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

Abstract

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 C ₂ 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 Al ₂O ₃ 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 Al ¹⁸O and Al ¹⁶O number densities and also their ratios. We found that the Al ¹⁶O/Al ¹⁸O number density ratiomore » 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. Finally, 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 Al ¹⁶O/Al ¹⁸O number density ratio at the late stage of the plasma.« less

Authors:

Hou, Huaming  ^[1];

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Mao, Xianglei ^[2]; Zorba, Vassilia ^[2]; Russo, Richard E. ^[3]

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+ Show Author Affiliations

1. Peac Inst. of Multiscale Sciences, Chengdu, Sichuan (China); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Applied Spectra, Inc., Fremont, CA (United States)

Publication Date:

2017-07-03

Research Org.:

Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA), Office of Defense Nuclear Nonproliferation

OSTI Identifier:

1479321

Grant/Contract Number:  

AC02-05CH11231

Resource Type:

Journal Article: Accepted Manuscript

Journal Name:

Analytical Chemistry

Additional Journal Information:

Journal Volume: 89; Journal Issue: 14; Journal ID: ISSN 0003-2700

Publisher:

American Chemical Society (ACS)

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY