Knowledge Bank

State-to-state vibrational energy flow by collisions with Ar atoms has been mapped out for 7 levels with up to $818cm-1$ of vibrational energy in $S1$ paradifluorobenzene. The most efficient pathway for energy transfer involve changes in the lowest frequency node, $\nu 30$ (this is also a promoting mode for collision-free IVR). The energy flow is modelled well by propensity rules similar to those for benzene. Rate constants for energy flow into the entire vibrational field were measured for levels up to $2500cm-1$ where the state density is 200 states/$ cm^{-1}$. The rules model these rate constants well for initial levels below $1100cm-1$. The modelling falls for the higher levels possibly on account of extensive level mixing and IVR.