Hanning-smoothed spectra towards G1.87−SMM 1. The single-Gaussian and hf structure fits are shown with green lines. The vertical red line plotted on double-peaked profiles indicates the radial velocity of the optically thin HC₃N line. The velocity range is wider in the C₂H and HCO⁺ (line emission peak) spectra than in the other panels to show all the detected lines (the additional velocity component is included for the latter).