RUI: Exploring Differences between Condensed Phase Photolysis and Radiolysis

化学系的化学结构、动力学和机理（CSDM-A）项目将资助韦尔斯利学院的Christopher Arumainayagam教授研究由光和/或电子相互作用驱动的化学反应。Arumainayagam博士设计了探针，用于研究低能电子或光子照射前后超高真空条件下纳米级薄膜的组成。这些探针使他的团队能够观察和表征由辐照引起的细微但重要的化学变化。这一重要的化学反应类别影响低温等离子体在工业上的重要过程，如等离子体蚀刻；使用低能电子代替光子进行高选择性键解离；与复杂有机分子（COM）星际合成特定途径相关的示踪分子鉴定；以及电子和光子在大气过程中的相对作用。计划让女性和少数族裔本科生参与这项研究，以促进STEM劳动力的多样化。这项工作特别寻求评估低能（8ev）电子和光子引发的反应之间的异同。目标系统包括冷凝相氨、水和甲醇，每个系统都使用辐照后程序升温解吸、辐照后红外反射吸收光谱和等温电子/光子刺激解吸进行研究。使用具有亚电离能的电子/光子来避免低能二次电子的产生，从而确保探测到电子和光子辐照之间的根本差异。研究的目的是：(1)测量电子/光子诱导反应和解吸的有效截面，并识别所有的电子/光子诱导反应产物；（ii）研究反应截面和产率与电子/光子通量、入射电子/光子能量和薄膜厚度的关系；（iii）确定辐照后程序升温解吸鉴定的产物是否为新生的辐射分解产物。这些研究旨在确定电子诱导的凝聚相反应是否产生独特的分子种类；以及电子是否比光子更有效地引发特定的凝聚相反应。

With with award, the Chemical Structure, Dynamics, and Mechanisms (CSDM-A) Program of the Division of Chemistry is funding Professor Christopher Arumainayagam at Wellesley College to study chemical reactions that are driven by interactions with light and/or electrons. Dr. Arumainayagam has devised probes to study the composition of nanoscale thin films under ultrahigh vacuum conditions before and after irradiation by low-energy electrons or photons. These probes enable his team to observe and characterize the subtle but important chemical changes induced by irradiation. This important category of chemical reactions impacts low-temperature plasmas used in industrially important processes such as plasma etching; use of low-energy electrons instead of photons for highly selective bond dissociations; identification of tracer molecules associated with specific pathways for interstellar synthesis of complex organic molecules (COM); and the relative roles of electrons and photons in atmospheric processes. Involvement of women and minority undergraduate students in this research is planned to promote diversification of the STEM workforce. The work specifically seeks to assess the differences and similarities between reactions initiated by low-energy ( 8 eV) electrons and photons. Target systems include condensed-phase ammonia, water and methanol, each of which is investigated using post-irradiation temperature programmed desorption, post-irradiation infrared reflection absorption spectroscopy, and isothermal electron/photon-stimulated desorption. Electrons/photons with sub-ionization energies are used to avoid production of low-energy secondary electrons, thereby ensuring that fundamental differences between electron and photon irradiation are probed. Among the objectives of the research are: (i) to measure the effective cross-section for electron/photon-induced reaction and desorption, and to identify all of the electron/photon-induced reaction products; (ii) to study the dependence of the reaction cross-sections and yields on electron/photon fluence, incident electron/photon energy, and film thickness; and (iii) to determine if the products identified by post-irradiation temperature-programmed desorption are nascent radiolysis products. The studies are designed to establish whether electron-induced condensed phase reactions generate unique molecular species; and whether electrons are more effective than photons for initiating specific condensed phase reactions.