Spectrum obtained toward Sgr B2(M) in the 3 mm window with the IRAM 30 m telescope in main-beam temperature scale. The synthetic model is overlaid in green and its relevant lines are labeled in blue. The frequencies of the hydrogen and helium recombination lines are indicated with a pink label. The position of the lines with a peak temperature higher than 2 K in the image band and possibly contaminating the spectrum are marked with a red label indicating their rest frequency and their peak temperature in K in the image band.