Possibility of controlling the chemical pattern of He and Ar 'guided streamers' by means of N_2 or O_2 additives

摘要

Plasma chemistry at atmospheric pressure and low temperature has met an increased interest due to the effective production of reactive species (mainly reactive nitrogen species and reactive oxygen species) which are demanded in many applications like in biomedicine. The generation of such emissive reactive species is herein studied. A single parameter, i.e., the gas composition, is tuned and abundant chemical species are obtained in a quite controllable manner. The system refers to a small dielectric barrier discharge based reactor fed with He-N_2/O_2 or Ar-N_2/O_2 gases, which provides plasma in the form of "guided streamers." The plasma is sustained by positive high voltage pulses, and the emissive transitions versus the gas composition is determined by UV-VIS optical emission spectroscopy. The relative intensities of emissive species are recorded in the ambient air where the streamers propagate. The evolution of dominant species as a function of the gas composition is mapped, and optimal conditions in terms of species production are clearly revealed. The results show that additives do not necessarily enhance the density of all species, implying the need for plasma chemistry optimization in respect to every application. The study is extended inside the reactor, supporting the above statements. Finally, the rotational and vibrational distributions of critical probe molecules are recorded, testing the dependence of the gas temperature and energy transfer, respectively, on the gas composition.