PHYSICAL REVIEW LETTERS 102, 023003 (14 january 2009):

Fragmentation and Ionization Dynamics of C₆₀ in Elliptically Polarized Femtosecond Laser Fields

I.V. Hertel, I. Shchatsinin, T. Laarmann, N. Zhavoronkov, H.-H. Ritze, and C. P. Schulz

Ionization and fragmentation of C₆₀ fullerenes is studied in elliptically polarized, intense fs laser fields at 797 nm and contrasted with Xe⁺, utilizing time-of-flight mass spectrometry. Very pronounced changes of parent and fragment ion yield as a function of ellipticity are observed. At lower intensities reduction of the ion yield for circular polarization establishes a coherent two-photon process connected with the key role of the LUMO +1 ‘‘doorway state’’ and multielectron dynamics. Comparison with the behavior at 399 nm corroborates this finding. At high intensities enhanced fragmentation is observed which is tentatively attributed to returning loops of electron trajectories by the combined action of the C₆₀⁺ field and the circular laser field.

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Nature 455, 89-91 (4 September 2008):

Interaction between liquid water and hydroxide revealed by core-hole de-excitation

Emad F. Aziz, Niklas Ottosson, Manfred Faubel, Ingolf V. Hertel & Bernd Winter

The hydroxide ion plays an important role in many chemical and biochemical processes in aqueous solution. But our molecular-level understanding of its unusual and fast transport in water, and of the solvation patterns that allow fast transport, is far from complete. One proposal seeks to explain the properties and behaviour of the hydroxide ion by essentially regarding it as a water molecule that is missing a proton, and by inferring transport mechanisms and hydration structures from those of the excess proton. A competing proposal invokes instead unique and interchanging hydroxide hydration complexes, particularly the hypercoordinated OH^-(H₂O)₄ species and tri-coordinated OH^-(H₂O)₃ that can form a transient hydrogen bond between the H atom of the OH^- and a neighbouring water molecule. Here we report measurements of core-level photoelectron emission and intermolecular Coulombic decay for an aqueous hydroxide solution, which show that the hydrated hydroxide ion is capable of transiently donating a hydrogen bond to surrounding water molecules. In agreement with recent experimental studies of hydroxide solutions, our finding thus supports the notion that the hydration structure of the hydroxide ion cannot be inferred from that of the hydrated excess proton.

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Physical Review Letters 100, 023401 (15 January 2008):

Quantum Interference Spectroscopy of Rubidium-Helium Exciplexes Formed on Helium Nanodroplets

M. Mudrich, F. Stienkemeier, G. Droppelmann, P. Claas, and C. P. Schulz

Femtosecond multiphoton pump-probe photoionization is applied to helium nanodroplets doped with rubidium (Rb). The yield of Rb⁺ ions features pronounced quantum interference (QI) fringes demonstrating the coherence of a superposition of electronic states on a time scale of tens of picoseconds. Furthermore, we observe QI in the yield of formed RbHe exciplex molecules. The quantum interferogram allows us to determine the vibrational structure of these unstable molecules. From a sliced Fourier analysis one cannot only extract the population dynamics of vibrational states but also follow their energetic evolution during the RbHe formation.

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