THE C4H4-CENTER-DOT-ENERGY SURFACE .2. THE JAHN-TELLER STABILIZATION OF IONIZED TETRAHEDRANE AND ITS REARRANGEMENT TO CYCLOBUTADIENE RADICAL-CATION( POTENTIAL)

The Jahn-Teller potential energy surface of the radical cation of tetr ahedrane is explored by quantum chemical calculations and modeled anal ytically. The first- and second-order vibronic constants are evaluated . The rearrangement to the cyclobutadiene radical cation, which was pr eviously predicted to occur with no activation, is investigated by the same quantum chemical method (CCSD (T)/cc-pVTZ//QCISD/6-31G). It is shown that the localization of the HOMO which is necessary for adiabat ic crossover requires some energy, which leads to a 0 K activation bar rier of 4.3 kcal/mol for the process. It is concluded that the radical cations of substituted tetrahedranes should persist at low temperatur es if they can be formed with little excess energy.