Abstract Spectra of the van der Waals trimers Ar2–N2O and Ne2–N2O are studied in the region of the N2O ν1 fundamental (≈2220 cm−1) using a tunable quantum cascade laser to probe a pulsed supersonic expansion from a slit jet nozzle. Improved data are obtained for the dimers Ar–N2O and Ne–N2O, and the Q-branch of Ar3–N2O is tentatively assigned. The vibrational shifts for Nen–N2O are almost exactly linear for n = 0–2. However, for Arn–N2O the n = 2 band origin is slightly blue-shifted compared to the linear prediction, and the n = 3 origin (if correct) is more significantly blue-shifted (by 0.09 cm−1).