Correlation of molecular, atomic emissions with detonation parameters in femtosecond and nanosecond LIBS plasma of high energy materials

Abstract

In the present work, six novel high energy materials (HEMs) were investigated by femtosecond and nanosecond LIBS techniques with an intention to comprehend the influence of different functional groups as well as their positions on the LIBS emission. The examined HEMS are functional and structural isomers of triazole-substituted nitroarene derivatives and have methyl (CH₃), methoxy (OCH₃), and amino (NH₂) groups in ortho and para positions. CN and C₂ molecular bands along with atomic lines of C, H, N and O were identified in the ns and fs LIBS spectra. As expected, the molecular signatures in the earlier times of plasma expansion were observed to be prominent in femtosecond LIBS spectra. The various formation pathways for CN and C₂ as well as the correlation of emission intensities with C–C, CC, C–N, and CN bonds and % O are investigated using the fs and ns LIBS data recorded in air and argon atmospheres. The influence of functional groups and their position on CN and C₂ emissions is elucidated through the CN/C₂ ratio. Furthermore, the detonation parameters of these materials namely oxygen balance, velocity of detonation, detonation pressure and chemical energy of detonation were found to correlate well with the (CN + C₂)/(C + H + N + O) ratio. Such correlation studies are expected to support the understanding and improve the discrimination procedures for such hazardous materials.