the 23th ANNUAL MEETING - CONFERENCE & EXHIBITION

21-22 JANUARY 2020, THE DAVID INTERCONTINENTAL HOTEL, TEL AVIV, ISRAEL

Molecular Emission in Laser Induced Plasma

Michael Gaft, Department of Physics, Ariel University, Ariel, Israel (michael.gaft@gmail.com)
Lev Nagli, Department Of Physics, Ariel University, Ariel, Israel
Yosef Raichlin, Department Of Physics, Ariel University, Ariel, Israel

Molecular analysis by LIBS refers to the spectra emitted by different molecules and diatomic radicals present in the plasma and resulting from the ablation of the target or from subsequent chemical reactions with the ambient air. Molecular spectroscopy with LIBS could be considered a contradictive term, since the high temperatures provided by the plasma would dissociate completely any molecular species present. Nevertheless, since the plasma evolves in time and cools down, an appropriate selection of the experimental parameters (laser energy, delay time, gate width) allows the observation of molecular emission. The well-known examples are CN, CH, C2 Swan system, CaO, AlO, TiO and OH emission spectra in air. Several new molecular emissions have been recently found which are scienti´Čücally and practically important.

The first grope contains halogens F, Cl, Br, I which are difficult to detect because of their energy level distribution with the strongest emission lines are in the VUV spectral range where the detection capability is limited by atmospheric and materials absorption. It was found that in Laser Induced Plasma (LIP) halogens form molecules with alkaline earth elements whose spectra may be easily identified and their sensitivity for halogens analysis is substantially better than by atomic and ionic emission. The typical examples are Me(Ca, Ba, Mg)X(F, Cl, Br, I) molecules. Molecular emission enables to detect F and Cl during Curiosity mission on Mars.

The second grope contains rare-earth elements (REE) where their detection by LIBS is often difficult due to the significant spectral interferences and low content of REE in the main geochemical materials. Molecular emission of YO, LaO and ScO presents an additional opportunity which in many cases is more sensitive than atomic and ionic lines. In luminescent matrixes Plasma Induced Luminescence (PIL) enables to detect other REE, such as Eu, Nd, Tb, Gd, Sm, Dy, Pr.

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