Observed (black) and synthetic (red) spectra of the five transitions of (CH₂OH)₂ in W51/e2 that are used for the analysis. Also shown are the synthetic spectra of all other species investigated in this study (blue) to demonstrate that the (CH₂OH)₂ lines in question are not blended. The transitions are located at 239 883.56, 240 807.88, 242 656.23, 242 948.29 and 100 333.64 MHz – denoted by black vertical lines in the plot. The displayed frequency region in each plot corresponds to ~200 km s^-1.