Femtosecond photodissociation dynamics of van der Waals cationic clusters: a tool for detecting metastable isomers of organic cations

A femtosecond pump (266 nm)–probe (800 nm) experiment as been performed on small clusters of tetrakis(dimethylamino)ethylene (TDMAE) with argon (TDMAE(Ar)≪10). The pump excites TDMAE and initiates deformations of the molecule within the cluster. Then, the probe ionises TDMAE and disposes enough excess energy in the cluster to evaporate all argon atoms. However, ionisation during the first 150 fs after the pump gives preferentially access to a metastable configuration of the TDMAE+ ion, unquenched by the argon environment. This takes up enough of the excess energy to prevent complete argon evaporation. Observing the non-total-evaporation of weakly bond clusters formed of an organic cation with argon appears as a useful tool to reveal the existence of such metastable configurations in organic cations.