1. Decomposition rate of benzene increases almost linearly against time, and it tends to be constant around 200s. While the decomposition rate increases, gas pressure decreases. The fragments of benzene immediately deposit on the electrodes or the wall of the discharge chamber. The temporal variation of the ratio of 1N/2P from which electron mean energy can be inferred is similar to that of decomposition rate. Energy of electrons is transferred to benzene through inelastic collision, and benzene is decomposed by the energy. Emission of CH reach its maxcimam first, then the emission of H  and CN reach their maxcima. The absorbance of CH bond is observed from 50s, and the increase of the absorbance almost ceases after 190s, while the absorbance of CN bond is observed at 190s for the first time. CH molecules are generated by destruction of benzene first, and some of CH molecules are deposited on the wafer. CN, H and NH are formed by the interaction between CH and electrons, N 2 * or N 2 +. If CH and H are generated simultaneously at the destruction of benzene, the emission of H  should be observed at the beginning of the discharge. However, the result shows very low emission intensity of H  at the beginning. 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. (Namely, destruction of benzene ring is more dominant than dissociation of chlorine atom from benzene rings of dioxins.) Dept. of Electrical & Electronic Eng. Muroran Institute of Technology ● Motivation  BENZENE contained in exhaust fumes of coke furnace, chemical factories, automobiles, etc. is a source of air pollution and benzene is a toxic substance which has carcinogenesis. Therefore, it is needed to develop the technique for removing or decomposing benzene in the exhaust fumes. Previous work  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.  Morris(Bulletin of The American Physical Society, vol.43, pp.1412-3, 1998) suggested that nitrogen ion could contribute to destruction of benzene ring.  However, decomposition characteristics are not investigated in detail in these papers. ● Objective  Investigating the decomposition characteristics of benzene in a low pressure DC glow discharge in pure benzene and benzene-nitrogen mixture.  Yasui et al(Proceedings of the XIII International Conference on Gas Discharge and their Applications, vol.2, pp.692-5, 2000) reported that DIOXINs are decomposed by dissociation of C-O bond and destruction of benzene ring. Therefore, data obtained here can make contribution to decomposition of DIOXINs. 1. Introduction 2. Experimental Apparatus & Procedure Electrode : Parallel plate, φ60mm Discharge Chamber : φ155mm×300mm height Purity : Benzene 99%, Nitrogen 99.999%  Negative DC voltage is applied to the upper electrode to generate discharge in pure benzene and in benzene-nitrogen mixture.  The temporal variations of  emission from the discharge is measured by Photonic Multi-channel Analyzer (Hamamatsu PMA -11).  benzene concentration is measured by gas detection tube (GASTEC No.121), and decomposition rate of benzene is calculated.  infrared absorption spectra of the film deposited on a silicon wafer set on the lower electrode is measured by FT-IR (Perkin Elmer Spectrum 2000). P=0.5Torr d=1.0cm I=5mA  At the beginning, emission spectra of benzene (260 ～ 280nm) are observed, and they tend to decrease.  At 360 sec, emission of the fragments of benzene [CH(A 2  →  X 2  :431.42nm), C 2 (468.02 & 516.52nm), H  (656.28nm) and H  (486.02nm)] are observed. Therefore, it is judged that benzene is decomposed by electron collision in the DC glow discharge. 3. Result (1) – In Pure Benzene 5. Effect of Benzene Concentration & Gas Pressure In pure benzene discharge  Benzene is decomposed by electron collision, and the fragments of benzene immediately deposite on electrodes or wall. In benzene-nitrogen discharge  Benzene is decomposed into CH and others by electron collision first, and CH interacts with electrons, excited nitrogen molecules or nitrogen ions, then H, CN etc. are generated.  Correlation between temporal profile of decomposition rate of benzene and that of electron mean energy is found.  Destruction of benzene ring is more dominant process than dissociation of hydrogen atoms from benzene ring.  Benzene is not reproduced from by-products in the discharge. Acknowledgement This research was performed by the support of Grant-in-Aid for Encouragement of Young Scientist of Japan Society for the Promotion of Science. Decomposition Characteristics of Benzene in DC Glow Discharge K. Satoh †, S. Hayashi †, N. Kudoh †, 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@elec.muroran-it.ac.jp 4. Results (2) – In Benzene(10%)-Nitrogen(90%) Mixture P=1.0Torr d=1.0cm I=5.0mA Emission spectra Temporal variation of gas pressure, emission intensity and decomposition rate of benzene Infrared absorption spectra of thin film on a silicon wafer set on the lower electrode  Since the value of the electron total cross section in benzene is much larger than that in nitrogen, electrons are expected to collide with benzene molecules, and CH molecules and etc. are generated.  The mean energy of the electrons is expected to be retained at low value due to the large cross sections of benzene, and the electrons can not generate enough number of N 2 * and/or N 2 + to interact with CH.  Also, the contribution of N 2 * and/or N 2 + to the decomposition of benzene is not large, since the emission of CN and the infrared absorption of CN and NH are not seen at this region. Electron collision cross sections in N 2 and C 6 H 6 600 ～ 950nm 250 ～ 600nm  Benzene is decomposed into CH and others. Nitrogen Q m :momentum transfer,  q v :vibrational excitation,  q ex :electronic excitations, q i :ionization,  q diss :dissociation (Y. Ohmori et al., J. Phys. D:Appl. Phys., Vol.21, 1988, pp.724-9) Benzene (total collision cross section) △ :Gully et al., J.Phys. B: At. Opt. Phys., Vol.31, 1998, pp.2735-51 ＋, ○ :Mozejko et al., Chemical Physics Letters, Vol.257, 1996, pp.309-13 2,3,7,8-TCDD Cl O O H H HH C C C C C C C C C C C C  CN and NH deposit on the electrodes or wall.  Deposition of CH almost ceases. 6. Conclusions  Remaining benzene is decomposed into CH and others.  H, CN, etc. are generated by the interaction between CH and electrons, N 2 * or N 2 +.  Electron energy increases enough to generate N 2 * and N 2 +, and these species and electrons interact with CH. Dissipated energy for decomposing benzene is almost proportional to the partial pressure of benzene, namely, benzene concentration. There is no optimum condition for benzene decomposition for benzene concentration and gas pressure. At 90s, emission of H  and C 2 (809.51nm) regarded as fragments of benzene and a by-product CN (918.95, 787.27nm) are observed