Mean spectra of the N₂H⁺ (top) and C¹⁸O (bottom) molecular lines from the 30m datasets for L1448-2A. The best fits of the spectra, by a hyperfine structure and a Gaussian line profile models respectively, are represented in green solid lines. Top panel: the velocity axis corresponds to the isolated HFS component 1₀₁ − 0₁₂. The systemic velocity is estimated to be 4.10 km s⁻¹ for this source (see Table E.1).