Dissipation of translational energy of molecules on surfaces

2006年，我们利用超声波分子束装置和超高真空室进行了固体表面吸附物扩散实验。通过对阶梯状Pt（997）表面暴露于CO分子和随后暴露于能量受控的Ne或Ar原子后获得的傅立叶变换红外光谱的分析，获得了在平台位和台阶位吸附的CO扩散的活化能。利用碰撞诱导扩散理论，研究了吸附物在扩散过程中平动能的弛豫机制在Pt（997）表面暴露于覆盖度为0.033 ML的CO分子之后，其暴露于具有平移能的Ne或Ar原子。如果在平台位置处施加到CO分子的摩擦力低，则它们可以在碰撞赋予足够高的动能后迁移长距离。如果摩擦力很大，它们会在碰撞后立即停止。然后，摩擦力可以从CO分子与稀有气体原子碰撞后的分布来估计。然而，由于CO分子的平动能及其方向取决于CO分子和稀有气体原子碰撞时的排列，我们采用分子动力学计算，并将计算结果与实验结果进行了比较。根据比较，CO在Pt表面上的摩擦系数估计为8 × 10 - <12>4秒-1<-1>。

In 2006, we have performed the experiment about the adsorbate diffusion on solid surfaces by using super sonic molecular beam apparatus combined with ultra high vacuum chamber. From the analysis of the Fourier transformed infrared spectra obtained after a stepped Pt(997) surface was exposed to CO molecules and subsequently to energy-controlled Ne or Ar atoms, the activation energy of the diffusion of CO adsorbed at terrace site and step site were obtained.In 2007, we examined the mechanism of the relaxation of the translational energy of adsorbates on surfaces during the diffusion process by the use of collision induced diffusion phenomena as follows: After a Pt(997) surface was exposed to CO molecules with a coverage of 0.033 ML, it was exposed to Ne or Ar atoms with a translational energy. If the friction applied to CO molecules at terrace site is low, they can migrate long distances after a collision imparts a sufficiently high kinetic energy. If the friction is large, they will stop immediately after the collision. Then, the friction can be estimated from the distribution of CO molecules after the collision with rare gas atoms. However, since the translational energy of CO molecule and its direction depend on the arrangement of the CO molecule and the rare gas atom upon the collision, we employed molecular dynamics calculation and the calculational results were compared with experimental results. From the comparison, the friction coefficient of CO on the Pt surface was estimated to be 8x10^<12> sec^<-1>.