Dynamics of excited tetrakis(dimethyl amino)ethylene solvated by argon atoms

S. Sorgues (1) , J.-M. Mestdagh (2) , B. Soep (2) , J. P. Visticot (2)

1 LCPO - Laboratoire de Chimie Physique D'Orsay
2 LFP - URA 2453 - Laboratoire Francis PERRIN

The supersonic expansion of a mixture of the title molecule (TDMAE) with argon generates a beam carrying a log-normal distribution of TDAME(Ar)n clusters, broadly centered at . The femtosecond pump–probe technique is used to investigate the excited state dynamics of these clusters up to a 220 ps delay between the pump and the probe. This documents the effect of the argon environment on the TDMAE dynamics. The TDMAE molecule is excited in the valence state V within the cluster by the pump laser at 266 nm. It undergoes deformation in the excited potential energy surface that brings the initial wavepacket to a conical intersection (CI), where the electronic configuration of the molecule switches to a zwitterionic configuration Z. Compared to the behaviour of free TDMAE, the effect of the argon environment is a slow down of the wavepacket movement and an increase of the time scale of the V–Z energy transfer from 300 to 400±50 fs. This slow down effect, that we call a chistera effect, differs from a standard cage effect. Here, the deforming molecule does not experience a hard sphere collision with the argon cage, rather it pushes it away. Furthermore, umbrella oscillations of the dimethylamino groups are excited when the initial wavepacket passes the CI region. Because of the argon environment, the sharp 250 fs oscillation period of the free molecules is transformed into a broad structure of 40 fs width (FWHM) centred at about 240 fs. In addition, breathing oscillations of the argon environment with respect to the TDMAE molecule are observed with a period of 410±40 fs. Finally, long delays between the pump and the probe lasers allow us to investigate the nonradiative energy transfer from the Z electronic configuration of TDMAE(Ar)n to a charge transfer state. The effect of the evaporation of argon atoms in the neutral and the ionised clusters has been taken into account, as its time scale accompanies that of the observed phenomena.

Domaines: Chimie théorique et/ou physique

S. Sorgues, J.-M. Mestdagh, B. Soep, J. P. Visticot. Dynamics of excited tetrakis(dimethyl amino)ethylene solvated by argon atoms. Chemical Physics, 2004, 301, pp.225-237. ⟨10.1016/j.chemphys.2004.03.001⟩. ⟨hal-00085085⟩