Vibrational emission analysis of the CN molecules in laser-induced breakdown spectroscopy of organic compounds
A. Fernandez-Bravo, T. Delgado, P. Lucena, J.J. Laserna, Spectrochimica Acta, Part B, 2013, 89, 77 – 83
Laser-induced breakdown spectroscopy (LIBS) of organic materials is based on the analysis of atomic and ionic emission lines and on a few molecular bands, the most important being the CN violet system and the C2 Swan system. This paper is focused in molecular emission of LIBS plasmas based on the CN (B2Σ–X2Σ) band, one of the strongest emissions appearing in all carbon materials when analyzed in air atmosphere. An analysis of this bandwith sufficient spectral resolution provides a great deal of information on themolecule, which has revealed that valuable information can be obtained from the plume chemistry and dynamics affecting the excitation mechanisms of themolecules. The vibrational emission of thismolecular band has been investigated to establish the dependence of this emission on the molecular structure of the materials. The paper shows that excitation/emission phenomena of molecular species observed in the plume depend strongly on the time interval selected and on the irradiance deposited on the sample surface. Precise time resolved LIBS measurements are needed for the observation of distinctive CN emission. For the organic compounds studied, larger differences in the behavior of the vibrational emission occur at early stages after plasma ignition. Sincemolecular emission is generallymore complex than that involving atomic emission, local plasma conditions as well as plume chemistry may induce changes in vibrational emission of molecules. As a consequence, alterations in the distribution of the emissions occur in terms of relative intensities, being sensitive to the molecular structure of every single material.