Absolute OH and O radical densities in effluent of a He/H2O micro-scaled atmospheric pressure plasma jet
Absolute OH and O radical densities in effluent of a He/H2O micro-scaled atmospheric pressure plasma jet
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DOI：
10.1088/0963-0252/25/4/045013
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发表时间：
2016-08-01
影响因子：
3.8
通讯作者：
Schulz-von der Gathen, V.
中科院分区：
文献类型：
--
作者：
Benedikt, J.;Schroeder, D.;Schulz-von der Gathen, V.
用腔衰荡激光吸收光谱和分子束质谱测量羟基(OH)自由基密度，用双光子吸收激光诱导荧光光谱测量原子氧(O)密度，分析了微尺度大气压等离子体射流(MU-APPJ)在含有水蒸气(小于或类似于10(4)ppm)的氦气中运行的流出物。此外，还对鼓泡器作为氦原料气中水蒸气来源的性能进行了仔细的表征和校准。在2×10(14)cm(-3)和3.2×10(13)cm(-3)的流出物中测得的最大OH和O浓度分别在6000ppm左右。最高的选择性在1500ppm左右，其中OH浓度接近其最大值的63%，是O浓度的14倍。测量的密度分布和距离变化与二维轴对称流体模型的结果进行了比较，该模型描述了等离子体流出物的输运和反应动力学。结果表明，出水中OH自由基的损失主要是它们之间的相互作用。在O的情况下，还必须考虑与OH以外的其他物种的反应，以解释流出物中的密度衰减。本文的结果为理解非平衡大气压等离子体中的等离子体化学过程提供了补充信息。它们还开辟了将He/H2O作为OH自由基的选择性来源应用于MU-APPJ的途径。
The effluent of a micro-scaled atmospheric pressure plasma jet (mu-APPJ) operated in helium with admixtures of water vapor (less than or similar to 10(4) ppm) has been analyzed by means of cavity ring-down laser absorption spectroscopy and molecular beam mass spectrometry to measure hydroxyl (OH) radical densities, and by two-photon absorption laser-induced fluorescence spectroscopy to measure atomic oxygen (O) densities. Additionally, the performance of the bubbler as a source of water vapor in the helium feed gas has been carefully characterized and calibrated. The largest OH and O densities in the effluent of 2 x 10(14) cm(-3) and 3.2 x 10(13) cm(-3), respectively, have been measured at around 6000 ppm. The highest selectivity is reached around 1500 ppm, where the OH density is at similar to 63% of its maximum value and is 14 times larger than the O density. The measured density profiles and distance variations are compared to the results of a 2D axially symmetric fluid model of species transport and reaction kinetics in the plasma effluent. It is shown that the main loss of OH radicals in the effluent is their mutual reaction. In the case of O, reactions with other species than OH also have to be considered to explain the density decay in the effluent. The results presented here provide additional information for understanding the plasma-chemical processes in non-equilibrium atmospheric pressure plasmas. They also open the way to applying mu-APPJ with He/H2O as a selective source of OH radicals.