ABINITIO MOLECULAR-ORBITAL STUDY OF THE ELECTRONIC AND GEOMETRIC STRUCTURE OF RHCH2-MECHANISM - RHCH2++H2-]RH++CH4( AND THE REACTION)

By using CASSCF and MR-SDCI-CASSCF methods we have calculated electron ic and geometric structures of RhCH2+, as well as the potential energy surfaces (PESs) of reaction: RhCH2+ + H-2 --> Rh+ + CH4. The ground s tate of RhCH2+ is 1A1, and nearly degenerate 3A1 and 3A2 states lie ab out 4-5 kcal/mol higher. The calculated binding energy for RhCH2+(1A1) --> (Rh+(F))-F-3 + (CH2(B1))-B-3 is 78.3 kcal/mol vs experimental res ults of 91 +/- 5 kcal/mol. The PESs of the reaction, calculated for th e ground 1A1 and the excited 3A1 states of RhCH2+, are very similar. I n the first step, reactants give an ion-molecule complex, (H2)RhCH2+, with a stabilization energy of about 7 kcal/mol. Then the H-H bond act ivation takes place with a 16 kcal/mol barrier. The resultant complex HRhCH3+ probably does not exist but rearranges without barrier to the product complex Rh(CH4+(3A'), which is stable by about 17 kcal/mol rel ative to (Rh+(F))-F-3 + CH4.