Study of the dynamical process for the surface-molecule interaction using laser-induced desorption

用纳秒脉冲紫外激光研究了NO和CO在过渡金属上的电子激发诱导脱附。结果表明，NO和CO从Pt上脱附，而这些分子不从Ni和Pd上脱附。我们试图阐明这种显著选择性的起源。因此，研究脱附过程中中间激发态的性质是十分必要的。观察到NO从Pt（111）上脱附的角分布与速度的关系。角分布的宽度随着速度的增加而变窄，并且与转动能无关。实验结果表明，该模型具有明显的速度依赖性，且速度依赖性太大，不能用简单的模型来解释实验结果。定性结果表明，NO分子在激发态下的受抑平移过程中发生了刚性化，而在受抑转动过程中发生了软化.激光诱导NO从Pt（111）-Ge表面合金表面脱附，而CO不脱附。用光电子能谱观察了合金的电子结构和吸附在该表面上的CO的电子态。合金的带宽度比Pt的带宽度窄。这个结果是合理的。CO 5 σ态在合金上的结合能与在Pt（111）上的结合能几乎相等，而脱附能相差很大。这种矛盾的结果可以用微扰模型来解释.在Pt（111）-Ge表面合金化的1单层Ge表面。用反射吸收红外光谱观察到Ge覆盖层上的绝缘体-金属转变，CO吸附的C-O伸缩振动吸收谱的带宽比Pt（111）、Pt（111）-Ge和多层Ge上的宽得多。

Desorption induced by electronic excitation of NO and CO from transition metals has been studied with a nanosecond-pulsed ultraviolet laser. It was observed that NO and CO are desorbed from Pt while these molecules are not desorbed from Ni and Pd. We have tried to elucidate the origin of this remarkable selectivity.1. It is essential to study thenature of the intermediate excited state in the desorption process. The velocity dependence of the angular distribution for desorbe NO from Pt (111) is observed. The width of the angular distribution becomes sharper with increasing velocity and is independent of therotational energy. A remarkable velocity dependence was observed and is too large to interprete the experimental result by a simple model. Qualitative result shows that stiffening occurs in the frustrated translation of adsorbed NO in the excited state, in contrast to the frustrated rotation, in which softening occurs.2. Laser-induced desorption of NO from the surface of a Pt (111)-Ge surface alloy, while CO is not desorbed. The elctronic structure of the alloy and the electronic state of CO adsorbed on this surface were observed by photoelectron spectroscopy. The band width of the alloy is narrower than that of Pt. This result is reasonable. The binding energy of the CO 5sigma state on the alloy is nearly equal to that on Pt (111), while the desorption energy is quite different. This contradictory result can be interpreted by a perturbation model.3. The 1 monolayr Ge surface on the Pt (111)-Ge surface alloy. The insulator-metal transition on the Ge overlayr was observed by reflection absorption infrared spectroscopy.The band width of the absorption spectrum for C-O stretching vibration of adsorbed CO becomes much broader than that on Pt (111), Pt(111)-Ge and multilayr Ge.