The influence of experimental conditions on absolute beam density measurements for NH\(_3\) and H

IF 1.5 4区 物理与天体物理 Q3 OPTICS The European Physical Journal D Pub Date : 2024-08-20 DOI:10.1140/epjd/s10053-024-00899-3
Rahul Pandey, Lok Yiu Wu, Lucy Morris, Paul Regan, Brianna R. Heazlewood
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Abstract

In order to establish important reaction properties, such as rate coefficients, it is often necessary to know the number of reactants that are present in an interaction region. The absolute number densities of pulsed supersonic molecular (NH\(_3\)) and atomic (H) beams are reported using a laser-based detection method, under a range of experimental conditions including photolysis, Zeeman deceleration, and magnetic focusing. Time-averaged densities of (3.6 ± 2.7) \(\times \) 10\(^4\) cm\(^{-3}\) are reported for successfully Zeeman-decelerated and magnetically focused H atoms, generated by the photodissociation of precursor NH\(_3\) molecules. Without the magnetic guide components in the beamline, the density of the target radicals of interest is somewhat lower, at (2.5 ± 1.8) \(\times \) 10\(^4\) cm\(^{-3}\). The average density of the undecelerated H atom beam is approximately an order of magnitude higher (2.9 ± 1.9) \(\times \) 10\(^5\) cm\(^{-3}\), with the average density of the molecular ammonia beam over two orders of magnitude higher again (5.1 ± 2.9) \(\times \) 10\(^7\) cm\(^{-3}\). The average number densities measured for the two different species of interest in this work span more than three orders of magnitude. These findings highlight the need for accurate and precise experimental measurements of number densities—for each species of interest, under the appropriate experimental conditions—before doing absolute rate coefficient calculations.

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实验条件对 NH $_$3$ 和 H 绝对束密度测定的影响
摘要为了确定重要的反应特性,如速率系数,通常需要知道存在于相互作用区域的反应物的数量。在一系列实验条件(包括光解、泽曼减速和磁聚焦)下,采用基于激光的探测方法,报告了脉冲超音速分子(NH)和原子(H)束的绝对数量密度。报告了成功的泽曼减速和磁聚焦H原子的时间平均密度为(3.6 ± 2.7) \(\times \) 10\(^4\) cm\(^{-3}\) ,这些H原子是由前体NH(_3)分子的光解离产生的。如果光束线中没有导磁元件,目标自由基的密度会更低一些,为(2.5 ± 1.8) 10(^4) cm(^{-3})。未减速的 H 原子光束的平均密度大约高出一个数量级(2.9 ± 1.9 ) 10 (^5) cm\ (^{-3}\ ),分子氨光束的平均密度又高出两个数量级(5.1 ± 2.9 ) 10 (^7) cm\ (^{-3}\ )。在这项工作中,针对两种不同物种测得的平均数量密度跨越了三个数量级。这些发现突出表明,在进行绝对速率系数计算之前,需要在适当的实验条件下对每种相关物质的数量密度进行准确和精确的实验测量。
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来源期刊
The European Physical Journal D
The European Physical Journal D 物理-物理:原子、分子和化学物理
CiteScore
3.10
自引率
11.10%
发文量
213
审稿时长
3 months
期刊介绍: The European Physical Journal D (EPJ D) presents new and original research results in: Atomic Physics; Molecular Physics and Chemical Physics; Atomic and Molecular Collisions; Clusters and Nanostructures; Plasma Physics; Laser Cooling and Quantum Gas; Nonlinear Dynamics; Optical Physics; Quantum Optics and Quantum Information; Ultraintense and Ultrashort Laser Fields. The range of topics covered in these areas is extensive, from Molecular Interaction and Reactivity to Spectroscopy and Thermodynamics of Clusters, from Atomic Optics to Bose-Einstein Condensation to Femtochemistry.
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