The equilibrium geometry of linear C3O has been calculated with high precision (≈ 0.0005 Å accuracy) by combining experimental ground-state rotational constants and theoretical vibration-rotation coupling constants. The results are R1e (C1C2)=1.2717 Å, R2e(C2C3)=1.2965 Å and R3e(C3O)=1.1473 Å. New matrix IRspectra show a larger number of peaks not observed before which are assigned to overtones