An ab initio MO study was performed to investigate the potential energy surface for reaction H+ClF→HCl+F. Two transition states were found on this surface and from each of them an IRC calculation was followed. With all the information we have got, we come to the conclusion that there are two minimum energy paths for the formation of HCl. Potential energy barriers were determined with H attacking Cl atom of ClF at various angels, and by doing so, we have explained the reason for microscopic branching on the potential energy surface.

Key words: HYDROGEN, AB INITIO CALCULATION, MOLECULAR ORBITAL THEORY, TRANSITION STATE THEORY, POTENTIAL ENERGY SURFACES