抄録
The isotope enrichment by the formation of neutral and ionic clusters is discussed. In the free jet expansion, the heavier isotopes are enriched in the neutral clusters and the lighter isotopes are preferentially eliminated from the neutral clusters. In the free jet seeded with ions, the enrichment of heavier isotopes in the ionic clusters is greatly enhanced compared to that in the neutral clusters. This is mainly due to the large zero-point energy difference in the bond energies between the neutral and ionic clusters. The enrichment factor for ionic clusters decreases with the growth of cluster size and converges to that for the neutral ones. The deuteron-held heavy hydrogen clusters D3+(D2)n are found to be thermochemically more stable than the proton-held hydrogen clusters H3+(H2)n with n=2~9. This is due to the tighter bond formation with n≤6 and to the more favorable entropy effect with n=7~9 for the clusters D3+(D2)n.
