Interstellar deuterium in cold dense clouds

Abstract

The mechanism for deuterium fractionation in interstellar clouds is considered within the boundaries of the theory of Dalgarno and Lepp (1984). The abundance of D atoms and fractional ionization in cold clouds are derived from the observational data of molecular ions. It is shown that the abundance of atomic deuterium inside cold dense clouds should always be less than half the abundance of HD. In the five clouds considered, the upper limits of fractional abundance of D lie between 3.0 x 10 exp -7 and 1.9 x 10 exp -6. The upper limits of fractional ionization in cold clouds are found to be at least 3 times lower than previous estimates, and in the given clouds they range from 1.4 x 10 exp -7 to 4.3 x 10 exp -7. These upper limits of fractional ionization are independent of the assumed value of the cosmic deuterium-hydrogen abundance ratio (D)/(H).