On nd bonding in the transition metal trimers: comparison of Sc3 and Y3

CASSCF/CCI calculations are presented for the low-lying states of Y. Comparison of the wave functions for Y and Sc indicates substantial 4-5 hybridization in Y, but little 3-4 hybridization in Sc. The increased 4-5 hybridization leads to stabilization of 4 bonding with respect to 4σ bonding for equilateral triangle Y, and also leads to 4-5 bonding for linear geometries. These effects lead to a different ordering of states for equilateral triangle geometries and a smaller excitation energy to the linear configuration for Y as compared to Sc.