Experimental Approach to Physicochemical Hydrogen Processes on Cosmic Ice Dust

Hydrogen is the most abundant element in the universe, and thus atomic and molecular hydrogen play important roles in chemical evolution in space. In particular, the physicochemical processes of hydrogen on cosmic dust, such as the diffusion of H atoms and nuclear spin conversion of H-2 molecules at low temperatures, are recognized to significantly influence the subsequent chemical evolution. However, it is not easy to track the hydrogen on the surface by conventional experiments. We have recently succeeded in applying a combination of photostimulated desorption and resonance-enhanced multiphoton ionization methods to detect hydrogen on cosmic dust analogues. In this paper, we present a brief review of our recent experiments for elucidating the behavior of hydrogen on water ice, pure solid carbon monoxide, and diamond-like carbon as cosmic dust analogue surfaces.