Investigation of Ion−Molecule Reactions via Femtosecond Excitation and Ionization of [Tetrakis(dimethylamino)ethylene] n ≥ 1

The dynamics of ionic monomer and multimers of the ethylenic molecule TDMAE (tetrakis(dimethylamino)ethylene) have been studied under femtosecond stepwise excitation using an energy surface of the neutral molecule (or cluster) as a relay. This specific excitation takes advantage of the wave packet evolution in the neutral intermediate state to (i) allow access to different regions of the ionic potential surface and (ii) identify some aspects of the dynamics in the ionic state of either TDMAE+ or TDMAE n +. This original experimental approach we shall name double pump excitation. We have identified the existence of a double well in TDMAE n + corresponding to a different localization of the positive charge, the most stable corresponding to a complete delocalization over the nitrogen atoms. A reaction in the dimer and higher multimer ions is observed that involves the formation of compounds of general mass 200 m 116 n +. This reaction is only observed in clusters and not in thermal ion molecule collisions between TDMAE+ and TDMAE. A tentative mechanism of formation for this product is proposed that involves the creation of a distonic ion via H-atom migrations. The double pump method could be extended to many other systems to explore competing pathways in ionic reactions, differently accessed via transient states of a neutral intermediate.