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International audienceThe corrosion mechanisms by liquid aluminum of three industrial materials have been studied: unalloyed steel (UAS), and ferritic and modified pearlitic cast irons (FCI and PCI, respectively). The behavior of these materials when in contact with liquid aluminum is different. Aluminum diffuses deep into the UAS and forms intermetallic compounds with iron at the surface and in the steel matrix. At the surface, only Fe2Al5 and FeAl3 are found. In the matrix, FeAl2 also is formed in agreement with the equilibrium Fe-Al diagram. From the matrix to FeAl2, the Al content in the ferrite increases progressively until Al saturation is reached. At this step, black elongated precipitates (Al4C3 and/or graphite) appear. Graphite lamellas present in both FCI and PCI constitute an efficient barrier to the Al diffusion. The high silicon content of the FCI leads to the formation of a phase free from Al and saturated in Si. For the PCI, a thin layer rich in Al and Si, which is formed between the matrix and Fe2Al5, limits the diffusion of atoms. The effects of Cr and P added in the PCI also are discussed

Direct measurements of Single vibronic Level InterSystem Crossing (SLISC) have been performed on the fluorenone molecule in the gas phase, by time resolved photoelectron and photoion spectroscopy. Vibronic transitions above the S1 nπ* origin were excited in the 432-420 nm region and the decay of S1 and growth of T1(3)ππ* could be observed within a 10 ns time domain. The ionization potential is measured as 8.33 ± 0.04 eV. The energy of the first excited triplet state of fluorenone, T1 has been characterized directly at 18 640 ± 250 cm(-1). The internal conversion of S1 to S0 is found to amount to ∼15% of the population decay, thus ISC is the dominant electronic relaxation process. ISC, although favored by the S1(1)nπ*-T1(3)ππ* coupling scheme, is 3 orders of magnitude less efficient than in the similar molecule benzophenone. Thus, the planarity of the fluorenone molecule disfavors the exploration of the configuration space where surface crossings would create high ISC probability, which occurs in benzophenone through surface crossings. The time evolution of S1 fluorenone is well accounted for by the statistical decay of individual levels into a quasi-continuum of T1 vibronic levels.

This paper is a joint experimental and theoretical approach concerning a molecule deposited on a large argon cluster. The spectroscopy and the dynamics of the deposited molecule are measured using the photoelectron spectroscopy. The absorption spectrum of the deposited molecule shows two solvation sites populated in the ground state. The combined dynamics reveals that the population ratio of the two sites is reversed when the molecule is electronically excited. This work provides the timescale of the corresponding solvation dynamics. Theoretical calculation supports the interpretation. More generally, close examination of the short time dynamics (0-6 ps) of DABCO···Ar(n) gives insights into the ultrafast relaxation dynamics of molecules deposited at interfaces and provides hence the time scale for deposited molecules to adapt to their neighborhoods.

This experimental work focuses on the complex autoionization dynamics of Ar(2) clusters below the first ionization energy of the argon atom. Ar(2) is submitted to vacuum ultraviolet radiation, and the photoelectron spectra are collected in coincidence with the cluster ions. The ionization dynamics is revealed by the dependence on the photon energy. We applied a new experimental method which we developed to analyze the photoelectron signal. Thus, we were able (i) to get the complete vibrational progression of Ar(2)(+) that was never observed up to now, especially identifying the 0-0 transition overcoming the usual Franck-Condon limitations during single photoionization, and (ii) to obtain the projections of the vibrational wave functions of the autoionizing states over the Ar(2)(+) functions. This method provides a powerful tool to test the potential energy curves computed by high level theoretical calculations on Rydberg states.

Probes of spin conservation in heavy metal reactions: Experimental and theoretical studies of the reactions of Re + with H 2 , D 2 , and HD

The real-time dynamics of DABCO-argon clusters is investigated in a femtosecond pump-probe experiment where the pump excites DABCO to the S 1 state within the argon cluster. The probe operates by photoionization and documents the energy and angular distributions of the resulting photoelectrons. The present work complements 1 a former one of our group [Awali et al., Phys. Chem. Chem. Phys., 2014, 16, 516-526] where this dynamics was probed at short time, up to 4 ps after the pump pulse.Here, the dynamics is followed up to 500 ps. A multiscale dynamics is observed.It includes a jump between two solvation sites (timescale 0.27 ps) followed by the relaxation of the solvation cage excess vibrational energy (timescale 14 ps) and then by that of DABCO (timescale >150 ps). Polarization anisotropy, double polarization and angular anisotropy effects are reported also. They are interpreted (quantitatively for the former effect) in terms of decoherence of rotational alignment, driven by the overall rotation of the DABCO-argon clusters. A tomographic view of the DABCO excited orbital, provided by the double anisotropy effect, is discussed on a qualitative basis.

The cluster isolated chemical reaction (CICR) technique was applied to neon clusters (Ne≈7000) on which barium atoms and methane molecules were deposited. Clusters carrying barium only were studied first. Qualitatively, the present results on neon clusters are in line with our previous results on argon clusters. In particular, surface location of barium was observed. The central part of the present work concerns neon clusters carrying both one barium atom and one to ten methane molecules. Several types of spectroscopy were performed in the region of the resonance transition (6s2)1S→(6s6p)1P of barium (excitation spectrum of the total fluorescence, emission spectrum, action spectrum for forming (6s6p)3P), and experiments where the number of methane molecules per cluster, which was strictly controlled, was varied systematically. The corresponding results were interpreted on the ground of a model, which transposes both chemical thermodynamics of equilibria and reaction kinetics to CICR experiments. Such an approach has a strong relationship, although it is more simple, with the thermodynamical approach to reactions in micellar solutions. The present thermodynamical model helped us to determine the origin of the action spectrum for forming Ba(6s6p)3P in clusters carrying both one barium atom and an average of 2.5 methane molecules. This action spectrum was assigned to direct excitation of the Ba(CH4) and Ba(CH4)2 complexes. The present thermodynamical model was also applied to our former results on argon clusters. This allowed us to derive a consistent picture of the association reaction of barium with methane and of the quenching of electronic excitation of barium by methane in both environments.