  Dissociative electron attachment (DEA) is one of the processes that shows a
strong coupling between the nuclear and electronic degrees of freedom in a
molecule. This coupling results in an efficient transformation of the kinetic
energy of attaching free electrons into the chemical energy of the compound
molecule. A recent discovery of quantum coherence in this process has opened a
whole new dimension in its description. On the other hand, the mass variation
in isotopes of the constituent atoms has a profound effect on DEA. In quantum
coherence observed in DEA, the isotope effect depicts itself in terms of change
in the phase and the amplitude of the interfering dissociation paths. Here, we
report the quantum coherence observed in DEA to HD, an isotopologue of H$_2$.
In this isotopologue, both H$^-$ and D$^-$ show identical forward-backward
asymmetry in the angular distribution. We explain these findings using the
interference between two quantum paths, with the permanent dipole moment of the
asymmetric mass playing no role in the process.
