Study of the CN(X2Σ+) + N(4S) Reaction at High Temperatures: Potential Energy Surface and Thermal Rate Coefficients.

Reactions involving C and N play an essential role in the chemistry around the surface of a hypersonic spacecraft during its atmospheric re-entry. The collision of CN with other molecules and atoms has particular interest in aerothermodynamic modeling. This work focuses on the study of the CN + N → N2 + C reaction in the triplet manifold 3A″ of CN2. A high-level full-dimensional potential energy surface for this system is developed from ab initio calculations at the MRCI-F12 + Q level of theory. This surface is employed in quasiclassical trajectory calculations, and thermal rate coefficients from 100 to 20,000 K are computed. The rates for the formation of N2 are compared with the available experimental data, and good agreement is found. At low and intermediate temperatures, the N2 formation is more efficient than the N-exchange process, while at high temperatures, the rates for both processes are comparable. Finally, analytically modified Arrhenius expressions for the reaction rates of N2 formation and N-exchange are reported.