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Energy-gap-dependentvibrational-energy transfers among the nitrilestretches of KSCN/KS13CN/KS13C15Nin D2O, DMF, and formamide liquid solutions at room temperaturewere measured by the vibrational-energy-exchange method. The energytransfers are slower with a larger energy donor/acceptor gap, independentof the calculated instantaneous normal mode (“phonons”in liquids) densities or the terahertz absorption spectra. The energy-gapdependences of the nonresonant energy transfers cannot be describedby phonon compensation mechanisms with the assumption that phononsare the instantaneous normal modes of the liquids. Instead, the experimentalenergy-gap dependences can be quantitatively reproduced by the dephasingmechanism. A simple theoretical derivation shows that the fast molecularmotions in liquids randomize the modulations on the energy donor andacceptor by phonons and diminish the phonon compensation efficiencyon energy transfer. Estimations based on the theoretical derivationssuggest that, for most nonresonant intermolecular vibrational-energytransfers in liquids with energy gaps smaller than the thermal energy,the dephasing mechanism dominates the energy-transfer process. [ABSTRACT FROM AUTHOR]