Formation of Polyatomic Molecules at Low Energies: Three-Body Recombination, Radiative Association, and Photoassociation

三体复合（英语：Three-body recombination，TBR）是三个粒子（例如三个原子或小分子）同时碰撞并在其中两个粒子之间形成化学键（二聚体形成）的过程。在这个过程中，第三个粒子离开二聚体，带走了键形成释放的额外能量。这一过程在室温下的化学反应、等离子体环境（如热核聚变反应堆中的等离子体）和接近量子简并度的超冷气体（例如，在高精度计量中使用超冷气体）中具有根本的重要性。尽管它在物理学的几个分支中很重要，但对这个过程的精确理论描述一直很困难。在本项目中，将开发和测试用于快速计算TBR速率常数的理论方法。速率常数是化学反应的关键特征：它们取决于反应物种和温度。此外，在天体物理学，等离子体物理学和化学物理学中，几个基本的三体过程的实际利益（科学和技术）将被考虑。 即类氢原子的三体复合：H + H + H-H2 + H，K + K + K-K2 + K，Rb + Rb + Rb-Rb2 + Rb;激光辅助的A + A + A+光子-A3，或A2 + A+光子-（三聚体光缔合）过程。最后，还将考虑与天体物理学有关的低温下三原子分子的辐射缔合（RA）的相关问题。更确切地说，将研究H-离子与星际空间中最丰富的双原子分子H2和CO的缔合。这一部分的项目可能有助于发现星际空间中的氢离子.氢离子在冷等离子体（如星际介质或热核反应堆的冷区域）中的过程中起着重要作用。成功完成本项目概述的研究将产生几个更广泛的影响：（1）开发的方法和考虑的问题（物理学，化学，天体物理学，等离子体物理学）的跨学科重要性。(2)我们认真对待的一个影响是培养有才华的研究生，他们拥有解决这一学科领域最先进问题所需的工具。(3)本项目的主要研究员正在参加国际原子能机构的协调研究项目：聚变等离子体中氢和氦及其同位素的状态分辨建模原子和分子数据。CRP的目的是提供ITER热核反应堆中发生的化学反应的关键特征，该反应堆目前正在由七名国际参与者组成的团队建造。ITER是一个实验反应堆，旨在证明聚变是未来的能源。

Three-body recombination (TBR) is the process when three particles (for example, three atoms or small molecules) collide simultaneously and form a chemical bond between two of them (dimer formation). During the process, the third particle leaves the dimer carrying away the extra energy released from the bond formation. This process is of a fundamental importance in chemical reactions at room temperature, in plasma environment (such as plasma in thermonuclear fusion reactors), and in ultra-cold gases near the quantum degeneracy (ultra-cold gases are used, for example, in high-precision metrology). Despite its importance in several branches of physics, an accurate theoretical description of the process has been difficult. In the present project a theoretical method for a quick calculation of the TBR rate constants will be developed and tested. The rate constants are the key characteristics for chemical reactions: They depend on the reacting species and the temperature. In addition, several elementary three-body processes of practical interest (in science and technology) in astrophysics, plasma physics, and chemical physics will be considered. Namely, the three-body recombination of hydrogen-like atoms: H+H+H-H2+H, K+K+K-K2+K, and Rb+Rb+Rb-Rb2+Rb; the laser-assisted processes of the type A+A+A+photon-A3, or A2+A+photon-(trimer photoassociation). Finally, a related problem of radiative association (RA) of tri-atomic molecules at low temperatures relevant to astrophysics will also be considered. More precisely, the association of the H- ion with the most abundant diatomic molecules in the interstellar space, H2 and CO, will be studied. This part of the project may help to discover the H- ion in the interstellar space. The the H- ion plays an important role in processes in cold plasma (such as the interstellar medium or cold regions of thermonuclear reactors). Several broader impacts will emerge from the successful completion of the research outlined in this project: (1) Cross-discipline importance of the developed methods and considered problems (physics, chemistry, astrophysics, plasma physics). (2) An impact that we take seriously is the training of talented graduate students who have the tools needed to tackle state-of-the-art problems in this subject area. (3) The principal investigator of the present project is participating in the Coordinated Research Project (CRP) Atomic and Molecular DATA for State-Resolved Modeling of Hydrogen and Helium and their Isotopes in Fusion Plasma of the International Atomic Energy Agency. The purpose of the CRP is to provide the key characteristics of chemical reactions occurring in the ITER thermonuclear reactor that is currently being build by a team of seven international participants. ITER is an experimental reactor aiming to demonstrate that fusion is the energy source of the future.