The evolution of charged particles in a model of contracting cloud

The evolution of charged particles is followed during contraction of a model of an interstellar cloud, with initial density number of n = 10/cu cm. The contraction is followed up to a density increase of 5 orders of magnitude. Special care is given to the details of the negative ions. In addition, we have tested the ambipolar diffusion according to results of the ion density. The results predict the importance of atomic ions in the diffuse regions. H(+) and C(+) are distinctly enhanced in the beginning of contraction but decrease as contraction proceeds. Molecular ions enhance as contraction proceeds and becomes important in dense regions. The most enhanced molecular ions are HCO(+), O2(+), C2H3(+), H3O(+) and SO(+). H3(+) is less abundant. The atomic ions (except metallic ions) decrease noticeably as density increases. In general, the negative ions are of negligible fractional abundances. The time of ambipolar diffusion is shorter than the dynamical time, hence the magnetic field should be weakened in the central core as the central density increases to n = 10 exp 4/cu cm. (Author)