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

Abstract

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 (B²Σ⁺ − X²Σ⁺, Δν = 0 sequence), and the C₂ swan system (d³Π_g − a³Π_u, Δν = 0 sequence), are obtained. The time integrated intensities of CN and C₂ can be used for identifying the three nitroalkanes. The filament features (length, diameter, and temperature) of the CN and C₂ emissions are analyzed; C₂ converts to CN through a single-atom substitution reaction between C₂ 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.