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 (SNSi)-S-2 and cyclic (SPSi)-S-2. The other two isomers are predicted to be similar to 20 to 50 kcal/mol less stable than the ground state. The excess spin is mainly on S for (SNSi)-S-2 and on P for (SPSi)-S-2. The calculated total atomization energies with the CBS limits derived from different methods differ by similar to 2 kcal/mol. The results provide the best available heats of formation for these species. The bond dissociation energies (BDEs) in (SNSi)-S-2 are comparable to those in the corresponding diatomic molecules. For cyclic (SPSi)-S-2, the formation of P-4 + (SSi)-S-2 requires less energy than the other bond dissociation processes. The BDEs in the higher energy isomers are substantially smaller than the corresponding diatomic species.