Comparison between single-dish IRAM 30-m spectra (upper panels) and Plateau de Bure interferometric spectra (lower panels). To compare properly both sets of spectra, PdB spectra have been convolved to the single-dish beam size of the corresponding transition. For the HCO⁺ 1→0, the HPBW of the convolving Gaussian is 27.0″× 27.2″ and for the C¹⁷O 1→0, 9.4″× 9.2″ (to obtain the same angular resolution of the 30-m C¹⁷O 2→1 line). The conversion factor between Jy and K is 7 K = 1 mJy/beam for HCO⁺ 1→0 and 5 K = 1 mJy/beam for C¹⁷O 1→0.