Knowledge Bank

Optical excitation of the $(v\prime =10)13\Sigma g+\leftarrow 13\Sigma a+$ transition of $Na2$ formed on a He cluster surface yields dispersed emission which can only be modeled by including significant contributions from all $(v\prime -10)$ lower vibrational levels of the excited electronic state. The process by which this vibrational energy is transferred from the excited dimer to the He nanodroplet has been characterized using state-selective time-correlated single photon counting. We have measured the onset of fluorescence arising from lower $v\prime$ levels upon excitation of various higher vibrational states and find that in all cases fluorescence begins in less than 250 ps. Along with the non-exponential nature of the distribution of level populations, this leads us to conclude that the vibrational energy is not transferred in a cascading process but rather by means of multiquanta jumps. Following the vibrational deexcitation, the dimer emits in the gas phase, having desorbed from the cluster surface.