The lowest retention values of51Cr hot atom in various forms of the -diketonetype complexes, Cr(bzac)3, Cr(dpm)3 and Cr(dbm)3, as well as Cr(acac)3 as a reference, were obtained in the experimental condition in which they are regarded as the primary retentions. From these retention values, the threshold energies for producing a hot atom, the appearance energies, were estimated using the calculated relationship between the primary retention and appearance energy, which was obtained by the recoil energy spectra computed by the method recently developed by us. The appearance energy increased steeply with increasing molecular weight of the complex. A theoretical interpretation for this result was attempted by setting a model in which a hot atom is produced in the center of the complex and receives the stopping action by the surrounding ligand molecule. The agreement between the observed and calculated values was good.