GBT spectra of NH₃(1,1) and (2,2) obtained towards the sources classified as HMSCs. For each spectrum, the x-axis represents a velocity interval of ± 35 km s^-1 from the systemic velocity listed in Table 1. The y-axis shows the intensity scale in main beam brightness temperature units. In each spectrum, the red curve indicates the best fit either obtained by fitting the hyperfine structure, when possible, or with a single Gaussian (see Sect. 3.1).