Spectroscopic Study of Reaction Dynamics in Quantum Solids.

固体氢，被称为量子晶体，显示出极窄的谱线宽度，这使得我们能够通过高分辨率光谱研究嵌入在固体中的分子的相互作用和动力学。为了研究分子动力学中的量子效应，我们利用高分辨率旋转振动光谱研究了嵌套在固体对氢中的分子的激发态及其弛豫过程和化学反应性。我们得到的主要结果如下。(1)量子固体中电子激发态和振动激发态的松弛过程。我们发现嵌入在量子固体中的分子的振动激发态的纯消相具有T^4温度依赖性。在经典介质中，T^4温度依赖关系与T^7温度依赖关系具有本质上的不同。我们还发现量子固体中的核自旋弛豫主要是由分子内核自旋相互作用和单声子晶格旋转相互作用引起的。(2)量子固体中的离子。为了研究量子固体中的离子，我们用伽马射线照射固体氢。辐照后的固体呈现出新的复杂光谱特征，谱线宽度极窄。这些光谱特征归因于固体中产生的离子电场诱导氢分子的跃迁。(3)隧穿反应的量子效应。利用红外光谱研究了固体氢中X+H_2→XH+H型隧穿反应。隧穿反应速率在很大程度上取决于反应物和生成物的零点振动。此外，反应速率很大程度上取决于反应物的振动量子数。

Solid hydrogen, known as a quantum crystal, shows extremely narrow spectral linewidths, which allow us to study interactions and dynamics of molecules imbedded in the solid by high-resolution spectroscopy. In order to study quantum effects on dynamics of molecules, we have investigated excited states and its relaxation processes, and chemical reactivities of molecules imbedded in solid parahydrogen using high-resolution rotation-vibration spectroscopy. Main results we obtained are as follows.(1) Relaxation processes of electronic and vibrational excited states in quantum solid.We found a T^4 temperature dependence of pure dephasing of vibrational excited states of molecules imbedded in the quantum solid. The T^4 temperature dependence is intrinsically different from the T^7 temperature dependence in classical medium. We also found that nuclear spin relaxation in the quantum solid is mainly caused by the intramolecular nuclear spin-rotation interaction and the one-phonon lattice rotation interaction.(2)Ions in quantum solid.In order to study ions in quantum solids, we irradiated solid hydrogen by gamma-ray. The irradiated solid showed new complicated spectral features with extremely narrow spectral linewidths. These spectral features are attributed to the transitions of hydrogen molecules induced by electric fields of ions produced in the solid.(3) Quantum effects on tunneling reaction.We have investigated X+H_2→XH+H type tunneling reaction in solid hydrogen by infrared spectroscopy. The tunneling reaction rate depends drastically on the zero-point vibration of reactants and products. Moreover, the rate depends significantly on the vibrational quantum number of reactants.