Molecular simulation of Rayleigh-Brillouin scattering in binary gas mixtures and extraction of the rotational relaxation numbers,Physical Review E

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Molecular simulation of Rayleigh-Brillouin scattering in binary gas mixtures and extraction of the rotational relaxation numbers
Physical Review E ( IF 2.2 ) Pub Date : 2021-09-27 , DOI: 10.1103/physreve.104.035109
Qihan Ma ₁ , Chunxin Yang ₁ , Domenico Bruno ₂ , Jun Zhang ₁

Affiliation

Rayleigh-Brillouin scattering (RBS) in gases has received considerable attention due to its applications in LIDAR (light detection and ranging) remote sensing and gas property measurements. In most cases, the RBS spectra in the kinetic regime are calculated based on kinetic model equations, which are difficult to be applied to complex gas mixtures. In this work, we employ two widely used molecular simulation methods, i.e., direct simulation Monte Carlo (DSMC) and molecular dynamics (MD), to calculate the spontaneous RBS spectra of binary gas mixtures. We validate these two methods by comparing the simulation results for mixtures of argon and helium with the experimental results. Then we extend the RBS calculations to gas mixtures involving polyatomic gases. The rotational relaxation numbers specific to each species pair in DSMC are determined by fitting the DSMC spectra to the MD spectra. Our results show that all the rotational relaxation numbers for air composed of

N_{2}

and

O_{2}

increase with temperature in the range of 300–750 K. We further calculate the RBS spectra for binary mixtures composed of

N_{2}

and one noble monatomic gas, and the simulation results show that the rotational relaxation of

N_{2}

is greatly affected by the mass of the noble gas atoms. This work demonstrates that RBS is a promising and alternative way to study the rotational relaxation process in gas mixtures.

中文翻译：

二元气体混合物中瑞利-布里渊散射的分子模拟和旋转弛豫数的提取

由于其在激光雷达（光探测和测距）遥感和气体性质测量中的应用，气体中的瑞利-布里渊散射 (RBS) 受到了相当多的关注。在大多数情况下，动力学状态下的 RBS 谱是基于动力学模型方程计算的，难以应用于复杂的气体混合物。在这项工作中，我们采用两种广泛使用的分子模拟方法，即直接模拟蒙特卡罗 (DSMC) 和分子动力学 (MD)，来计算二元气体混合物的自发 RBS 光谱。我们通过比较氩氦混合气的模拟结果与实验结果来验证这两种方法。然后我们将 RBS 计算扩展到涉及多原子气体的气体混合物。DSMC 中每个物种对特有的旋转弛豫数是通过将 DSMC 光谱拟合到 MD 光谱来确定的。我们的结果表明，空气的所有旋转弛豫数由