台阶波压缩稠密气体氧在离解相变区的状态方程及光谱研究

Oxygen is the third high abundance element in the universe, its equation of state, spectrum, and thermodynamic properties in the extreme conditions of high temperature and high pressure play an important role in the earth physics, astrophysics, and detonation physics research. As a typical diatomic molecule, oxygen is also the ideal object for establishing and testing the material theoretical models under extreme conditions. However, up to now, there are still controversies about the dissociation phase transition mechanism of diatomic molecules under shock compressions, as well as the influence of dissociation on equation of state and spectrum. In this project, we will focus on the contraversies of dissociation phase transition of diatomic molecules under shock compressions, and choose the precompressed dense gaseous oxygen as the research object, using the two-layer flyer driven by two-stage light gas gun to generate step shock waves, together with the shock reverberation technique and the comprehensive diagnosis technique with multiple measurement methods, to obtain the equation of state and shock radiation spectrum of oxygen in a wide pressure range from dense gas up to 100 GPa, which will provide experimental basis for establishing and testing theoretical models. Moreover, the dissociation phase transition mechanism of diatomic molecules under shock compressions will be clarified through the investigation of equation of state and radiation spectrum of oxygen in the dissociation phase transition regime. Finally, we will build a free energy theoretical model, in which both molecular dissociation and atom ionization are able to be taken into account, to promote the comprehensive physical modeling of matter under extreme conditions.

氧是宇宙中丰度第三高的元素，其在高温高压极端条件下的状态方程、光谱及热力学性质等在地球物理、天体物理和爆轰物理研究中具有重要作用。氧作为典型双原子分子，也是建立和检验极端条件下物质理论模型最理想的对象。然而，目前对双原子分子在冲击压缩下的离解相变机制及其对状态方程、光谱等的影响研究仍存在争议。本项目以预压缩的稠密气体氧为研究对象，针对双原子分子在冲击压缩下的离解相变认识争议，利用二级轻气炮驱动双层阻抗飞片产生台阶波，结合冲击波多次反射压缩实验技术及多种测试手段的同步联合诊断技术，获取氧从稠密气体直到百GPa压力的宽区域状态方程和冲击辐射光谱实验数据，为建立和检验理论模型提供实验依据。通过对氧在离解相变区状态方程及辐射光谱的研究，澄清双原子分子在冲击压缩下的离解相变机制。进而建立能够同时考虑氧在高温高压下分子离解和原子电离反应的自由能理论模型，推动极端条件下物质的综合物理建模研究。

氧是宇宙中丰度第三高的元素，广泛地存在于地球内部、气态巨行星内部、恒星内部以及爆轰产物之中，其在高温高压极端条件下的状态方程、光谱及热力学性质等在地球物理、天体物理和爆轰物理研究中具有重要作用。本项目基于二级轻气炮动态加载平台，通过优化设计满足多次反射压缩条件的多层介质靶装置以及多种诊断手段联合的同步诊断技术，对初始压强为数十MPa的稠密氧气开展了多次反射冲击压缩，获取了氧在5-170 GPa宽压力范围的状态方程实验数据，极大地拓展了现有实验数据的范围。同时，通过对冲击辐射光谱的测量和分析，获取了稠密氧在一次冲击压缩下的温度信息，为6000-14000 K。基于宽区域的状态方程实验数据，对第一性原理分子动力学模拟和化学模型在实验压力范围内的适用性进行了有效地校验和验证，为极端条件下物质的综合物理建模研究提供科学的依据。设计了由304不锈钢和钽两种不同材料组成的双层阻抗飞片，并利用二级轻气炮开展了组合飞片加载下稠密氧气的辐射性质研究。双层阻抗飞片加载产生明显的台阶波，先后对稠密氧气进行两次压缩。通过对稠密氧气在台阶波压缩下的辐射光谱进行测量与分析，发现稠密氧气在二次压缩下冲击温度反常地出现下降。上述多次反射冲击加载及诊断测试技术为稠密气体在极端条件下的性质研究提供了有效的手段，获取的氧宽区域状态方程实验数据为建立和检验理论模型提供了数据支撑。而基于双层阻抗飞片驱动台阶波能够产生偏离Hugoniot状态的热力学路径，为后续开展基于多层飞片产生更加复杂的热力学路径（如准等熵压缩）奠定了研究基础。