One of the great difficulties in understanding nitrogen plasma elementary processes is the lack of an available database of the cross-sections of electron-impact excitations and radiations.Ab initio calculations of vibrational excitation cross sections for electron collisions with nitrogen molecules in low-lying states using similarity function approach,such as a-a,a-w,B-B and B-W transition systems,are reported here for the first time. In the meantime,the average excitation energies of neighboring levels of these systems have been calculated. In order to obtain the cross sections,accurate spectroscopic constants and transition dipole moments have been investigated.Potential energy curves and other electronic transition dipole moments for the low-lying states of N2have been re-evaluated using complete active space self-consistent field(CASSCF) approach with aug-cc-pVqZ basis set. The calculated cross-sections could provide a database for studying the elementary processes and the properties in N2plasma.
A highly-sensitive in-situ diagnosis approach for nitrogen dioxide(NO2) has been developed in dielectric barrier discharge(DBD) based on pulsed cavity ring-down spectroscopy(CRDS). Absorption bands of NO2in a spectral region from 508 nm to 509 nm were used,and a detection limit of 17.5 ppb was achieved. At this level of sensitivity,the quantitative and real-time monitoring of the production and removal of NO2are accomplished for the first time in the discharge region. By measuring the removal amount and rate at different NO2initial number densities from 1.54 × 1013cm-3to 2.79 × 1014cm-3,we determined the relationship between them and NO2initial number densities. The removal amount linearly increases with the initial number density,while the removal rate increases logarithmically. At a lower initial number density,the removal rate is limited. By considering the chemical kinetic mechanism in plasma,a qualitative explanation for the above phenomena is proposed:the additional NO2produced by discharge limits the removal rate,since the NO2concentration is dominated by the competition between the forward reactions(production) and the reverse reactions(removal).
Laser-induced breakdown spectroscopy(LIBS) is a powerful analytical tool for realtime diagnostics and detection of multiple elements deposited at the first wall of magnetically confined plasma fusion devices. Recently,we have tested LIBS in our laboratory for application to in situ real-time diagnostics in the fusion device EAST. In this study,we applied polarizationresolved LIBS(PR-LIBS) to reduce the background continuum and enhance the resolution and sensitivity of LIBS. We used aluminium(Al)(as a substitute for Be) and the first wall materials tungsten(W) and molybdenum(Mo) to investigate polarized continuum emission and signal-tobackground ratio(SBR). A Nd:YAG laser with first,second and third harmonics was used to produce plasma. The effects of the laser polarization plane,environmental pressure and polarizer detection angle were investigated. The spectra obtained without using a polarizer(i.e. LIBS)were compared with those obtained with a polarizer(PR-LIBS). Distribution of emission spectral intensity was observed to follow Malus' law with respect to variation in the angle of detection of the polarizer. The spectra obtained by PR-LIBS had a higher SBR and greater stability than those obtained by LIBS,thereby enhancing the reliability of LIBS for quantitative analyses.A comparison of Al,Mo and W showed that W exhibited a higher continuum with stronger polarization than the low-Z elements.
In this paper,a low pressure Ar/N2 shock plasma jet with clearly multicycle alternating zones produced by a DC cascade arc discharge has been investigated by an emission spectral method combined with Abel inversion analysis.Plasma emission intensity,electron,vibrational and rotational temperatures of the shock plasma have been measured in the expansion and compression zones.The results indicate that the ranges of the measured electron temperature,vibrational temperature and rotational temperature are 1.1 eV to 1.6 eV,0.2 eV to 0.7 eV and 0.19 eV to 0.22 eV,respectively,and it is found for the first time that the vibrational and rotational temperatures increase while the electron temperature decreases in the compression zones.The electron temperature departs from the vibrational and the rotational temperatures due to non-equilibrium plasma efects.Electrons and heavy particles could not completely exchange energy via collisions in the shock plasma jet under the low pressure of 620 Pa or so.
<正> Benzene is a major industrial air pollutant and can cause serious human healthdisorders.In this paper an investigation on benzene destruction,in an atmospheric-pressure fast-flow pulsed DC-discharge by means of laser ionization combined with time-of-flight(TOF)massspectrometry,is reported.Most by-products including transient reactive species from the benzenedischarge were characterized by molecular beam sampling combined with TOF mass spectrometry.It is showed that,with a gas mixture of 0.5% C_6H_6 in Ar,benzene can be effectively destroyedby discharge plasma.The intermediate species consisted of small fragments of C_nH_m(n=3~5,m=1~11),cycle-chain species of C_nH_m(n=6~9,m=7~10)and polycyclic species C_nH_m(n≥9,m=8~12).The alternation of mass peaks(intensity)with even/odd electrons was observed in themeasured mass spectra.The results indicated that the alternation is mainly due to the differentionization potentials of the open shell and close shell species.Based on the examination of thefeatures of the species' composition,the primary reaction pathways are proposed and discussed.
<正>The behavior of argon plasma in a low pressure driven by nano-second pulsed plasma reactor is investigated ...
Xueqing Wen,Cnunlei Feng,Yu Xin,Hongbin Ding~ School of Physics and Optical Electronic Technology,Dalian University of Technology,Dalian 116024,PR China
