速度选择分子束源装置的搭建与应用

反应动力学是一门研究化学反应机理的学科，广泛应用于大气化学、星际化学等领域。其中，量子态分辨的微观反应动力学是前沿的研究方向，而制备态选择分子束源是研究该方向的前提。本文旨在从头搭建一套分子束源装置，详细介绍了相关实验技术与原理，以及真空、光学、信号控制与采集等基础仪器部分的搭建与测试工作。基于这些基础仪器，本文主要研究了速度连续可调超窄脉冲分子束的制备。

本文作者设计了一套结合斩波器制备速度可调超窄脉冲分子束的装置，并通过共振增强多光子电离进行速度表征。通过斩波器与脉冲阀的配合，在束源下游193 mm处得到了半高宽为6.3 μs的超窄H₂脉冲分子束。通过改变脉冲阀温度，实现了束源温度从95 K~503 K连续可调，并通过受激拉曼泵浦标记分子，在纳秒尺度上精确测量了分子束速度，制备了速度分布在1.32 km/s~3.6 km/s的H₂分子束。另外通过混合载气将分子束速度降低至0.83 km/s，实现了速度在0.83 km/s~3.6 km/s可调的超窄H₂分子束源的制备。

为了获得速度更低的分子束，本文设计搭建了一套基于低温缓冲气体冷却技术的束源装置。通过改进导热元件以及低温屏蔽装置，缓冲气体冷却腔室温度可降低至7.4 K。在冷却温度为20 K的缓冲气体冷却腔室中初步制备了低速连续H₂分子束。本文的研究结果为量子态分辨的微观反应动力学研究提供了可靠的实验方法和装置，对于深入理解化学反应机理具有重要意义。

Reaction dynamics investigates the mechanisms of elementary chemical reactions, which is widely used in atmospheric, interstellar chemical and other fields. One advance area of the research is quantum-state-resolved reaction dynamics, which requires the preparation of a state-selected beam source. This thesis focuses on the construction of a molecular beam source and outlines the relevant experimental techniques and principles employed in the field of molecular beams, then introduces a detailed description of the construction and testing of components of the essential apparatus, such as vacuum, optical, signal control and acquisition of this device. The preparation of continuously velocity-tunable and narrowed pulsed molecular beams was mainly implemented based on these basic devices.

A device was developed to prepare velocity-tunable and narrowed pulsed molecular beams in conjunction with a chopper. In this thesis, the beam velocity was characterized by resonance-enhanced multiphoton ionization. By cooperation of the chopper and the pulsed valve, an ultra-narrow H₂ pulsed molecular beam with a full width at half maxima of 6.3 μs at 193 mm downstream from the pulsed valve was obtained. The beam source temperature could be continuously adjusted from 95 K to 503 K by changing the temperature of pulse valve. The molecular beam velocity was precisely measured by excited Raman pumping tagging of molecules on the nanosecond scale. As a result, the H₂ molecular beams with velocity distributions ranging from 1.32 km/s to 3.6 km/s were prepared. Furthermore, the velocity of molecular beam was reduced to 0.83 km/s by loading gas, thereby a velocity-tunable and narrowed H₂ molecular beam source with velocity distributions ranging from 0.83 km/s to 3.6 km/s was obtained.

In order to prepare molecular beam with lower velocity, a beam source utilizing cryogenic buffer gas cooling technology was designed and built. By optimizing the thermal conducting components and the cryogenic shielding components, the buffer gas cooling chamber could be cooled down to 7.4 K. In the buffer gas cooling chamber at a cooling temperature of 20 K, a continuous slowed H₂ molecular beam was obtained. The research results of this thesis provide a reliable experimental method and apparatus for the study of micro-reaction dynamics with quantum-state resolution, which is of great significance for a deeper understanding of chemical reaction mechanisms.

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