Time-Resolved Observation of the Solvation Dynamics of a Rydberg Excited Molecule Deposited on an Argon Cluster. II. DABCO☆ at Long Time Delays.

The real-time dynamics of DABCO-argon clusters is investigated in a femtosecond pump-probe experiment where the pump excites DABCO to the S1 state within the argon cluster. The probe operates by photoionization and documents the energy and angular distributions of the resulting photoelectrons. The present work complements a previous work from our group [Awali Phys. Chem. Chem. Phys., 2014, 16, 516-526] where this dynamics was probed at short time, up to 4 ps after the pump pulse. Here, the dynamics is followed up to 500 ps. A multiscale dynamics is observed. It includes a jump between two solvation sites (time scale 0.27 ps) followed by the relaxation of the solvation cage excess vibrational energy (time scale 14 ps) and then by that of DABCO (time scale >150 ps). Polarization anisotropy, double polarization, and angular anisotropy effects are reported also. They are interpreted (quantitatively for the former effect) in terms of decoherence of rotational alignment, driven by the overall rotation of the DABCO-argon clusters. A tomographic view of the DABCO excited orbital, provided by the double anisotropy effect, is discussed on a qualitative basis.