Wave-particle duality is an inherent peculiarity of the quantum world. The double-slit experiment has been frequently used for understanding different aspects of this fundamental concept. The occurrence of interference rests on the lack of which-way information and on the absence of decoherence mechanisms, which could scramble the wave fronts. Here, we report on the observation of two-center interference in the molecular-frame photoelectron momentum distribution upon ionization of the neon dimer by a strong laser field. Postselection of ions, which are measured in coincidence with electrons, allows choosing the symmetry of the residual ion, leading to observation of both, gerade and ungerade, types of interference.

A generalised liquid-phase photoelectron spectroscopy approach is reported, allowing accurate, absolute energy scale ionisation energies of liquid water and aqueous solutions, as well as liquid water's work function to be reported.

Helium shows fascinating quantum phenomena unseen in any other element. In its liquid phase, it is the only known superfluid. The smallest aggregates of helium, the dimer (He 2 ) and the trimer (He 3 ) are, in their predicted structure, unique natural quantum objects. While one might intuitively expect the structure of 4 He 3 to be an equilateral triangle, a manifold of predictions on its shape have yielded an ongoing dispute for more than 20 years. These predictions range from 4 He 3 being mainly linear to being mainly an equilateral triangle. Here we show experimental images of the wave functions of 4 He 3 and 3 He 4 He 2 obtained by Coulomb explosion imaging of mass-selected clusters. We propose that 4 He 3 is a structureless random cloud and that 3 He 4 He 2 exists as a quantum halo state.

During the last 15 years a novel decay mechanism of excited atoms has been discovered and investigated. This so called "Interatomic Coulombic Decay" (ICD) involves the chemical environment of the electronically excited atom: the excitation energy is transferred (in many cases over long distances) to a neighbor of the initially excited particle usually ionizing that neighbor. It turned out that ICD is a very common decay route in nature as it occurs across van-der-Waals and hydrogen bonds. The time evolution of ICD is predicted to be highly complex, as its efficiency strongly depends on the distance of the atoms involved and this distance typically changes during the decay. Here we present the first direct measurement of the temporal evolution of ICD using a novel experimental approach.In 1997 Cederbaum and coworkers realized that the presence of loosely bound atomic or molecular neighbors opens a new relaxation pathway to an electronically excited atom or molecule. In the decay mechanism they proposed -termed Intermolecular Coulombic Decay (ICD) -the excited particle relaxes efficiently by transferring its excitation energy to a neighboring atom or molecule [1]. As a consequence the atom or molecule receiving the energy emits an electron of low kinetic energy. The occurrence of ICD was proven in experiments in the mid 2000s by means of electron spectroscopy [2] and multi-coincidence techniques [3]. Since that time a wealth of experimental and theoretical studies have shown that ICD is a rather common decay path in nature, as it occurs almost everywhere in loosely bound matter. It has been proven to occur after a manifold of initial excitation schemes such as innervalence shell ionization, after Auger cascades [4,5], resonant excitation [6,7], shakeup ionization [8] and resonant Auger decay. ICD has also been observed in many systems as rare gas clusters [9], even on surfaces [10] and small water droplets [11,12]. The latter suggested that ICD might play a role in radiation damage of living tissue [13], as it creates low energy electrons, which are known to be genotoxic [14,15]. More recently that scenario was reversed as it was suggested to employ ICD in treatment of tagged malignant cells [16]. Apart from these potential applications the elementary process of ICD is under investigation, as the decay is predicted to have a highly complex temporal * Electronic address: jahnke@atom.uni-frankfurt.de behavior. The efficiency and thus the decay times of ICD depend strongly on the size of the system, i.e. the number of neighboring particles and the distance between them and the excited particle. However, even for most simple possible model systems consisting of only two atoms the temporal evolution of the decay is non-trivial and predicted theoretically to exhibit exciting physics [17]: as ICD happens on a timescale that is fast compared to relaxation via photon emission, but comparable to the typical times of nuclear motion in the system, the dynamics of the decay is complicated and so far only theoretically explored...