Excited States in Surface Photochemistry

9417866本研究的目的是探索吸附质和底物激发态的能量和寿命，并了解激发态弛豫过程与所观察到的光化学产物之间的联系。利用可调激光泵浦-探针结构中的双光子光发射来测量激发态的能量和寿命。质谱仪和高分辨率电子能量损失光谱仪提供光化学产品的化学信息。六硼化镧（100）独特的低功函数可作为模型金属底物，在其上吸附具有不同电子亲和度的分子。带隙对弛豫过程的影响将在清洁和预吸附k的氮化镓薄膜上进行研究。研究了氧与一氧化碳在铂上共吸附的光化学反应以及一氧化碳在硅上的光解吸。%%%%表面光化学与表面激发态的松弛密切相关。关于表面激发态的信息非常少，尽管它们在表面光化学中很重要。光子吸收之后的微观步骤在很大程度上是未知的，最多只能从最终产物的分布中推测出来。表面光化学的两个最重要和最广泛的机制是：1。2.吸附分子的直接电子激发；底物激发之后是光生热载流子与被吸附分子的相互作用。本研究的目的是探索吸附质和底物激发态的能量和寿命，并了解激发态弛豫过程与所观察到的光化学产物之间的联系。

9417866 The objectives of the proposed research are to probe the energies and lifetimes of the adsorbate and substrate excited states and to understand the connection between the excited state relaxation processes and the observed photochemical products. Two-photon photoemission in the pump-probe configuration with a tunable laser will be used to measure the energies and lifetimes of the excited states. A mass spectrometer and a high-resolution electron energy loss spectrometer provide chemical information on the photochemical products. The uniquely low work function of Lanthanum hexaboride(100) serves as a model metal substrate on which molecules with different electron affinities are adsorbed. The effects of a band gap on the relaxation processes will be investigated on clean and K-preadsorbed gallium nitride thin films. Studies on the photochemistry of oxygen coadsorbed with carbon monoxide on platinum and the photodesorption of carbon monoxide from silicon will be pursued. %%%% Surface photochemistry is intimately connected to the relaxation of excited states at the surface. Information on the excited states at surfaces is very scarce, despite their importance in surface photochemistry. The subsequent microscopic steps following absorption of photons are largely unknown and at best conjectured from the distribution of end products. It has been firmly established that the two most important and widespread mechanisms of surface photochemistry are: 1. direct electronic excitation of the adsorbed molecules, and 2. substrate excitation followed by interactions of photogenerated hot carriers with the adsorbed molecules. The objectives of the proposed research are to probe the energies and lifetimes of the adsorbate and substrate excited states and to understand the connection between the excited state relaxation processes and the observed photochemical products.