IR spectra in the range 1300–900 cm⁻¹ of residues acquired after 30 min at 300 K. The spectra of the 1:1:1 + 29 eV/16 u and of the 3:1:1 + 67 eV/16 u residues are obtained after the smoothing of the acquired spectra (grey lines in the background). For comparison, we show the spectrum of a 1:1:0+85.2 eV/16 u residue. We do not show spectra between 1253 and 1274 cm⁻¹ because of the presence of spikes due to not well compensated water vapour. Vertical dashed lines show the positions of pure HMT bands reported by Bernstein et al. (1995). Black horizontal lines show the range of HMT and HMT-derivatives bands according to ab-initio calculations by Bera et al. (2019) and Materese et al. (2020).