CN N=2 → 1 spectrum (black) and Gaussian fits (green) of NGC 253 in units of main beam brightness temperature on a LSR V_LSR = 0 km s^-1 frequency scale. The profile has been smoothed to a channel spacing of ~2.1 km s^-1 (1.5625 MHz). Numbers at the foot of each spectral feature provide expected relative intensities with respect to the weakest group of lines in case of optically thin emission under conditions of local thermodynamical equilibrium.