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

1. Spectroscopic study of alkali-earth atom - He collision dynamics in low temperature(1) Formation of Mg^He_n exciplex in low temperatureWe have observed the formation of ^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_. We have also observed almost the same results for Mg_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_ 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.