Deuterium enhancement of monodeuterated species has been recognized for more than 30 years as a result of chemical fractionation that results from the difference in zero-point energies of deuterated and hydrogenated molecules. The key reaction is the deuteron exchange in the reaction between HD, the reservoir of deuterium in dark interstellar clouds, and the
molecular ion, leading to the production of H
2
D
+
molecule, and the low temperature in dark interstellar clouds favours this production. Furthermore, the presence of multiply deuterated species have incited our group to proceed further and consider the subsequent reaction of H
2
D
+
with HD, leading to D
2
H
+
, which can further react with HD to produce
. In pre-stellar cores, where CO was found to be depleted, this production should be increased as CO would normally destroy
. The first model including D
2
H
+
and
predicted that these molecules should be as abundant as H
2
D
+
. The first detection of the D
2
H
+
was made possible by the recent laboratory measurement for the frequency of the fundamental line of
para
-D
2
H
+
. Here, we present observations of H
2
D
+
and D
2
H
+
towards a sample of dark clouds and pre-stellar cores and show how the distribution of
ortho
-H
2
D
+
(1
1,0
–1
1,1
) can trace the deuterium factory in pre-stellar cores. We also present how future instrumentation will improve our knowledge concerning the deuterium enhancement of
.
On the fundamental line of galactic and extragalactic globular clusters
