF3 and the mixture of PhSiF3 and Br-2 shows that the main dissociation channels are (1) the elimination of SiF3 and (2) the elimination of H. Silicon isotopes have been enriched under the FEL irradiation of neat PhSiF3 at 961 cm(-1) (abundance of Si-30 in PhSiF3 Was increased from 3.10 +/- 0.03% to 12.3 +/- 0.1%) and 925 cm(-1) (abundance of Si-28 in PhSiF3, was increased from 92.2 +/- 0.9% to 96.5 +/- 0.9%).