Investigation on the quantum motion of H on transition metal surfaces

H是最轻的元素，因此H的运动通常不是用经典的而是用量子力学来描述。对于H在金属表面上，表面扩散的活化能几乎与H的振动能是相同的量级。因此，振动激发态的H可以被预期是量子的，电子在机械上离域，因此振动能级由原子带模型描述，就像周期性势阱（布洛赫态）中的电子一样。理论计算表明，H在Ni表面上的振动激发能级的宽度为几个。用高分辨电子能量损失谱（HREELS）研究了90 K下Hon Pd（110），Ni（111）和Rh（111）的振动光谱。对于Pd（110）表面上的H，在87-89，96-100和121-122 meV的低H覆盖区观察到三种损失。将87-89和96-100 meV能量损失的覆盖度依赖性与基于H量子离域的模型计算结果进行了比较，实验结果与理论结果符合得相当好，由此得出结论：处于振动态的H在Pd（110）上是量子力学离域的。本文研究了HNi（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，这些伸缩模的能量损失范围很窄（约2 meV）.随着H覆盖度的减小，在60 - 110 meV范围内观察到了弱而宽的结构，这可能与H的量子动力学有关。对于Rh（111）上的H，EELS谱没有显示出任何H量子离域的证据，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.