Theoretical study of SiH2n2+ (n=1-3) dications

Structures and energies of SiH2n2+ (n = 1-3) dications were calculated at t he density functional theory (DFT) B3LYP/6-311+G(d,p) and B3LYP/6-311++G(3d f,2pd) levels. Contrary to the previously reported theoretical studies at t he HF/6-31G* level, the singlet SiH22+ is not of linear D-infinity h symmet ric 1 but a C-2v, symmetrical 2 with a two electron three center (3c-2e)bon d. The structure 2 is significantly more stable than I by 14.7 kcal/mol. Fo r calibration, structures 1 and 2 were also calculated at the ab initio CCS D(T)/cc-pVTZ level and found results which are in good agreement with the D FT results. DFT calculations also indicate that the singlet SiH42+ is not o f C-2v symmetric 4 with a 3c-2e bond but a C-2v symmetric 5 with two 3c-2e bonds. The C-2v symmetric 7 with two 3c-2e bonds and two 2c-2e bonds was fo und to be the global minimum for SiH62+ dications.