An investigation on the reaction mechanism of the F2+Cl2?2ClF using the B3LYP method

Abstract

The reaction mechanism of F 2 + Cl 2 → 2ClF has been investigated with the density functional theory at the B3LYP/6-311G * level. Six transition states have been found for the three possible reaction paths and verified bythe normal mode vibrational and IRC analyses. Ab initio MP2/6-311G * geometry optimizations and CCSD(T)/6-311G(2df)//MP2./6-311G * single-point energy calculations have been performed for comparison. It is found that when the F 2 (or Cl 2 ) molecule decomposes into atoms first and then the F (or Cl) atom reacts with the molecule Cl 2 (or F 2 ) nearly along the molecular axis, the energy barrier is very low. The calculated energy barrier of F attacking Cl 2 is zero and that of Cl attacking F 2 is only 15.57 kJ.mol - 1 at the B3LYP level. However, the calculated dissociation energies of F 2 and Cl 2 are as high as 145.40 and 192.48 kJ.mol - 1 , respectively. When the reaction proceeds through a bimolecular reaction mechanism, two four-center transition states are obtained and the lower energy barrier is 218.69 kJ.mol - 1 . Therefore, the title reaction F 2 + Cl 2 → 2ClF is most probably initiated from the atomization of the F 2 molecule and terminated by the reaction of F attacking Cl 2 nearly along the Cl-Cl bond. MP2 calculations lead to the same conclusion, but the geometry of TS and the energy barrier are somewhat different.