DIAZASILENE (SINN) - A COMPARISON OF COUPLED CLUSTER-METHODS WITH EXPERIMENT AND LOCAL DENSITY FUNCTIONAL METHODS

Ab initio quantum mechanical methods have been applied to the 3-SIGMA-electronic ground state of the diazasilene molecule SiNN. Higher level electron correlation methods are found to significantly effect the predicted equilibrium geometry. The self-consistent-field (SCF) and single and double excitation configuration interaction (CISD) methods predict a loosely bound Si...N=N structure. The single and double excitation coupled cluster method (CCSD) predicts both the loose structure and a tightly bound Si-N2 Structure, with the latter lying 2.3 kcal/mol lower in energy. The highest level theoretical method, CCSD(T), includes all connected triple excitations and predicts only the tight Si-N2 Structure. The CCSD(T) vibrational frequencies are in close agreement with experiment and in qualitative agreement with local density functional methods.