Energetic Properties and Electronic Structure of [Si,N,S] and [Si,P,S] Isomers

Correlated molecular orbital theory at the coupled cluster CCSD­(T) level with augmented correlation consistent basis sets has been used to predict the structure and energetic properties of the isomers of [Si,N,S] and [Si,P,S]. The predicted ground states are linear ²SNSi and cyclic ²SPSi. The other two isomers are predicted to be ∼20 to 50 kcal/mol less stable than the ground state. The excess spin is mainly on S for ²SNSi and on P for ²SPSi. The calculated total atomization energies with the CBS limits derived from different methods differ by ∼2 kcal/mol. The results provide the best available heats of formation for these species. The bond dissociation energies (BDEs) in ²SNSi are comparable to those in the corresponding diatomic molecules. For cyclic ²SPSi, the formation of ⁴P + ²SSi requires less energy than the other bond dissociation processes. The BDEs in the higher energy isomers are substantially smaller than the corresponding diatomic species