First-Principle Calculations of Collision Integrals for N_2-O System

摘要

Collision integrals related to viscosity and coefficient of diffusion are calculated by quasi-classical trajectory (QCT) method for N_2-O system. Three ab-initio potential energy surfaces (PES) for 1~1A', 1~3A' and 1~3A" electronic states are used. Contributions of inelastic collisions to collision integrals are taken into account by Wang-Chang and Uhlenbeck's theory. The results show that, collision integrals change by up to 20% for the two triplet states and 50% for the singlet state at vibrational nonequilibrium conditions. For conditions with |T - T_v| ≤ 5,000 K, the deviation of collisions integrals from their value at thermal equilibrium conditions is less than 5% and collision integrals, as well as transport coefficients, can be described by a single translational temperature. Compared with those obtained by using Lennard-Jones and exponential potential, the new results are within the uncertainty interval. By studying scattering angles, strong forward scattering is found at hyperthermal conditions, which implies that isotropic scattering law tends to overpredict transport properties. Phenomenological models like variable hard sphere (VHS) in direct simulation Monte Carlo (DSMC) become inaccurate for hyperthermal collisions. A new collision model is suggested based on the QCT results.