THEORETICAL PROBATION OF FCLCO...CL-2 MOLECULAR-COMPLEX - POST-HARTREE-FOCK STUDIES ON MOLECULAR-STRUCTURES, STABILITIES AND VIBRATIONAL HARMONIC FREQUENCIES

Potential energy surfaces of the weak FClCO...Cl-2 complex were studie d using ab initio post Hartree-Fock theory at the MP2 and MP4 levels w ith 6-311G(d) and 6-311G(2d) basis sets. Two minimum energy conformati ons, first-order transition state and two second-order transition stru ctures were found. The minimum energy forms (C and T) are separated by a small (less than 0.5 kcal/mol) barrier. At the MP2/6-311G(d) level their relative stabilities amount to -0.63 and -0.60 kcal/mol for C an d T conformers, respectively, where at the MP2/6-311G(2d) approximatio n stabilities of both forms rise to -1.09 and -1.21 kcal/mol. The harm onic vibrational frequencies were calculated and compared with availab le experimental data.