Unrestricted Hartree-Fock Studies on the Dimerization Reactions of the Carbenes CH2, CHF and CF2

UHF theoretical analyses are carried out on the olefin forming dimerization reactions of the carbenes CH2 , CHF and CF,. It is shown that the UHF singlet ground state of the carbene dimer in coplaner symmetric conformations may enter into five distinct configura tions; two closed shell states, two ASDW states and one TSDW state. These five states appear at different regions of the nuclear configuration space depending on the substituents of the carbenes. A singlet olefin may dissociate into two singlet carbenes or two triplet carbenes depending on the bond angle of the carbene moieties. The two ASDW states correspond to the two different spin states of the carbene moieties, the triplet and singlet diradical states. The TSDW ground state appears at the region where the interconversion of the spin states of the carbene moieties takes place. The adiabatic potentials of the UHF configurations are calculated on various reaction paths. The distinction between the least and the non-least motion approaches is discussed.