We consider the effect of isotopic labeling on the electric charge distribution and dynamics of the formic acid dimer. Our investigation is based on accurate ab initio calculations of vibrationally induced dipole moments and multidimensional quantum calculations of vibrational ground-state splittings. It is found that non-negligible dipole moments of mu = 0.032 D and mu = 0.021 D arise in HCOOH-DOOCD and HCOOH-DOOCH, respectively, suggesting the feasibility of microwave studies. Within the reaction surface Hamiltonian approach a ratio of splittings of 1:0.2:0.045 is predicted for HCOOH-HOOCH:HCOOH-DOOCH:HCOOD-DOOCH.