The vibrational energy relaxation in collisions between N2 molecules in the low- and medium-lying vibrationally excited levels was revisited using the semiclassical coupled-state method and the use of two different potential-energy surfaces having the same short-range potential recently determined from ab initio calculations but with different long-range interactions. Compared to the data reported in the classical work by Billing and Fisher [Chem. Phys. 43, 395 (1979)], the newly calculated vibration-to-translation rate constant K(1,0 / 0,0) is in much better agreement with the available experimental data over a large temperature interval, from T = 200 K up to T = 6000 K. Nevertheless, as far as the vibration-to-translation exchanges are concerned, the lower-temperature regime remains quite critical in that the new rate constants do not completely account for the rate constant curvature suggested by the experiments for temperatures lower than T = 500 K. The dependence of the state-selected vibration-to-vibration rate constants, K(v,v-delta v / 0,1), both upon the vibrational quantum number v and the gas temperature are calculated. The substantial deviations from previously found behaviors could have major consequences for the vibrational kinetic modeling of N2-containing gas mixtures.

By following the scheme of the Grid Empowered Molecular Simulator (GEMS), a new O2 + N2 intermolecular potential, built on ab initio calculations and experimental (scattering and second virial coefficient) data, has been coupled with an appropriate intramolecular one. On the resulting potential energy surface detailed rate coefficients for collision induced vibrational energy exchanges have been computed using a semiclassical method. A cross comparison of the computed rate coefficients with the outcomes of previous semiclassical calculations and kinetic experiments has provided a foundation for characterizing the main features of the vibrational energy transfer processes of the title system as well as a critical reading of the trajectory outcomes and kinetic data. On the implemented procedures massive trajectory runs for the proper interval of initial conditions have singled out structures of the vibrational distributions useful to formulate scaling relationships for complex molecular simulations.

The state-to-state collisional data on vibration-vibration and vibration-translation/rotation energy exchanged in N2(v)-N2(v') collisions recently obtained from accurate ab initio semiclassical calculations have been used to analyze the data measured in nitrogen under two different plasma conditions. In particular, the vibrational distribution function and the time-evolution of the gas temperature measured under post-discharge and glow discharge conditions, respectively, have been calculated and compared with the experimental observations. The theoretical analysis and the related results, generally in very good agreement with the experimental data, provide insight into the various energy-exchange mechanisms that lie behind the macroscopic behaviors of the nitrogen plasmas. In particular, the role played by the vibrationally excited nitrogen molecules in the gas kinetics is pointed out, as well as the importance of nitrogen atom production in the long time scales of the glow discharge.

Extensive semiclassical calculations have been performed regarding the generation of accurate collision data for single-and multi-quantum vibrational state-selected V-V exchanges in N 2 (v)-N 2 (u) and N 2 (v)-CO(u) collisions over a wide range of vibrational quantum numbers (v, u) and gas temperatures. This highly accurate database is also used to test the applicability of simplified analytical approximations frequently used in vibrational kinetic modeling to calculate large sets of state-to-state V-V rate constants in diatom-diatom collisions. The semiclassical calculations clearly show that the long-range attractive branch of the interaction potential cannot be neglected, even for the N 2 -N 2 system. Therefore, new analytical approximations for V-V exchanges for the two collision systems are proposed which agree very well with the semiclassical rates. The ab initio data, together with that obtained from the newly proposed analytical formula, constitute an accurate database that can be used with confidence in the vibrational kinetic modeling of N 2 and CO-based gases and plasmas over a wide temperature range, from thermal to hyper-thermal gas temperatures.