The ground states of Si3H and Si3H- have been found as (2)A(1) (C-2v)
and (1)A(1) (C-2v), respectively, and both correspond to planar cyclic
hydrogen-bridged geometries. The adiabatic electron affinity is calcu
lated as 256 kJ/mol at the CCSD-(T) level of theory. The in-plane flux
ionality of the neutral radical is much more pronounced than that of t
he negative ion. Besides these two minima, various stationary points (
minima as well as transition states) for the neutral as well as the ne
gative ion have been located. Several triplet negative ion states are
found to be adiabatically stable.