| Abstract
| - We present results of classical trajectory calculations on the sticking of hydrogen atoms to the basal plane(0001) face of crystalline ice, Ih. The sticking probability is found to decrease with both incidence energy (Ei)and surface temperature (Ts). At the surface temperatures studied, the sticking probability can be fitted to asimple decay function: Ps = 1.5 e-Ei(K)/175 at Ts = 10 K, and Ps = 0.85 e-Ei(K)/175 at Ts = 70 K. In the trappedstate, the adsorbed hydrogen atom is located on top of the ice surface, over the center of a surface hexagonalring, interacting with all water molecules forming the ring. The calculated physisorption energy of the adsorbedatom is approximately 400 ± 50 K. The results of our calculations are compared with the experimental andtheoretical data for amorphous ice surfaces. At Ts = 10 K, our values for the sticking probability are higherthan those of Buch and Zhang [Buch, V.; Zhang, Q. Astrophys. J.1991, 379, 647], which is attributed todifferences in surface topology. Our sticking probability values are lower than those of Masuda et al. [Masuda,K.; Takahashi, J.; Mukai, T. Astron. Astrophys.1998, 330, 243], which we attribute to an incorrectimplementation of the H−H2O potential in their work. The experimental results available on hydrogen formationon amorphous ice are in good agreement with our results, if the assumption is made that all H-atoms thatstick will recombine. Our calculations then suggest that the formation of H2 through recombination of H-atomsadsorbed on the surface is efficient enough to compete with the cosmic destruction of H2.
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