Laboratory measurements on cold electron reactions with key species of interstellar chemistry using ion beams

在星际介质的化学网络中，涉及带电粒子(原子离子、多原子分子离子和电子)的二元反应是在远低于标准实验室条件的温度和密度下的关键驱动机制。为了获得和改进这种过程的实验室数据，人们提出了用储存的离子束进行逐个事件的反应研究，特别是关于离子和电子之间的低能复合反应。通过将单个反应产物的计数和多粒子碎裂成像与冷光电阴极电子束的使用相结合，在最近的工作中成功地实现了这类研究。然而，对于冷离子化学过程，由于室温热辐射和太短的束流存储寿命，它们受到了限制。因此，建议在低温静电储存环CSR上实施这项技术，这将为通过离子束低温冷却环境研究冷离子化学过程提供更有利的条件和更长的储存寿命。将获得多原子分子离子与冷电子在大大减少的初始旋转激发下的解离复合(不受室温热辐射影响)的数据，以及较重的单电荷原子离子的双电子复合的数据，这些离子形成的高激发里德堡原子的灵敏度大大提高。该项目使CSR成为研究星际介质中离子化学的独特实验室。

In the chemical network of the interstellar medium binary reactions involving charged particles (atomic ions, polyatomic molecular ions and electrons) are crucial driving mechanisms at temperatures and densities much below standard laboratory conditions. In order to obtain and improve laboratory data on such processes, event-by-event reaction studies with stored ion beams are proposed on low-energy recombination reactions between ions and electrons in particular. By combining the counting of individual reaction products and the imaging of multiparticle fragmentation with the use of cold photocathode electron beams, such studies have been successfully realized in recent work. For cold ion chemistry processes, however, they hit limitations due to the room-temperature thermal radiation and too short beam storage lifetimes. It is hence proposed to implement the technique at the cryogenic electrostatic storage ring CSR, which will offer much more favorable conditions for the study of processes in cold ion chemistry through the cryogenically cooled surrounding of the ion beam and much longer storage lifetimes. Data will be obtained for dissociative recombination of polyatomic molecular ions with cold electrons at much reduced initial rotational excitation, unaffected by room-temperature thermal radiation, and for dielectronic recombination of heavier singly charged atomic ions with a strongly improved sensitivity for the highly excited Rydberg atoms formed. The project opens up CSR as a unique laboratory for the study of ion chemistry in the interstellar medium.