The crucial role of molecular emissions on LIBS differentiation of organic compounds of interest in astrobiology under a Mars simulated atmosphere

In this work, the influence of Martian atmosphere on the recombination mechanisms in laser-induced plasmas of organic compounds of interest in astrobiology has been closely examined. The proposed LIBS methodology reveals new insights concerning the influence of the surrounding atmosphere on the molecular emission of organics. The presence of nitrogen, even in the short concentration found in the low-pressure Mars environment, influences the plasma chemistry and the formation pathways leading to molecular species. Characteristic atomic and molecular emitters (C, H, C2, CN, NH, OH and CH) were inspected in a set of selected organic compounds considered as meaningful biomarkers. For comparative purposes, LIBS analysis was performed in both low-pressure air and Martian atmospheres. Statistical analysis (linear discriminant analysis; DFA) suggested that satisfactory differentiation among materials was feasible under Martian conditions when molecular emissions are computed in the classification algorithm. Atomic lines (C, H) only contribute a mere ~62% to the discriminating analysis, whereas the percentage of successful discrimination was considerably increased (up to 99%) by the progressive introduction of signals associated to molecular bands into the DFA analysis, thus confirming the major contribution of molecular information to the final sorting performance and the feasibility of discriminating closely related organic compounds by LIBS in the Martian atmosphere.