飞秒激光烧蚀等离子体中分子形成化学的激光烧蚀分子同位素光谱法,Analytical Chemistry

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飞秒激光烧蚀等离子体中分子形成化学的激光烧蚀分子同位素光谱法
Analytical Chemistry ( IF 6.7 ) Pub Date : 2017-07-07 00:00:00 , DOI: 10.1021/acs.analchem.7b01750
Huaming Hou _{1,

2} , Xianglei Mao ₂ , Vassilia Zorba ₂ , Richard E. Russo _{2,

3}

Affiliation

最近，激光烧蚀分子同位素光谱法（LAMIS）扩展了其能力，除了同位素分析之外，还探索了激光诱导等离子体中的分子形成机理。LAMIS是一种强大的工具，可通过用原子的同位素取代标记原子来跟踪参与被调查分子形成的原子的起源。经常报道有机分子尤其是C ₂二聚体和CN自由基的进化形成途径。但是，对于激光烧蚀等离子体中金属自由基和异二聚体的形成途径了解甚少。这项研究的重点是从¹⁸ O标记的Al ₂ O ₃阐明飞秒激光烧蚀血浆中AlO自由基的形成途径颗粒。在飞秒激光产生的弱电离通道的作用下，产生了在垂直于样品表面的方向上以强正向偏压扩展的等离子体。通过单色快速门控成像，时空分辨光发射光谱和LAMIS等多种等离子体诊断方法研究了AlO的形成机理和空气的影响。使用先进的LAMIS拟合程序来推导Al ¹⁸ O和Al ¹⁶ O数密度的时空分布及其比率。我们发现Al ¹⁶ O / Al ¹⁸靠近样品表面的血浆部分的O数密度比较高，这表明血浆羽流与周围空气之间的化学反应在血浆尾部更为强烈。结果还表明，游离Al和O原子的直接缔合是等离子体早期形成AlO的主要机理。相比之下，等离子体材料与周围氧分子之间的化学反应和同位素交换效应是在等离子体后期形成AlO和演变Al ¹⁶ O / Al ¹⁸ O数密度比的主要机制。

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Laser Ablation Molecular Isotopic Spectrometry for Molecules Formation Chemistry in Femtosecond-Laser Ablated Plasmas

Recently, laser ablated molecular isotopic spectrometry (LAMIS) has expanded its capability to explore molecules formation mechanism in laser-induced plasma in addition to isotope analysis. LAMIS is a powerful tool for tracking the origination of atoms that is involved in formation of investigated molecules by labeling atoms with their isotopic substitution. The evolutionary formation pathways of organic molecules, especially of C₂ dimers and CN radicals, were frequently reported. However, very little is known about the formation pathways for metallic radicals and heterodimers in laser ablated plasma. This research focuses on elucidating the formation pathways of AlO radicals in femtosecond laser ablated plasma from ¹⁸O-labeled Al₂O₃ pellet. Plasmas expanding with strong forward bias in the direction normal to the sample surface were generated in the wake of a weakly ionized channel created by a femtosecond laser. The formation mechanism of AlO and influence of air were investigated with multiple plasma diagnostic methods such as monochromatic fast gating imaging, spatiotemporal resolved optical emission spectroscopy, and LAMIS. An advanced LAMIS fitting procedure was used to deduce the spatiotemporal distributions of Al¹⁸O and Al¹⁶O number densities and also their ratios. We found that the Al¹⁶O/Al¹⁸O number density ratio is higher for plasma portion closer to the sample surface, which suggests that chemical reactions between the plasma plume and ambient air are more intense at the tail of the plasma. The results also reveals that direct association of free Al and O atoms is the main mechanism for the formation of AlO at the early stage of the plasma. To the contrast, chemical reactions between plasma materials and ambient oxygen molecules and the isotope exchange effect are the dominant mechanisms of the formation of AlO and evolution of Al¹⁶O/Al¹⁸O number density ratio at the late stage of the plasma.

更新日期：2017-07-08

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