Position-velocity diagrams across the two nuclei for the HCO⁺3−2 transition. The direction of each cut is shown by blue arrows in Fig. 2. The high-velocity emission extending up to above 500 km s^-1 corresponds to the vibrational emission of HCN (Fig. 3). Red lines show the V_sys of the entire system and the position of the nuclei. Toward the EN, the green line shows the derived velocity of the nucleus V_EN − V_sys ~ 117 km s^-1.