COLLISIONAL FLOW OF VIBRATIONAL-ENERGY INTO SURROUNDING VIBRATIONAL FIELDS WITHIN S-1 P-DIFLUOROBENZENE - RATE CONSTANTS FOR INITIAL LEVELSWITH HIGH VIBRATIONAL-EXCITATION

State-to-field vibrational energy transfer from optically pumped vibra tional levels in S-1 pDFB by single collisions with Ar at 300 K has be en characterized for 18 initial levels whose energies range from 0 to about 2500 cm(-1) where the density of levels is about 200 per cm(-1). The rate constants vary according to the zero order identity of the i nitially pumped level, even for the highest levels that are of extensi vely mixed vibrational character. In the midst of these variations, th e constants gradually increase as higher energy levels are pumped, but the energy regime where the rate constants level off has apparently n ot yet been reached. The largest rate constants are about 60% of the L ennard-Jones value. Transfers involving single quantum changes in the lowest frequency mode, nu(30)' = 120 cm(-1), are the dominant single c hannels for all levels. These channels result in elevated rate constan ts for initial levels that contain quanta of nu(30)'. If the state-to- state nu(30)' contributions are subtracted from the state-to-field rat e constants, the entire set of rate constants has close similarity to that for benzene + CO over the same S-1 energy range. Attempts to mode l the state-to-field rate constants using propensity rules that descri be well many S-1 pDFB state-to-state transfers are only partially succ essful. The modeling shows, however, that increase of state-to-field r ate constants at higher energies is primarily a consequence of increas ing numbers of state-to-state channels that involve larger vibrational quantum number changes (Delta upsilon greater than or equal to 3).