Rotational transitions of DCO+ in vibrationally excited states were measured in the region 360-440 GHz. The states investigated are: 0 2 0 (with l=0,2), 0 3 0 (with l=1,3), 0 4 0 (with l=0,2,4), 0 1(1) 1, and 1 0(0) 0. This study allowed us to carefully analyze the vibrational interaction affecting the first C-D stretching state 1 0(0) 0, which was confirmed to be due to the 0 1(1) 1 state. Taking account of the perturbation effect on the rotational constants of the involved states allowed to derive an accurate equilibrium structure of HCO+, which resulted to be r(CH)=1.092 04 A and r(CO)=1.105 58 A. (C) 2003 American Institute of Physics.