York Plasma Institute, Department of Physics, University of York, Heslington, York YO10 5DD, UK.
Phys Chem Chem Phys. 2018 Sep 26;20(37):24263-24286. doi: 10.1039/c8cp02473a.
Atmospheric pressure plasmas are sources of biologically active oxygen and nitrogen species, which makes them potentially suitable for the use as biomedical devices. Here, experiments and simulations are combined to investigate the formation of the key reactive oxygen species, atomic oxygen (O) and hydroxyl radicals (OH), in a radio-frequency driven atmospheric pressure plasma jet operated in humidified helium. Vacuum ultra-violet high-resolution Fourier-transform absorption spectroscopy and ultra-violet broad-band absorption spectroscopy are used to measure absolute densities of O and OH. These densities increase with increasing H2O content in the feed gas, and approach saturation values at higher admixtures on the order of 3 × 1014 cm-3 for OH and 3 × 1013 cm-3 for O. Experimental results are used to benchmark densities obtained from zero-dimensional plasma chemical kinetics simulations, which reveal the dominant formation pathways. At low humidity content, O is formed from OH+ by proton transfer to H2O, which also initiates the formation of large cluster ions. At higher humidity content, O is created by reactions between OH radicals, and lost by recombination with OH. OH is produced mainly from H2O+ by proton transfer to H2O and by electron impact dissociation of H2O. It is lost by reactions with other OH molecules to form either H2O + O or H2O2. Formation pathways change as a function of humidity content and position in the plasma channel. The understanding of the chemical kinetics of O and OH gained in this work will help in the development of plasma tailoring strategies to optimise their densities in applications.
大气压等离子体是生物活性氧和氮物种的来源，这使得它们有可能被用作生物医学设备。在这里，实验和模拟相结合，研究了在射频驱动的大气压等离子体射流中形成关键活性氧物种，即原子氧（O）和羟基自由基（OH）的过程，该射流在加湿氦气中运行。真空紫外高分辨率傅里叶变换吸收光谱和紫外宽带吸收光谱用于测量 O 和 OH 的绝对密度。这些密度随着进气中 H2O 含量的增加而增加，并在更高的混合物（约 3×1014 cm-3 的 OH 和 3×1013 cm-3 的 O）下接近饱和值。实验结果用于基准零维等离子体化学动力学模拟获得的密度，该模拟揭示了主要的形成途径。在低湿度含量下，O 通过质子转移到 H2O 从 OH 形成，这也引发了大团簇离子的形成。在较高的湿度含量下，O 通过 OH 自由基之间的反应形成，并通过与 OH 的复合而损失。OH 主要由 H2O+通过质子转移到 H2O 和 H2O 的电子碰撞解离形成。它通过与其他 OH 分子的反应损失，形成 H2O + O 或 H2O2。形成途径随湿度含量和等离子体通道中的位置而变化。本工作中对 O 和 OH 化学动力学的理解将有助于开发等离子体定制策略，以优化其在应用中的密度。
