Structures, relative stability and dissociation of [Si,N,C,O]2+ isomers

Fifteen isomers of [Si,N,C,O](2+) system are obtained at UB3LYP/6-311G(d) and, UCCSD(T)/6-311+G(2df) (single-point) levels. The analyses are made for predicting the structures of optimized isomers, while ionic fragments with lower energies are suggested. The calculated results indicate that linear isomer SiNCO2+((2)Pi) is thermodynamically the most stable species in [Si,N,C,O](2+) system, followed by linear SiOCN2+((2)Pi), SiCNO2+((2)Pi), and SiC(NO) ((2)A") with NCO three-membered ring. The order of stability of several kinetically stable isomers is SiNCO2 > SiCNO2+((2)Pi) > SiOCN2+ > SiC(NO)(2+) > OSiNC2+ ((2)Pi). The obtained results by analyzing the isomerizations and ionic fragment patterns show that the signal peaks of [Si,N,C,O](2+) are attributed to the contribution of linear SiNCO2+ species, which is metastable and can dissociate to the ionic fragments in the mass spectrometry experiments.