Due to the operation at background pressures between 10-40 mbar and high reduced electric field strengths of up to 120 Td, the ion-molecule reactions in High Kinetic Energy Ion Mobility Spectrometers (HiKE-IMS) differ from those in classical ambient pressure IMS. In the positive ion polarity mode, the reactant ions H+(H2O)n, O2+(H2O)n, and NO+(H2O)n are observed in the HiKE-IMS. The relative abundances of these reactant ion species significantly depend on the reduced electric field strength in the reaction region, the operating pressure, and the water concentration in the reaction region. In this work, the formation of negative reactant ions in HiKE-IMS is investigated in detail. On the basis of kinetic and thermodynamic data from the literature, the processes resulting in the formation of negative reactant ions are kinetically modeled. To verify the model, we present measurements of the negative reactant ion population in the HiKE-IMS and its dependence on the reduced electric field strength as well as the water and carbon dioxide concentrations in the reaction region. The ion species underlying individual peaks in the ion mobility spectrum are identified by coupling the HiKE-IMS to a time-of-flight mass spectrometer (TOF-MS) using a simple gated interface that enables the transfer of selected peaks of the ion mobility spectrum into the TOF-MS. Both the theoretical model as well as the experimental data suggest the predominant generation of the oxygen-based ions O-, OH-, O2-, and O3- in purified air containing 70 ppmv of water and 30 ppmv of carbon dioxide. Additionally, small amounts of NO2- and CO3- are observed. Their relative abundances highly depend on the reduced electric field strength as well as the water and carbon dioxide concentration. An increase of the water concentration in the reaction region results in the generation of OH- ions, whereas increasing the carbon dioxide concentration favors the generation of CO3- ions, as expected.

中文翻译：

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高动能离子迁移谱（HiKE-IMS）中的负反应离子形成。

由于在10-40 mbar的背景压力和高达120 Td的高降低电场强度下运行，因此高动能离子迁移谱仪（HiKE-IMS）中的离子分子反应与经典环境压力IMS中的离子反应不同。在正离子极性模式下，在HiKE-IMS中观察到反应物离子H +（H2O）n，O2 +（H2O）n和NO +（H2O）n。这些反应物离子种类的相对丰度在很大程度上取决于反应区域中电场强度的降低，操作压力和反应区域中水的浓度。在这项工作中，详细研究了HiKE-IMS中负反应离子的形成。根据来自文献的动力学和热力学数据，对形成负反应离子的过程进行了动力学建模。为了验证该模型，我们介绍了HiKE-IMS中负反应离子的数量及其对降低的电场强度以及反应区域中水和二氧化碳浓度的依赖性。通过使用简单的门控界面将HiKE-IMS与飞行时间质谱仪（TOF-MS）耦合，可以识别离子迁移谱中各个峰以下的离子种类，从而实现离子迁移谱的选定峰的转移进入TOF-MS。理论模型和实验数据均表明，在含70 ppmv水和30 ppmv二氧化碳的纯净空气中，主要生成基于氧的离子O-，OH-，O2-和O3-。此外，观察到少量的NO2-和CO3-。它们的相对丰度高度取决于降低的电场强度以及水和二氧化碳的浓度。如所期望的，反应区域中水浓度的增加导致OH-离子的产生，而二氧化碳浓度的增加有利于CO3-离子的产生。