超低温(uK-mK)离子+原子+原子三体复合的全维量子力学理论研究

Traditional studies of molecular reaction dynamics mainly focused on the two-body scatterings, such as A+BC->AB+C, while less attention was paid to the three-body recombination. The latter is a three-body collision in which two atoms form a dimer molecule and the third one carries away the binding energy, X+Y+Z->XY+Z. Three-body recombination of ion+atom+atom in ultracold (uK-mK) conditions, is one of the most important processes in ultracold chemistry and interstellar chemistry, of which the relevant reaction mechanisms still need to be deeply understood. In addition, limited by the factors, such as the huge reaction distance (over tens of thousands of Bohr) and the imperfection of the basis function for the three-body continuum state, the transitional A+BC two-body scattering theory, which is well programmed, is unable to solve this type of problems. Stimulated by this, in this project, we will perform full-dimensional quantum mechanics study of the hydrogen anion+helium+helium and the isotopic substitution systems by solving the time-independent Schrodinger equation with the adiabatic hyperspherical representation method. By taking into account of the multi-channel coupling effects and the cases of total angular momentum J>0, we will calculate the scattering wave functions, the reaction cross section, and the rate constant, etc. The variation of the recombination rates of the neutral molecular and the molecular ion channels with the temperature as well as the competition mechanisms will be investigated. By comparing the isotopic substitution systems, we will further investigate several quantum effects, including the nonadiabatic coupling and the resonant quantum states, etc. By performing this investigation, it is expected to promote our understanding of the ultracold chemistry and to complete the quantum scattering theory.

传统分子反应动力学研究多关注两体散射如A+BC->AB+C，而对三体复合反应关注较少。后者是三个粒子碰撞形成二聚物分子并由第三个粒子带走结合能的过程，X+Y+Z->XY+Z。超低温uK-mK条件下离子+原子+原子的三体复合，是超低温化学和星际化学的重要过程，相关反应机理有待深入认识；但受限于万波尔量级的超大反应距离和基函数对三体连续态描述的不完备性等因素，传统程序化的A+BC两体散射理论无法求解此类问题。为此，项目拟以氢负离子+氦+氦及其同位素组成的三体系统为例，发展绝热超球表象方法求解非含时薛定谔方程，开展全维量子力学研究。考虑多通道耦合效应和总角动量大于零等情况，计算体系波函数、反应截面、速率常数等，分析中性分子和分子离子通道复合速率随温度的变化趋势和竞争机制；对比同位素取代体系，考察非绝热耦合、共振态等量子效应的影响。期望通过本项目研究，推动对超低温化学反应的认识并完善量子散射理论。

传统分子反应动力学研究多关注两体散射如A+BC-->AB+C，而对三体复合反应（A+B+C-->AB+C）关注较少。超低温uK-mK条件下离子+原子+原子的三体复合，是超冷化学的主导反应类型，也是超低温化学和星际化学的重要过程，相关反应机理有待深入认识。受限于万波尔量级的超大反应距离和基函数对三体连续态描述的不完备性等因素，传统的A+BC两体散射理论无法求解此类问题。本项目以“绝热超球表象”方法为基础，建立了描述离子+原子+原子体系超低温三体复合的全维量子力学理论模型。推导了绝热超球表象的基函数（通道函数，channel function）的本征方程，构建了描述通道之间相互作用的耦合方程组。在考虑体系的对称性以及相应边界条件的前提下，完成了相关方程数值求解程序的编写、测试和优化。基于该理论和计算程序，对 3He + 3He + [X]和4He + 4He + [X], X = H-, D-, T-, 20Ne, 9Be, 24Mg, 40Ca, 88Sr, 138Ba等体系的超低温三体复合过程进行了详细研究。精确给出了相关体系三体复合速率和碰撞诱导解离速率等重要参考数据随碰撞能量变化的函数图像。比较了各个分波对相应产物通道散射波函数、反应截面以及复合速率（或解离速率）的贡献度，分析了各离子产物通道复合速率随碰撞变化的原因及通道间的竞争机制。进一步在主导分波各通道的势函数和相互间非绝热耦合函数图像下，提出了选择性开放通道的理论模型，深入分析了各通道对反应速率的贡献，解释了各体系的反应机理。此外，针对超低温三体碰撞相关的势函数构建、能量转移、超冷两体散射、激光诱导两体光缔合、光解离等问题也开展了研究。包括构建He2H-、He3、Li2等体系高精度势函数、揭示H + C2Hx --> H2 + C2Hx-1等体系“碰撞漫游反应机理”、阐明H + C2Hx体系超级能量转移机理、解释6Li2体系磁诱导Feshbach共振现象的温度依赖性、发展全维随机相位波包方法模拟Mg2高能光缔合等。相关研究结果为揭示超冷三体散射的动力学本质提供了理论和数据支撑。

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