Direct Observation of Microscopic Solvation at the Surface of Clusters by Ultrafast Photoelectron Imaging

Abstract

We report on microscopic observation of solvation by argon atoms of excited states of an ethylenic-like molecule, TDMAE (tetrakis dimethylaminoethylene). Two experimental methods were used: gas phase dynamics for the observation of the evolution through excited states, matrix isolation spectroscopy for characterization of the initial states. Excited state dynamics was recorded after the molecule had been deposited on the surface of a large argon cluster (n approximately 100) by pick-up. The deposited cluster was characterized by mass spectrometry and by its shifted photoelectron spectrum. The time evolution of the system was visualized by femtosecond pump/probe velocity map imaging of photoelectrons. The time evolution of deposited TDMAE excited at 266 nm can be modeled via a modified three state model, as in the free molecule. The initially excited state is of valence character, and a Rydberg state mediates the passage to a zwitterionic configuration. The specific solvation of Rydberg states by the surface of the cluster was directly observed and is discussed. It represents the striking outcome of the present work. It is inferred that differently from the gas phase, solvated Rydberg states resulting from state mixing within a R(n/lambda) complex in the presence of the argon surface are reached. Solvation of these Rydberg states should be effective through interaction of the ion core of the excited molecules with the cluster.

One-Electron Pseudo-Potential Determination of Stable Isomers of the Li*Ar n Excited Clusters: Absorption Spectra

“…In a smaller part, the complete interpretation of the experimental spectra necessitates an available potential energy surface describing the interaction of the ground state and excited states of alkali atom with argon atoms to simulate accurately the alkali-argon clusters structures. In that direction where: (i) we can provide guidelines about structure for experimental works, particularly for the laser-Induced-Fluorescence studies of alkali deposited on argon clusters [32], (ii) we understand the evolution of electronic excited states with increasing excitation level, (iii) we possibly observe the transition between nonwetting and wetting situations, depending on cluster size and excitation level, and (IV) we understand the relationship between the absorption band behaviour of the cluster optical electron and the position of the nearest argon neighbours.…”

Time resolved observation of the solvation dynamics of a Rydberg excited molecule deposited on an argon cluster-I: DABCO☆at short times

“…Time resolved dynamics of a deposited molecular system on a rare gas cluster provides a complex signal, which is not possible to fully analyse in time and in photoelectron energy using our standard procedure 11 nor the standard chemometric procedures. 41 Therefore we use a statistical signal processing approach.…”

“…Then the interaction between a rare gas cluster and a molecule excited in a Rydberg state comes very close to that described above for Hg ···Ar. We examine here the fate of a system 1,4-diazabicyclo-[2,2,2]octane (DABCO), a compact molecule whose first excited state is of strong Rydberg character (the wave function is 90% Rydberg-3s 11 ), deposited on a Ar n cluster by following its relaxation dynamics after excitation [11][12][13] . The ground electronic state of the DABCO molecule is however a valence state in nature.…”

“…We examine here the fate of a system, 1,4-diazabicyclo-[2,2,2]octane (DABCO), a compact molecule whose first excited state is of strong Rydberg character (the wave function is 90% Rydberg-3s 11 ), deposited on an Ar n cluster by following its relaxation dynamics after excitation. [11][12][13] The ground electronic state of the DABCO molecule is however a valence state in nature. Hence, different solvation effects are expected when the molecule is promoted into the S 1 state.…”

Approche bayésienne pour la décomposition conjointe d’une séquence de spectres de photo-électrons

“…Un exemple particulièrement simple et informatif apparaît dans (Gloaguen et al, 2005) : plusieurs états électroniques interviennent après que la molécule de tétrakis (diméthylamino-éthylène) ait été excitée électroniquement par une impulsion laser, celle-ci peuple un état de valence V ; ce dernier relaxe en totalité vers un état de Rydberg R qui lui-même relaxe vers un état zwitterionique Z. L'expérience rapportée dans (Gloaguen et al, 2005) est très simple car le laser interroge uniquement ces trois états et ceux-ci conduisent à trois raies parfaitement individualisées dans le spectre de photo-électrons : on observe alors que la raie associée à R est un transitoire, peuplé au cours du temps par la décroissance de la raie V, se dépeuplant lui-même au profit de Z. Les travaux en cours en dynamique réactionnelle portent sur des situations plus complexes. Par exemple, (Poisson et al, 2008 ; considèrent des situations maintenant très courantes où, d'une part, le nombre et la position des raies pour chaque spectre ne sont pas connus et, d'autre part, ces paramètres ne sont pas constants au cours de la séquence (ils peuvent varier d'un spectre à l'autre). Par ailleurs, les raies sont larges et empiètent les unes sur les autres dans un contexte où le rapport signalsur-bruit est faible.…”