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Review on recent advances in analytical applications of molecular emission and modelling
Spectrochimica Acta Part B: Atomic Spectroscopy ( IF 3.3 ) Pub Date : 2020-11-01 , DOI: 10.1016/j.sab.2020.105989
Michael Gaft , Lev Nagli , Igor Gornushkin , Yosef Raichlin

Abstract The review mainly deals with two topics that became important in applications of laser-induced breakdown spectroscopy (LIBS) in recent years: the emission of halogen- and rare-earth-containing molecules and selective excitation of molecules by molecular laser-induced fluorescence (MLIF). The first topic is related to the emission of alkaline-earth diatomic halides MX, M = Ca, Mg, Ba, Sr and X = F, Cl, Br, and I and rare-earth element (REE) oxides LaO, YO, and ScO. These molecules form in laser-induced plasma (LIP) soon after its ignition and persist for a long time, emitting broad bands in a visible part of the spectrum. They are best detected after relatively long delay times when emission from interfering plasma species (atoms and ions) has already been quenched. Such behavior of molecular spectra allows of using, for their detection, inexpensive CCD detectors equipped with simple electronic or mechanical shutters and low-resolution spectrometers. A main target for analysis by molecular spectroscopy is halogens; these elements are difficult to detect by atomic spectroscopy because their most intense atomic lines lie in the vacuum UV. Therefore, in many situations, emission from CaF and CaCl may provide a substantially more sensitive detection of F and Cl than emission from elemental F and Cl and their ions. This proved to be important in mining and concrete industries and even Mars exploration. A similar situation is observed for REEs; their detection by atomic spectroscopy sometimes fails even despite the abundance of atomic and ionic REEs' lines in the UV-VIS. For example, in minerals and rocks with low concentrations of REEs, emission from major and minor mineral elements hinders the weak emission from REEs. Many REEs do not form molecules that show strong emission bands in LIP but can still be detected with the aid of LIP. All REEs except La, Y, and Sc exhibit long-lived luminescence in solid matrices that is easily excited by LIP. The luminescence can be detected simultaneously with molecular emission of species in LIP within the same time and spectral window. The second topic is related to the combination of MLIF and LIBS, which is a technique that was proved to be efficient for analysis of isotopic molecules in LIP. For example, the characteristic spectral signals from isotopic molecules containing 10B and 11B are easier to detect with MLIF-LIBS than with laser ablation molecular isotopic spectrometry (LAMIS) because MLIF provides strong resonance excitation of only targeted isotopes. The technique is also very efficient in detection of halogen molecules although it requires an additional tunable laser that makes the experimental setup bulky and more expensive.

中文翻译:

分子发射和建模分析应用的最新进展综述

摘要 该综述主要涉及近年来在激光诱导击穿光谱 (LIBS) 应用中变得重要的两个主题:含卤素和稀土分子的发射和分子激光诱导荧光对分子的选择性激发。 MLIF)。第一个主题与碱土双原子卤化物 MX、M = Ca、Mg、Ba、Sr 和 X = F、Cl、Br 和 I 以及稀土元素 (REE) 氧化物 LaO、YO 和斯科。这些分子在点燃后不久在激光诱导等离子体 (LIP) 中形成并持续很长时间,在光谱的可见部分发出宽频带。当干扰等离子体物质(原子和离子)的发射已经被淬灭时,它们最好在相对较长的延迟时间后检测到。分子光谱的这种行为允许使用,用于它们的检测,配备简单电子或机械快门和低分辨率光谱仪的廉价 CCD 探测器。分子光谱分析的主要目标是卤素;这些元素很难被原子光谱检测到,因为它们最强烈的原子线位于真空紫外线中。因此,在许多情况下,与元素 F 和 Cl 及其离子的发射相比,CaF 和 CaCl 的发射可以提供明显更灵敏的 F 和 Cl 检测。事实证明,这在采矿和混凝土行业甚至火星探索中都很重要。对 REE 观察到类似情况;尽管在 UV-VIS 中有大量的原子和离子 REE 谱线,但它们的原子光谱检测有时也会失败。例如,在稀土元素浓度较低的矿物和岩石中,主要和次要矿物元素的发射阻碍了稀土元素的弱发射。许多 REE 不会形成在 LIP 中显示出强发射带的分子,但仍然可以借助 LIP 进行检测。除 La、Y 和 Sc 外,所有 REE 在固体基质中都表现出长寿命发光,很容易被 LIP 激发。在相同的时间和光谱窗口内,可以同时检测到发光与 LIP 中物种的分子发射。第二个主题与 MLIF 和 LIBS 的组合有关,该技术已被证明可有效分析 LIP 中的同位素分子。例如,MLIF-LIBS 比激光烧蚀分子同位素光谱法 (LAMIS) 更容易检测来自含有 10B 和 11B 的同位素分子的特征光谱信号,因为 MLIF 仅提供目标同位素的强共振激发。该技术在检测卤素分子方面也非常有效,尽管它需要额外的可调谐激光器,这使得实验装置体积庞大且成本更高。
更新日期:2020-11-01
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