Accession Number : ADA311238

Title :   Ab Initio Study of Reactions of sym-Triazine.

Descriptive Note : Final rept. Mar-Aug 94,

Corporate Author : ARMY RESEARCH LAB ABERDEEN PROVING GROUND MD

Personal Author(s) : Pai, Sharmila V. ; Chabalowski, Cary F. ; Rice, Betsy M.

PDF Url : ADA311238

Report Date : JUN 1996

Pagination or Media Count : 48

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.

Descriptors :   *CHEMICAL REACTIONS, *TRIAZINES, COMPUTATIONS, QUANTUM CHEMISTRY, MOLECULES, SURFACES, TRANSITIONS, POTENTIAL ENERGY, DISSOCIATION, DECOMPOSITION, ENTHALPY.

Subject Categories : Organic Chemistry
      Physical Chemistry
      Atomic and Molecular Physics and Spectroscopy
      Quantum Theory and Relativity
      Thermodynamics

Distribution Statement : APPROVED FOR PUBLIC RELEASE