Laser spectroscopic study of formation of alkali-earth and He van der Waals molecules

1. 低温下碱土原子-氦碰撞动力学的光谱研究(1)低温下Mg^<*4>He_n杂合体的形成我们在低温He气体（5-30K）中，用激光激发Mg进入3s3p ^1P_1态，观察到Mg^<*4> MgHe_n杂合体的形成。用理论对势分析了发射光谱。杂合体在其电子激发态的生命周期内在许多三体反应中生长。最后，多达10个He原子附着在一个Mg原子周围，形成Mg*He_<10>。我们也在Mg_<-3>He碰撞中观察到几乎相同的结果。在本研究中，我们发现尽管Mg和He之间的吸引相互作用能很小，但Mg*Hen分子仍能形成。(2) Ba^<+>-He的碰撞动力学我们用激光光谱法研究了Ba+在6p ^2P_<3/2>态与He原子碰撞时的弛豫过程。我们得到了Ba+*He的形成和解离速率常数，以及Ba+和Ba+*He的精细结构变化碰撞。在Ba+*He外络合物形成的截面上观察到的类共振结构表明两步Lindemann机制。我们还观察到在低温下精细结构变化碰撞的横截面有特殊的增加。这表明低温下开启了细结构变化的另一条通道。测定了碱土离子在室温下与He、H_2和D_2碰撞时的精细结构变化截面。我们发现He原子碰撞的横截面随着精细结构的分裂呈指数减小，这可以用绝热跃迁的Landau-Zener模型来解释。与此相反，由于精细结构分裂与氢分子旋转之间的共振，氢分子的横截面大大扩大。

1. Spectroscopic study of alkali-earth atom - He collision dynamics in low temperature(1) Formation of Mg^<*4>He_n exciplex in low temperatureWe have observed the formation of ^<*4>MgHe_n exciplexes by means of laser excitation of Mg into the 3s3p ^1P_1 state in low temperature He gas (5-30K). Emission spectra have been analyzed using a theoretical pair potential. Exciplexes grow in many three-body reactions within its lifetime in the electronic excited state. Finally up to ten He atoms are attached around to a Mg atom to form a Mg*He_<10>. We have also observed almost the same results for Mg_<-3>He collisions. In this research, we have shown that the Mg*Hen molecules are formed although attractive interaction energy between Mg and He is small.(2) Collision dynamics of Ba^<+>-HeWe have investigated the relaxation process of Ba+ in the 6p ^2P_<3/2> state in collision with He atoms using laser spectroscopic method. We have obtained the rate constants of the formation and dissociation of Ba+*He, and the fine structure changing collision of Ba+ and Ba+*He. The resonance like structure observed in the cross section of the formation of Ba+*He exciplex indicates the two-step Lindemann mechanism. We have also observed a peculiar increase in the cross section of the fine-structure changing collision at the low temperature. This indicates another channel of the fine-structure change opens in the low temperature.2. Fine-structure changing collision of alkali-earth ionWe have measured the fine-structure changing collision cross sections of alkali-earth ions at room temperature in collision with He, H_2 and D_2. We have found that cross sections for collisions with He atoms decrease exponentially with the fine-structure splitting, which can be explained by the Landau-Zener model of the adiabatic transition. In contrast to this, cross sections for hydrogen molecules are much enlarged due to resonance between the fine-structure splitting and the rotation of hydrogen molecule.