Averaging of the observations performed in the 216 GHz bandwidth. The ¹³CO(2–1) and C¹⁸O(2–1) lines present in this bandwidth are indicated in the rest-frame frequency of the Andromeda galaxy. For each line, the redshifted and blueshifted parts of the expected velocity range are indicated. The noise level achieved is 3 mK for a frequency binning Δν = 7 MHz (Δv = 9.5 km s^-1). Apart from the multiple-component ¹³CO(2–1) signal, the C¹⁸O(2–1) signal is weak in the receding part of the spectra.