Abstract : RuO 4 is a heavy tetrahedral molecule of interest in several fields. Due to its chemical toxicity and radiological impact of its 103 and 106 isotopologues, the possible remote sensing of this compound in the atmosphere has renewed interest in its spectroscopic properties. We investigate here, for the first time at high resolution, the bending modes region in the far infrared. High resolution FTIR spectra have been recorded near room temperature, using a specially designed cell and an isotopically pure sample of 102 RuO 4. New assignments and effective Hamiltonian parameter fits for the main isotopologue (102 RuO 4) have been performed, treating the whole ν 2 /ν 4 bending mode dyad. We provide precise effective Hamiltonian parameters, including band centers and Coriolis interaction parameters.