1. Many mass spectra are observed in addition to those of nitrogen (28amu) and benzene (78amu) molecules between 1 and 80amu, when the discharge is not generated. The benzene and nitrogen molecules effusing through the orifice are decomposed by the electron beam (acceleration voltage:40V) to ionize the neutral molecules in the mass spectrometer. It is, therefore, obvious that electrons play an important role on benzene decomposition. The emissions of CH reaches its maximum first, then the emissions of H  and CN reach their maxima, and the gas pressure decreases when the decomposition rate increases. Benzene is decomposed into CH and other molecules, and that these fragments of benzene immediately deposit on the electrodes or the wall. Decomposition Of Benzene By A Low Pressure Glow Discharge K.Satoh †, T.Sawada †, T.Naitoh †, H.Itoh †, M.Shimozuma ‡ and H.Tagashira † † Department of Electrical and Electronic Engineering, Muroran Institute of Technology, Muroran 050-8585, Japan ‡ College of Medical Technology, Hokkaido University, Sapporo 060-0812, Japan ksatoh@eee.elec.muroran-it.ac.jp Acknowledgement This work was supported by Grant-in-Aid (No.13750236) of Japan Society for the Promotion of Science. Dept. of Electrical & Electronic Eng. Muroran Institute of Technology Motivation Motivation  BENZENE  BENZENE contained in exhaust fumes of automobiles, coke furnaces, chemical factories, etc. is a toxic substance which causes cancer and other disease, so that it needs to be removed or decomposed before it is released in the air. the destruction of benzene ring is one of the dominant reduction processes of dioxins  Yasui et al. (Proc. of GD2000, vol.2, pp.692-5, 2000) reported that the destruction of benzene ring is one of the dominant reduction processes of dioxins in pulse corona discharge, so that the information about the decomposition characteristics of benzene in glow discharges would contribute to decomposition of dioxins using discharge plasma. Previous work Previous work benzene was decomposed by DC discharges in noble gases(Ne and Ar)  McCorkle et al. (J. Phys. D:Appl. Phys., vol.32, pp.46-54, 1999) reported that benzene was decomposed by DC discharges in noble gases(Ne and Ar). They suggested that the dissociative attachment by slow electrons to the benzene molecules in high Rydberg state could be a dominant process for benzene decomposition. nitrogen ion could contribute to destruction of benzene ring  Morris(Bulletin of The American Physical Society, vol.43, pp.1412-3, 1998) suggested that nitrogen ion could contribute to destruction of benzene ring.  Decomposition characteristics, however, are not investigated in detail in these papers. Objective Objective  Investigating the decomposition process of diluted benzene with nitrogen in a low pressure DC glow discharge. Gas-Confined Experiment Gas-Confined Experiment  C 6 H 6 (10%)-N 2 (90%) mixture  Gas pressure: p=133Pa  Gap length: d=1.0cm  Discharge current: I=5mA  The temporal variations of  emission spectra is measured by Photonic Multi-Channel Analyzer.  benzene concentration is measured by GASTEC.  infrared absorption spectra of the film deposited on a silicon wafer on the lower electrode is measured by FTIR. Emission spectraEmissions-CH, H & CN Gas-Flow Experiment Gas-Flow Experiment ★ C 6 H 6 (8%)-N 2 (92%) mixture ★ Gas pressure: 8.7Pa ★ Gap length: 2.5cm ★ Discharge current: 1mA ★ The temporal variations of  emission spectra is measured by Photonic Multi-Channel Analyzer.  mass spectra is measured by Quadrupole Mass Spectrometer. Mass spectra Voltage & pressure Decomposition rate Introduction Experimental Apparatus & Procedure Results (1) – Gas-Confined Experiment Emission-nitrogen Deposition Decomposition rate of benzene increases almost linearly against time first, and then it tends to be constant around 200s. The profile of the decomposition rate is similar to that of the ratio of 1N00/2P00* from which electron mean energy can be inferred. Electrons collide selectively with benzene molecules first because of its large collision cross section, and that the energy of the electrons is transferred to benzene through inelastic collision. When benzene concentration decreases, the emissions of 1N00 and 2P00 and the ratio 1N00/2P00, namely, electron mean energy increase. Electrons escaping a collision with benzene molecule can increase their energy and have excitation and ionization collisions with nitrogen molecules. It is estimated that the energy to decompose benzene is lower than the threshold energies of nitrogen electronic excitations. The emission peak of H  appears behind that of CH. Destruction of benzene ring is more dominant process than dissociation of hydrogen atom from benzene ring. This is similar to the result obtained by Yasui et al* for decomposition of dioxins The absorption spectrum of CH is observed from 50sec, however, the absorption spectra of CN and NH, which are regarded as by-products by the interaction between benzene or its fragments and excited nitrogen molecules (N 2 * ) and/or nitrogen ions (N 2 + ), are observed from 190sec, namely, the time when most of the benzene is decomposed. Benzene is chiefly decomposed by the collision with electrons. N 2 * and/or N 2 + do not make a large contribution to benzene destruction directly. Results (2) – Gas-flow Experiment Mass spectra of 2, 3, 24, 25 and 26amu vary in the opposite manner to that of benzene against time. Similar tendency is seen in the temporal variations of mass spectra of 12, 13, 16 and 17amu, although the intensities of those spectra are low and fluctuated. H 2, H 3, C, CH, CH 4, NH 3, C 2, C 2 H, C 2 H 2 and CN are produced in the glow discharge. The spectrum of 28amu increases fractionally when the discharge is generated. C 2 H 4 is produced. From the emission spectra, H (1amu) is judged a fragment of benzene Conclusions Decomposition process of benzene in the glow discharge is investigated in this work. In the gas-confined experiment  It is likely that benzene is decomposed into CH and other fragments chiefly by electrons the energy of which is lower than the threshold energies of nitrogen electronic excitations, and then some of CH are deposited on the electrodes or wall.  It is also likely that N 2 * and/ or N 2 + do not make a large contribution to benzene destruction directly. In the gas-flow experiment  It is found that H, H 2, H 3, C, CH, CH 4, NH 3, C 2, C 2 H, CN, C 2 H 2, and C 2 H 4 are produced in the glow discharge in the benzene-nitrogen mixture gas. Mass spectraEmission spectra Voltage & pressure *1N00:First negative(0,0) band (391.44nm) 2P00:Second positive(0,0) band (337.13nm) *Proceedings of the XIII International Conference on Gas Discharges and their Applications, Vol.2, 2000, pp.692-695