Comment on ‘‘The weakest bond: Experimental observation of helium dimer’’ [J. Chem. Phys. 9 8, 3564 (1993)]

Recently, Luo et al. reported indirect evidence for the formation of dimers in a supersonic expansion of helium. They interpreted their data as confirmation of the existence of a bound state of 4He–4He with a binding energy of order 1 mK. We show that their data are actually consistent with the formation of helium trimers and not dimers. The two control experiments that they performed do not provide any evidence for discarding this alternative hypothesis.