Ultra-High-Resolution Spectroscopy of Solid Hydrogen

固体对氢是一种很有前途的高分辨光谱介质。由于分子间的弱相互作用，氢分子和嵌入固体中的分子的旋转激发态和振动激发态被很好地量子化。此外，由于内部运动与晶体声子之间的能量失配，激发态的寿命变得非常长，使得谱线宽度窄至1MHz。本研究的目的是开发一种以固体对氢为介质的凝聚相超高分辨率光谱新技术，以便更详细地阐明分子的旋转运动和分子间的多体相互作用。在研究项目期间，我们获得了以下新成果。(1)利用高分辨率红外光谱对准氢分子和准氢晶体中杂质对的纯振动跃迁进行了分析，定量获得了激子跳变和分子间相互作用的信息。(2)我们发现在准氢晶体中掺杂的分子也表现出量子化的旋转振动态。高分辨率的红外光谱为凝聚态分子的旋转振动运动分析提供了新的理论。(3)利用红外光谱首次观察到几种纯隧穿化学反应。(4)我们开发了一种在固体中产生分子离子的技术，使我们能够在高分辨率下研究化学感兴趣的氢离子。

Solid parahydrogen is a promising medium for high resolution spectroscopy. The rotational and vibrational excited states of hydrogen molecules and molecules embedded in the solid are well quantized on account of the weak intermolecular interaction. Moreover, due to the energy mismatch between the internal motion and the crystal phonon, the lifetime of the excited states becomes enormously long so that the spectral linewidth becomes as narrow as 1MHz. The purpose of the present research is to develop a new technique of ultra-high-resolution spectroscopy of condensed phase using solid parahydrogen as a medium in order to clarify rovibarional motion of molecules as well as intermolecular many-body interactions in condensed phase in great detail. We obtained the following new results during the period of the research project.(1) High-resolution infrared spectroscopy of pure vibrational transitions of parahydrogen molecules and impurity ortho-hydrogen pairs in parahydrogen crystals was performed to obtain information on exciton hopping and intermolecular interaction quantitatively.(2) We found that molecules doped in parahydrogen crystal also show quantizedrotation-vibration states. The well-resolved infrared spectrum allows us to develop new theory for the analysis of rovibrational motion of molecules in condensed phase.(3) Several pure tunneling chemical reactions were observed for the first time by infrared spectroscopy.(4) We have developed a technique toproduce molecular ions in the solid which allows us to study hydrogenic ions of chemical interests under high-resolution.