The　B3LYP　calculations　of　density　functional　theory　with　6-311+G(3df)　basis　set　level　have　been　used　to　investigate　the　equilibrium　structures　and　intramolecular　rearrangement　reactions　of　the　linear　CISSF　and　branched　SSCIF　isomers.　The　calculated　results　show　that　the　linear　structure　is　more　stable　than　the　branched　one　(by　31.3　kJ-mol(-1)　corrected　with　ZPVE)　energetically　and　the　agreement　with　available　experimental　values　is　satisfactory.　The　predicted　energy　barriers　for　the　intramolecular　F　and　C1　atom　transfer　isomerization　processes　are　126.4　and　175.8　kJ.mol(-1),　respectively.　The　isomerization　process　is　unlikely　to　proceed　via　unimolecular　channel　because　of　the　much　higher　energy　barriers.