Investigation of the condensation and freezing behavior of freely suspended supercooled molecular gases and particles in the nano to millimeter size range

在本项目中，将研究过冷分子以及纳米、微米和毫米液滴在气体附近的冷凝、聚集和冻结行为。为此，将采用高分辨率红外光谱、拉曼光谱、太赫兹光谱（利用同步加速器源）和高速拍摄等光学方法。理论支持将特别由合作者通过计算机模拟提供。从我们的小组中，将使用有限元方法来研究冻结过程中的热量产生和分布，以及用于光学粒子表征的离散偶极子近似方法。一个主要的焦点将是一个新的，改进的碰撞冷却系统，该系统将被开发用于冷却，过冷却和光谱分子气体，纳米和微气溶胶在4至400 K的温度区域。对于这一系统，我们将考虑过去15年来在旧的经过良好试验的系统中的经验以及其他技术改进。作为一项关键技术，需要建立更强大的气体过冷进样系统。执行过冷气体的高分辨率光谱，我们的目标是通过全局势超表面提高对分子内动力学的理解。应向HITRAN或GEISHA等数据库提供高质量的测量数据，以考虑在环境科学等方面的应用。关于气溶胶，水和其他物质是重点，因为它们对地球和其他行星及其卫星大气的物理化学以及星际气体都很重要。特别是气溶胶云中微滴的冻结行为（涉及动力学、大小、形状、相和结构演变、热产生和输运、光学常数）；最后但并非最不重要的是对拉曼激光雷达数据的解释。对于毫米大小范围内的水和水溶液中自由悬浮的液滴，应研究和表征以毫秒为单位的第一个快速冻结阶段以及进化的枝状网络冰。在第一个项目阶段，我们观察到一种电效应，显示高达6 V的冻结电位。这种影响现在将被解除。需要解释树枝状冰的不对称网络结构对最终冰内离子分布的影响，特别是对雷云中粒子化学和电势产生的影响。此外，我们将研究规则树枝状冰的形成与空气中雪花的形成的类比，以及向微米尺寸范围内更小颗粒的过渡。

In the project supercooled molecules as well as nano, micro and millimeter droplets shall be investigated with respect to their condensation, aggregation and freezing behavior in a gaseous vicinity. For this purpose, optical methods as high resolution infrared spectroscopy, Raman spectroscopy, terahertz spectroscopy (by use of synchrotron sources), and high-speed filming will be applied. Theoretical support will especially be delivered by collaborators through computer simulations. From our group finite element methods for the investigation of heat production and distribution during freezing as well as the discrete dipole approximation method for optical particle characterization will be used. One main focus will be a new, improved collisional cooling system which shall be developed for cooling, supercooling and spectroscopy of molecular gases, nano and micro aerosols in the temperature region of 4 to 400 K. For this system our experiences of the last 15 years with the old well-tried system will be considered as well as other technical improvements. As a key technology a more powerful sample-gas inlet system for supercooling of gases shall be constructed. Performing high resolution spectroscopy of supercooled gases we aim at an improved understanding of the intra-molecular dynamics via global potential hyper-surfaces. Highly qualitative measuring data shall be delivered for data bases as HITRAN or GEISHA under consideration of applications, e.g., in environmental sciences. Concerning aerosols, water and other substances stand in the focus as they are important for the physical chemistry of the atmospheres of the Earth and other planets and their satellites and also for interstellar gases. Especially the freezing behavior of microdroplets within an aerosol cloud shall be unraveled (concerning dynamics, size-, shape-, phase-, and structure-evolution, heat production and transport, optical constants); last but not least for the interpretation of Raman lidar data. Concerning freely suspended droplets from water and aqueous solutions in the millimeter size range, the first rapid freezing stage which passes in milliseconds shall be investigated and characterized as well as the evolving dendritic network ice. During the first project stage we observed an electric effect showing freezing potentials of up to 6 V. This effect shall be unraveled now. The influence of the asymmetric network structure of the dendritic ice on the ion distribution within the final ice shall be explained, especially the impact on the particle chemistry and electric potential generation in thunderclouds. Furthermore, we will study the analogy of the formation of regular dendritic ice to the formation of snowflakes in air, as well as the transition towards smaller particles in the micrometer size range.