Relativistic calculations of electronic states and potential energy surfaces of Sn3

Abstract

Complete active space MCSCF (CASSCF) followed by multireference singles and doubles CI (MRSDCI) calculations are carried out on the low-lying electronic states of Sn3. Relativistic effective core potentials with the outer d10s2p2 shell as the valence shell are employed for the tin atom. Calculations of a number of electronic states of both equilateral and isoceles triangular structures reveal the existence of two nearly degenerate structures. The ground state of Sn3 is found to be the 1A1 state (isosceles triangle) with re=2.723 Å and an apex angle of 83°. The 3A′2 state arising from the equilateral triangular structure is about 4 kcal/mol above the 1A1 state in the absence of spin-orbit interaction. The properties of the low-lying electronic states of Sn3 are compared with Si3. The bending potential energy surfaces of the 1A1 and 3B2 states are calculated. It is predicted that the potential energy surface of the ground state of Sn3 (A1) in the presence of spin-orbit interaction would contain a double minima separated by a small barrier. Thus it is predicted that the Sn3 cluster would be floppy at room temperature. The atomization energy of the ground state is estimated to be about 71 kcal/mol without spin-orbit interaction and 48 kcal/mol in the presence of spin-orbit interaction. The Sn3 cluster is found to be slightly more stable than Sn2.