Ab initio MO calculations on potential energy surfaces of CCl4, is a C2v contact ion pair an isomer of Td–CCl4?

Abstract

Abstract Ab initio molecular orbital (MO) calculations have been carried out for the ground-state potential energy surface of the CCl 4 molecule. It has been found that there is no local minimum corresponding to a C 2v contact ion CCl + 3 ···Cl − structure, which was previously reported to be an isomer of the most stable T d –CCl 4 molecule at the restricted Hartree–Fock level of theory. The primary failure of the previous study is that harmonic vibrational analyses as well as a check on instability for Hartree–Fock wavefunctions were not carried out. Configuration interaction calculations with single and double substitutions have been carried out to obtain qualitative features of excited-state potential energy surfaces and a local minimum corresponding to the ion pair structure has been found on the singlet excited-state surface.