Identifying C2H4N4 structural isomers using fs-laser induced breakdown spectroscopy

Abstract

Four C₂H₄N₄ structural isomers are investigated with fs laser-induced breakdown spectroscopy. Plasma emissions, C I, H_α, the CN violet system (B²Σ⁺–X²Σ⁺, Δν = 0 sequence) and C₂ swan system (d³Π_g–a³Π_u, Δν = 0 sequence) are measured. The temporal evolution of the characteristic emission intensity is obtained for each emission and their lifetimes are calculated. The lifetimes of the molecular emissions are much longer than those of the atomic emissions. Characteristic emission intensities and lifetime are correlated with the molecular structures of the four isomers to a certain extent. Plasma temperature is extracted by fitting the spectrum of the CN violet system, B²Σ⁺–X²Σ⁺; Δν = 0 sequence, and is weakly correlated with the molecular structures of the four isomers. Using the characteristic emission intensities as input, principal component analysis (PCA) and artificial neural network (ANN) analysis are performed and the individual isomers can be well identified with PCA or ANN.