Investigation on the quantum motion of H on transition metal surfaces

H是最轻的元素，因此H的运动通常用量子力学而不是经典的量子力学来描述，而对于金属表面的H，表面扩散的激活能几乎与H的振动能相同。因此，振动激发态中的H可以被认为是量子力学离域的，从而可以用原子能带模型来描述振动能级，就像周期势垒(Bloch态)中的电子一样。对Ni表面H的理论计算表明，振动激发能级的宽度很小。用高分辨电子能量损失谱(HREELS)研究了Hn Pd(110)，Ni(111)和Rh(111)在90K下的振动光谱。对于Pd(110)表面的H，在低H覆盖区，在87-、96-100和121-122 meV处观察到三个损失。87-89和96-100 meV损耗的覆盖率依赖关系与基于H的量子离域的模型计算结果相比较。实验结果与理论符合得很好，从而得出结论：振动态的H在Pd(110)面上是量子力学离域的。研究了H-Ni(111)的振动光谱，能量分辨率为1-2 meV。对于(2×2)-2H相，在90和96 meV处观察到H在hcp和fcc位的非对称伸缩模式。随着H覆盖率的降低，在60-110 meV范围内观察到了弱而宽的结构，这可能与量子基元H有关。对于Rh(111)上的H，EELS谱没有显示出H的量子离域，但能量分辨率不是很好(7-8 meV)，因此应该用更高的能量分辨率重新研究这个系统。

H is the lightest element and thus the motion of H is often described by not classical but quantu mechanics, As for H on metal surfaces, the activation energy of for surface diffusion is almost tr same order as the vibrational energy of H.Therefore, H in the vibrational excited states can be expected to be quantum-mechanically delocalized and thus the vibrational level is described by atomic band model just like an electron in the periodical potential well (Bloch state). The theo ret calculation for H on Ni surfaces indicates that the vibrational excited levels have widths of a few. several tens meV.We have investigated the vibrational spectra of Hon Pd(110), Ni(111) and Rh(111) at 90 K by using high resolution electron energy loss spectroscopy (HREELS). For H on Pd(110) surface, three losses are observed at 87-89, 96-100 and 121-122 meV for low H coverage regions. The coverage dependences of the 87-89 and 96-100 meV losses are compar with the model calculation based on the quantum delocalization of H.The agreement between experimental and theoretical results is reasonably good, and hence it is concluded that H in the vibrational state is quantum-mechanically delocalized on Pd(110). The vibrational spectra for H Ni(111) has been investigated with the energy resolution of 1-2 meV.For the (2x2)-2H phase, asymmetric stretching modes for H in hcp and fcc sites are observed at 90 and 96 meV.The wi of these losses are narrow (about 2 meV). As the H coverage is decreased, weak but broad structure ranging from 60 to 110 meV is observed which may be related to the quantum motior H.For H on Rh(111), EELS spectra do not show any evidence of the quantum delocalization of H However, energy resolution is not so good (7-8 meV) and thus this system should be reinvestigated with much high energy resolution.