Emission following laser-induced breakdown spectroscopy of organic compounds in ambient air

Laser-induced breakdown spectroscopy (LIBS) was applied to nitroaromatic (NC) and polycyclic aromatic hydrocarbon (PAH) samples in ambient air to characterize their resultant emission. Compounds covering various surface, were ablated by use of the second (532-nm) or the fourth (266-nm) harmonic of a nanosecond pulsed Nd:YAG laser. The emission consisted of spectral features related mostly to CNand C2 molecular fragments and to C, H, N, and O atomic fragments. The transitions of the molecular fragments correspond to the CN (B 2sigma+ - X 2sigma+) violet system and the C2 (d 3IIg - a 3IIu) Swan system; the intensity of the former is higher in NCs than in PAHs. The intensity ratios between C2 and CN and between O and N correlate to the molecular structure, suggesting the possibility of distinguishing one chemical class from another and in optimum cases even identifing specific compounds by use of LIBS.