To gain insight into the possible magnitude of vibrational activation/deactivation rate constants for large molecules with the high vibrational excitation of thermal unmolecular reactions, absolute vibrational relaxation rate constants have been measured in S-1 p-difluorobenzene energy regions where the vibrational levels begin to form a quasi-continuum. The measured rate constants define vibrational energy transfer from three initially pumped S-1 levels into the surrounding vibrational Field. The observed rate constants are about 60% of the Lennard-Jones value for the collision partner Ar and about 40% for lie. The initial levels lie in the epsilon(vib) range 2887 to 3310 cm(-1), where the level densities are approximately 800-2000 per cm(-1). New He rate constants are also measured for many lower initial levels. When combined with earlier measurements, the He and At rate constants span the range 0 less than or equal to epsilon(vib) less than or equal to 3310 cm(-1). Both sets of rate constants show a trend to larger values with increasing epsilon(vib) and have prominent variations in response to the zero order quantum identity of the initial level. When the high level density starts to create overlapping states, the Ar rate constants for the three highest levels appear to have leveled off, and the initial quantum state variations are damped out. The He rate constants, on the other hand, sustain the trend to larger values even at the highest energies where the data are ambiguous on whether initial quantum state sensitivity persists.