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

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

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

Keggin heteropolyacid H3PW12O40 supported on different oxides for catalytic and catalytic photo-assisted propene hydration

Catalytic and catalytic photo-assisted hydration of propene to form 2-propanol in gas–solid regime at atmospheric pressure and 85 1C were carried out by using a heteropolyacid (POM) supported on different oxides. Binary materials were prepared by impregnation of H3PW12O40 on different commercial and home prepared supports (TiO2, SiO2, WO3, ZrO2, ZnO, Al2O3). Some of the composites were active both for catalytic and catalytic photo-assisted reactions. The Keggin type POM was completely and partially degraded, when supported on ZnO and Al2O3, respectively, and these binary solids always resulted as inactive for both catalytic and catalytic photo-assisted reactions. The supported Keggin POM species played a key role both for the catalytic and the photo-assisted catalytic reactions, due to their strong acidity and ability to form strong oxidant species under UV irradiation, respectively. The contemporary presence of heat and UV light improved the activity of almost all POM supported materials. All materials were characterized by X-ray diffraction (XRD), scanning electron microscopy observations (SEM), diffuse reflectance spectroscopy (DRS), determination of the conduction and valence band energy by photovoltage measurements, Fourier transform infrared spectroscopy (FTIR), NH3-TPD experiments and time resolved microwave conductivity (TRMC). Introduction Propene hydration to obtain 2-propanol is a reaction carried out at moderate temperatures (ca. 150–200 1C) and pressure (2MPa) in the presence of an acid catalyst;1 however the realization of this reaction at ambient conditions is of great interest. The us

Solvation shift of a conical intersection in clusters of excited tetrakis(dimethyl amino)ethylene with ammonia and acetonitrile molecules

A supersonic expansion of the title molecule (TDMAE) with helium and polar solvent molecules S (ammonia or acetonitrile) generates TDAME(S)10 clusters. By applying the femtosecond pump–probe technique, a wavepacket is launched on the S1 potential energy surface of TDMAE. The electronic configuration of TDMAE changes from valence V(ππ*) to Zwitterionic C+C− when the wavepacket passes in the vicinity of a conical intersection. While argon as solvent slows down this switch by an inertial effect, the present polar molecules move the conical intersection, reduce the length of the way to access it and accelerate the corresponding V-to-Z energy transfer

Observation of doubly ionised metalloporphyrins in the gas phase prepared by femtosecond ionisation

Double ionisation of ruthenium–CO octaethyl porphyrin has been observed in the gas phase by femtosecond sequential 400/800 nm multi-photon excitation. Time resolved measurements show the important effect of femtosecond delayed two colour ionisation in producing efficiently doubly ionised metalloporphyrins. This is related to ultrafast electronic relaxation after the first 400 nm pump laser. The stability of such metallophyrin doubly charged ions is exceptional owing to the ability of the ring and the metal to accommodate two positive charges. These measurements relate to the positive charge distribution in the metalloporphyrin and should allow a detailed investigation of the redox properties of these important molecules