Identification of atomic lines and molecular bands of benzene and carbon disulfide liquids by using LIBS

Abstract

Plasma emission of liquid benzene (C 6 H 6 ) and carbon disulfide (CS 2 ) have been studied by using the laser-induced breakdown spectroscopy (LIBS) technique in air. Atomic lines of carbon, hydrogen, sulfur, nitrogen, and oxygen and molecular emissions of CN and C 2 have been identified. The formation mechanism of C 2 and CN molecules has been discussed. The combustion process and high mole fraction of hydrogen in benzene caused a decreasing atomic line intensity of oxygen and an increasing atomic line intensity of hydrogen with respect to the CS 2 and air. Additionally, more intense CN molecular bands and weak nitrogen atomic lines in the C 6 H 6 spectrum compared to CS 2 have been observed. Furthermore, molecular emissions of C 2 have not been observed in the CS 2 spectrum. The electron temperature and vibrational temperature have been calculated from the atomic lines and molecular band intensity, respectively. Finally, the validity of the local thermodynamic equilibrium (LTE) assumption in this experiment has been shown.

CN and C2 vibrational spectra analysis in molecular LIBS of organic materials

“…3a, b indicate that C 2 emission intensities can be related to the number of aromatic ring present in samples structure. Moreover, this observation is consistent with previous studies [20][21][22][23].…”

“…We observed that the C 2 intensity increases as the sum of (C-C) and (C=C) bonds percentage increases. This result is consistent with the hypothesis of an influence of native CC bonds on the C 2 intensity [20][21][22][23].…”

“…In our previous study [22] on LIBS spectrum of carbon disulfide (CS 2 ) in air, we concluded that the absence of C 2 emission can be related to lack of carbon-carbon bond in this molecule structure. Moreover, in several other works, the absence of C 2 emission in samples LIB spectra is attributed to the lack of native carbon-carbon bond [21,25].…”

“…An efficient strategy for discrimination and identification of organic materials is based on the determination of emission intensity ratios between spectral lines from organic elements [19]. In addition, in the last two decades, it has been shown that a certain number of diatomic molecular fragments such as C 2 and CN also provide useful indications for identification of organic materials [7,8,[20][21][22][23]. Plasma chemistry, which is a complex phenomenon, involves atomic and ionic species and the formation of molecular fragments.…”

“…However, three main routes can be cited: (1) fragmentation of the original compound to directly release carbon dimers and CN molecules, (2) reaction in the plume of atomic and ionic constituents of the original compound with the air surrounding the plasma leading to production of CN and (3) recombination of C and N atoms from the compound in the plasma to produce both C 2 and CN [23]. Many works have investigated the correlation between the molecular structure of an organic compound and the molecular emissions from the laser-induced plasma [7,[20][21][22][23]. StOnge et al [20] studied the plasma emission of graphite and organic samples in ambient air by using LIBS.…”