CaCl and CaF emission in LIBS under simulated martian conditions

Abstract

Chlorine and fluorine play an important role in the geological history of Mars due to their high concentration in Martian magmas and their influence on the generation and evolution of Martian basalts. Chlorine-bearing salts could also facilitate the formation of eutectic brines that could be important for the fluvial history of Mars. The LIBS instruments of ChemCam and SuperCam can detect emission lines of Cl and F, but the intensity of these emission lines is comparatively low, making it difficult to quantify them correctly. A promising alternative is the quantification by molecular emission of diatomic molecules like CaCl and CaF, which can be observed as intense molecular bands in LIBS spectra if Ca is also present. However, the nonlinear dependence of the band intensity on the concentrations of both elements needs to be considered. In this study, we expand upon our previous analysis of molecular bands by investigating samples which produce CaCl bands, CaF bands, or both. We find that the highest CaCl band intensities are found in samples containing more Ca than Cl, while the strongest CaF bands are found in samples with roughly equal concentrations of Ca and F. Both observations can Preprint submitted to IcarusJune 20, 2019be described by the model that we present here. We also find that the CaCl band is significantly stronger for a sample containing CaCl 2 than it is for a sample containing the same concentrations of Ca and Cl in separate bonds.The opposite is true for the CaF band, which is significantly weaker for the sample containing CaF 2 bonds than it is for the sample that does not contain CaF 2 bonds. These matrix effects are partially attributed to fragmentation during the ablation process and differences in the dissociation energies. Furthermore, we observe that CaF formation is not affected by competing CaCl formation, while CaCl is strongly affected by competing CaF formation. All measurements are done in simulated Martian atmospheric conditions in order to assist the analysis of Martian LIBS data.

Toward On-Line Slag Composition Analysis: Optical Emissions from Laboratory Electric Arc

“…As emphasized also by Alvarez-Llamas et at. [18,19] and Vogt et al, [21] CaF bands above 590 nm overlap with CaO bands, and thus the CaF bands at 535 and 585 nm show more promise for reliable quantitative analysis.…”

“…X 2 R þ (bands at 585, 605, and 625 nm). [16][17][18][19]21] Regarding the CaO band in the spectrum of Bol'shakov et al, the spectrum between 377 and 745 nm in Figure 5 shows a similar broad band between 590 and 650 nm. Even though there was CaO in every slag sample, the CaO band was not intensive enough to be detected in all of the spectra in the present study.…”

Detecting sulfur on the Moon: The potential of vacuum ultraviolet laser-induced breakdown spectroscopy

“…In ambient atmospheric conditions, the expanding plasma is confined by the surrounding gas and frequent collisions between the plasma species result in an equilibrium state on short timescales, which can be described by a temperature. Studies have shown that this equilibrium temperature for a certain phase after the plasma initiation changes only slightly upon changes in the laser pulse energy and therefore in the irradiance [114,115]. A common explanation for this counter-intuitive behaviour is that the spatial extent of the plasma increases for higher pulse energies, resulting in unchanged density and pressure conditions [115,116].…”

“…Studies have shown that this equilibrium temperature for a certain phase after the plasma initiation changes only slightly upon changes in the laser pulse energy and therefore in the irradiance [114,115]. A common explanation for this counter-intuitive behaviour is that the spatial extent of the plasma increases for higher pulse energies, resulting in unchanged density and pressure conditions [115,116]. Thus, as long as saturation effects such as self-absorption can be neglected, the emission intensity ratios of the spectral lines remain mostly unchanged while the total intensity of the spectrum increases with pulse energy due to a larger amount of ablated mass [27].…”

Improved plasma stoichiometry recorded by laser ablation ionization mass spectrometry using a double‐pulse femtosecond laser ablation ion source

“…Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), Laser-Induced Breakdown Spectroscopy (LIBS), or Laser Ablation Ionization Mass Spectrometry (LIMS), are applied in various fields in academic and industrial research to quantitatively investigate the chemical composition of solid samples. Applications range from, e.g., chemical imaging of highly heterogeneous geological and/or biological samples, [1][2][3][4][5][6][7][8][9] to the dating of solids and mineralogical analysis, 10,11 and to the chemical analysis of high-performance materials used in industry. [12][13][14][15][16] LA-ICP-MS is among the most widespread laser-based analytical technique due to its accurate quantification, high reproducibility, and low limits of detection.…”