Knowledge Bank

State-to-field vibrational energy transfer (VET) from several high levels $(Evib>2800cm-1)$ within the $S1(1B2u)$ manifold of para-difluorobenzene (pDF) vapor at 300 K in single collisions with Ar and He is probed. A laser pump-dispersed fluorescence probe approach provides absolute collision cross sections for this large molecule (30 modes) in a region where the vibrational state density approaches 1$0-1$ per $cm-1$. In this region, pDFB is beginning to acquire the characteristics typical of high energy thermal unimolecular reactions, namely an enormous state density and highly mixed vibrational identities. Additionally, we have developed a technique based on electronic state quenching using molecular oxygen (chemical $timing)a$ by which we may investigate the behavior of the cross section as the mixed character of the pumped level is deliberately tuned. Tuning the vibrational character of the pumped level for a series of VET interactions provides the unique view of how (or whether) quantal effects influence VET in regions of large state density.