fs laser-induced filament study of aliphatic nitroalkanes: correlation between molecular structure and spectroscopic evolution of the filament.

Three aliphatic nitroalkanes, nitromethane, nitroethane, and 1-nitropropane, are investigated with fs laser-induced filament and breakdown spectroscopy (LIFBS). Filament emission spectra, C I, the CN violet system (B 2 Σ + - X 2 Σ + , Δ ν = 0 sequence), and the C 2 swan system (d 3 Π g - a 3 Π u , Δ ν = 0 sequence), are obtained. The time integrated intensities of CN and C 2 can be used for identifying the three nitroalkanes. The filament features (length, diameter, and temperature) of the CN and C 2 emissions are analyzed; C 2 converts to CN through a single-atom substitution reaction between C 2 and N atoms at the early stage, which mainly occurs at the head and tail parts of the filament with a lower temperature rather than at the hotter middle part.