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Ortho-para conversion of hydrogen molecules at solid surfaces : elucidation of the mechanism and application to a new spin probe at surfaces

固体表面氢分子的邻位-对位转换：阐明其机制及其在表面新型自旋探针中的应用

基本信息

批准号：
10440086
负责人：
FUKUTANI Katsuyuki
金额：
$ 8.19万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 1999
项目状态：
已结题

项目摘要

Hydrogen molecules have internal degrees of freedom, nuclear spin and rotational motion, which are known to play an important role in the interaction with solid surfaces. The purpose of the present project is to elucidate the microscopic mechanism of the interaction difference between the ortho-and para-hydrogen with solid surfaces and the ortho-para conversion. In order to achieve this, we have developed a new experimental technique of rotational/spin-state selective thermal desorption spectroscopy by using resonance-enhanced multiphoton ionization, with which we have experimentally investigated the difference of the desorption energy between ortho- and para-hydrogen molecules and the ortho-para conversion rate at mesoporous alumina and copper surfaces. We have found the following results : 1. The desorption energy of hydrogen molecules at meso-pores of alumina is higher than that at particle surfaces, 2. The ortho-para conversion time is 32 min at meso-pores, 3. The ortho-para conversion time at particle surfaces is shorter than 7 min, 4. The desorption energy of the ortho-hydrogen is higher than that of para-hydrogen by about 6 meV. The ortho-para conversion is considered to be driven by the magnetic dipole interaction with impurity spins at surfaces. The difference of the desorption energy between ortho- and para-hydrogen is concluded to originate from the anisotropy of the adsorption potential at these surfaces.

氢分子具有内部自由度、核自旋和旋转运动，已知这些在与固体表面的相互作用中发挥着重要作用。本项目的目的是阐明邻氢和仲氢与固体表面相互作用差异以及邻氢转化的微观机制。为了实现这一目标，我们开发了一种利用共振增强多光子电离的旋转/自旋态选择性热脱附光谱的新实验技术，通过实验研究了邻位和仲位氢分子之间的解吸能差异以及介孔氧化铝和铜表面的邻位-对位转化率。我们发现以下结果： 1. 氧化铝介孔处氢分子的解吸能高于颗粒表面的解吸能； 2. 介孔处的邻对位转化时间为 32 min； 3. 颗粒表面的邻位对位转化时间小于 7 min； 4. 邻位氢的解吸能高于仲位氢。约 6 meV。邻位-对位转换被认为是由磁偶极子与表面杂质自旋的相互作用驱动的。邻氢和仲氢之间解吸能的差异被认为是源于这些表面吸附势的各向异性。