Heritier K L, Jaffe R L, Laporta V, Panesi M
Department of Aerospace Engineering, University of Illinois at Urbana-Champaign, 104 S. Wright Street, Urbana, Illinois 61801, USA.
Aerothermodynamics Branch, NASA Ames Research Center, Mail Stop 230-3, Moffett Field, California 94035, USA.
J Chem Phys. 2014 Nov 14;141(18):184302. doi: 10.1063/1.4900508.
The relaxation of N₂(X¹Σg⁺) molecules in a background gas composed of N((4)S(u)) atoms and free electrons is studied by using an ideal isochoric and isothermic chemical reactor. A rovibrational state-to-state model is developed to study energy transfer process induced by free electron and atomic collisions. The required cross sections and the corresponding rate coefficients are taken from two well-known kinetic databases: NASA Ames kinetic mechanism for the description of the N₂(X¹Σg⁺)-N((4)S(u)) processes and the Phys4Entry database for the electron driven processes, N₂(X¹Σg⁺)-e(-). The evolution of the population densities of each individual rovibrational level is explicitly determined via the numerical solution of the master equation for temperatures ranging from 10000 to 30,000 K. It was found that the distribution of the rovibrational energy levels of N₂(X¹Σg⁺) is strongly influenced by the electron driven collisional processes, which promote the excitation of the low lying vibrational levels. The macroscopic vibrational energy relaxation is governed by the molecule-atom collisions, when free electrons, initially cold are relaxing to the final heat-bath temperature. Thus, the main role of the free electrons is to ensure the equilibration of vibrational and free electron excitation, thus validating the existence of the local equilibrium T(V)-T(e). However, if electrons and heavy particles are assumed to be in equilibrium at the heat bath temperature, electron driven processes dominate the vibrational relaxation. Finally, we have assessed the validity of the Landau-Teller model for the description of the inelastic energy transfer between molecules and free electrons. In the case of free-electron temperatures lower than 10,000 K, Landau-Teller relaxation model gives an accurate description of the vibrational relaxation, while at higher temperatures the error in the predictions can be significant and the model should not be used.
利用理想的等容等温化学反应器，研究了在由N((4)S(u))原子和自由电子组成的背景气体中N₂(X¹Σg⁺)分子的弛豫过程。建立了一个振转态到态模型来研究自由电子和原子碰撞引起的能量转移过程。所需的截面和相应的速率系数取自两个著名的动力学数据库：用于描述N₂(X¹Σg⁺)-N((4)S(u))过程的美国国家航空航天局艾姆斯动力学机制，以及用于电子驱动过程N₂(X¹Σg⁺)-e(-)的Phys4Entry数据库。通过对温度范围从10000到30000 K的主方程进行数值求解，明确确定了每个振转能级的粒子数密度的演化。研究发现，N₂(X¹Σg⁺)振转能级的分布受到电子驱动碰撞过程的强烈影响，这些过程促进了低振动态的激发。当最初处于低温的自由电子弛豫到最终热浴温度时，宏观振动能量弛豫由分子-原子碰撞控制。因此，自由电子的主要作用是确保振动和自由电子激发的平衡，从而验证了局部平衡T(V)-T(e)的存在。然而，如果假设电子和重粒子在热浴温度下处于平衡，则电子驱动过程主导振动弛豫。最后，我们评估了朗道-泰勒模型在描述分子与自由电子之间非弹性能量转移方面的有效性。在自由电子温度低于100００ K的情况下，朗道-泰勒弛豫模型能准确描述振动弛豫，而在较高温度下，预测误差可能很大，该模型不应使用。
