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Two favourable computed structures of <i>N</i>-methylacetamide (NMA) trimer which have been overlooked in previous studies, because they are stabilized by London dispersion interactions in addition to NH...O=C hydrogen bonding. Structure optimization and harmonic spectra at B3LYP-D3(BJ)/aug-cc-pVTZ level confirm that these or similar structures are present in a supersonic jet expansion of NMA in helium which is probed by linear Raman spectroscopy, together with dimers and larger clusters.<br><br>The calculations were carried out with Gaussian09 E.01, the visualization with Gaussview 5.0.9, the figure was produced with Microsoft Powerpoint 2013.<br><br>The publication describing these calculations together with the experimental data is currently being prepared. <br>