| Popis: |
Present evidence for where and in what forms the abundant elements O, C, N, Si, Mg, Fe, and S occur in molecular clouds is reviewed. Studies of both gas and dust show that most of the elements, with the probable exception of N, are far below cosmic abundances in the gas and must be sequestered in dust. This can strongly affect molecular cloud chemistry, especially in active regions. Most of the Si, Mg, and Fe appear to be in refractory minerals, perhaps mainly as oxides. Oxygen and carbon exist in both refractory compounds and volatile ices. Several lines of evidence point to complex, solid carbon compounds in the dust, but they are still incompletely specified. Significant fraction of O and C in molecular clouds are still unaccounted for. |
