Considerations on formation mechanisms of emitting species of organic and C-containing inorganic compounds in CO2 atmosphere using LIBS as a strategy for detection of molecular solid

Abstract

Detection of organic matter in CO2 atmosphere at low pressure using laser-induced breakdown spectroscopy is an arduous and complex task due to different carbon-related sources that may participate in the emission signals. This research focuses on assessing the effect of a CO2 surrounding atmosphere at 7 mbar on the formation of emitting species in laser-induced plasmas of C-containing compounds and on identifying three possible sources of carbon species: the organic compound, the inorganic matrix, and the atmosphere. Four organic compounds (adenine, glycine, pyrene and urea) were chosen due to their different molecular structures and chemical composition for the study. The influence of their molecular structure on the intensity of molecular (C2 and CN) and atomic (C, H, N and O) emissions were explored. They were used as dopants at different concentrations in inorganic matrices such as CaCO3 and CaSO4.2H2O. In order to understand the breakage pattern of the organic molecules, the study was also carried out in air (7 mbar). Differences in relative intensities of emitting species as a function of both the chemical structure and the tested surrounding atmosphere were observed. Larger intensities were observed in CO2 atmosphere compared to air. This finding confirms the contribution of the CO2 on formation routes of atomic C (I) and diatomic carbon C2, even in non‑carbon compounds such as CaSO4.2H2O. The plasma emission threshold fluence of organic molecules in the inorganic matrices was also established. Lower threshold values for C-emitting species, in the case of carbonate matrix, were measured in presence of CO2 ambient gas.