Theoretical study of the dissociative process of the 4-chlorotoluene radical anion

The dissociation of the 4-chlorotoluene radical anion, in the corresponding arylic open-shell and chloride closed-shell species, has been studied using semiempirical and ab initio methods, in both cases ROHF and UHF calculations have been performed. It is shown that semiempirical PESs are not reliable. While, at least a 3-21g basis set is needed to obtain an ab initio single determinant global dissociative path (which is qualitatively consistent with the experimental evidence). In addition, UMP2, ROMP2, SOCI dissociative PESs are discussed, suggesting that ROHF-based methods are preferable to UHF-based ones. This is shown to depend on the spin contamination affecting the UHF wavefunction.