Ab initio MO calculations on potential energy surfaces of CCl4, is a C-2v contact ion pair an isomer of T-d-CCl4?

Ab initio molecular orbital (MO) calculations have been carried out for the ground-state potential energy surface of the CCl4 molecule. It has been fo und that there is no local minimum corresponding to a C-2v contact ion CCl3 +... Cl- structure, which was previously reported to be an isomer of the mo st stable T-d-CCl4 molecule at the restricted Hartree-Fock level of theory. The primary failure of the previous study is that harmonic vibrational ana lyses as well as a check on instability for Hartree-Fock wavefunctions were not carried out. Configuration interaction calculations with single and do uble substitutions have been carried out to obtain qualitative features of excited-state potential energy surfaces and a local minimum corresponding t o the ion pair structure has been found on the singlet excited-state surfac e. (C) 1999 Elsevier Science Ltd. All rights reserved.