Development of a new model for vibration-dissociation coupling in nitrogen

A new model for vibration-dissociation coupling is derived using knowledge obtained from a simulation of the vibrational relaxation of heated nitrogen by collisional processes. This bi-Ievel model is based on the assumption that nitrogen can be represented by two molecular species. The first species, N₂*, consists of vibrational excited molecules with energies within kT of the dissociation energy. Only these molecules are allowed to dissociate. The second species, N₂, consists of molecules with vibrational energies less than the threshold value. This species is modeled by a truncated harmonic oscillator. The vibrational energy relaxation is represented by a modified form of the Landau-Teller equation. The effects of the bi-Ievel model on a typical hypervelocity flowfield computation are examined and compared to the Park TT_V model. Specifically, it is found that the bilevel model exhibits a decreased dissociation rate. This is believed to be due to the inhibition of dissociation by nonequilibrium vibrational relaxation.