Ab Initio Study of Reactions of sym-Triazine.
Abstract
Ab initio calculations were performed to investigate reaction mechanisms for formation and decomposition of the six-membered ring C3N3H3, known as sym-triazine. MP2 geometry optimizations with QCISD(T) energy refinements for critical points on the potential energy surface were calculated with the 6-31G**, 6-311++G**, and cc-pVTZ basis sets. Good agreement is found for MP2 geometries and frequencies of sym-triazine and HCN when compared with the corresponding experimental values. Two decomposition mechanisms of sym-triazine, the concerted triple dissociation (sym-triazine right arrow 3 HCN) and the step-wise decomposition (sym-triazine right arrow H2C2N2 + HCN right arrow 3 HCN) were investigated. All calculations show that the lowest-energy decomposition mechanism is the concerted triple dissociation. Our best calculations predict the zero-point-energy-corrected barrier to decomposition to be 81.2 kcal/mol. The calculated reaction enthalpy is 35.5 kcal/mol, 7.7 kcal/mol lower than experiment. Intrinsic reaction coordinate (IRC) calculations leading from the transition state of the concerted triple dissociation reaction to three HCN molecules led to a minimum on the potential energy surface. The corresponding structure is a cyclic (HCN)3 cluster. The temperature-corrected formation enthalpy of the cluster is -8.7 kcal/mol relative to three isolated HCN molecules. The zero-point-corrected barrier to formation of sym-triazine from the cluster is 58.1 kcal/mol. QCISD(T) energy refinements did not differ significantly from the MP2 results.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 1996
- Accession Number
- ADA311238
Entities
People
- Betsy M. Rice
- Cary F. Chabalowski
- Sharmila V. Pai
Organizations
- United States Army Research Laboratory