We study the role of propagation of strong x-ray free-electron laser pulses on the Auger effect. When the system is exposed to a strong x-ray pulse the stimulated emission starts to compete with the Auger decay. As an illustration we present numerical results for Ar gas with the frequency of the incident x-ray pulse tuned in the 2p 3/2 -4s resonance. It is shown that the pulse propagation is accompanied by two channels of amplified spontaneous emission, 4s-2p 3/2 and 3s-2p 3/2 , which reshape the pulse when the system is inverted. The population inversion is quenched for longer propagation distances where lasing without inversion enhances the Stokes component. The results of simulations show that the propagation of the strong x-ray pulses affect intensively the Auger branching ratio.

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Resonant inelastic x-ray scattering spectra excited at the O1s −1 π * resonance of liquid acetone are presented. Scattering to the electronic ground state shows a resolved vibrational progression where the dominant contribution is due to the C-O stretching mode, thus demonstrating a unique sensitivity of the method to the local potential energy surface in complex molecular systems. For scattering to electronically excited states, soft vibrational modes and, to a smaller extent, intermolecular interactions give a broadening, which blurs the vibrational fine structure. It is predicted that environmental broadening is dominant in aqueous acetone.

Electron-density distributions and potential-energy surfaces are important for predicting the physical properties and chemical reactivity of molecular systems. Whereas angle-resolved photoelectron spectroscopy enables the reconstruction of molecular-orbital densities of condensed species 1 , absorption or traditional photoelectron spectroscopy are widely employed to study molecular potentials of isolated species. However, the information they provide is often limited because not all vibrational substates are excited near the vertical electronic transitions from the ground state. Moreover, many electronic states cannot be observed owing to selection rules or low transition probabilities. In many other cases, the extraction of the potentials is impossible owing to the high densities of overlapping electronic states. Here we use resonant photoemission spectroscopy, where the absence of strict dipole selection rules in Auger decay enables access to a larger number of final states as compared with radiative decay. Furthermore, by populating highly excited vibrational substates in the intermediate coreexcited state, it is possible to 'pull out' molecular states that were hidden by overlapping spectral regions before. Rydberg-Klein-Rees 2 is one of the most popular methods to reconstruct molecular potentials for stable states of diatomic molecules from rovibrational spectroscopy data without requiring any assumption about the shape of the potential. It is in a way a complementary method to the direct imaging of molecular orbitals to study molecular structures 3. Alternative approaches have been proposed on the basis of a fitting procedure of analytical potential functions to experimental data 2,4. Here we show how powerful the use of core excitation can be for extracting molecular-potential curves of ionic states exclusively on the basis of ultrahigh-resolution resonant photoemission (RPE) data as obtained for N 2. This has been achieved when controlling the extension of vibrational wavefunctions by fine tuning the X-ray energy. Indeed, tuning of the X-ray energy enables the spatial distribution of the vibrational wavefunctions in the intermediate state to be selected, and thus the extension of the probed region of the final-state potential to be controlled. Here we report the observation of the and 1 2 u states of N 2 + and the accurate reconstruction of the 1 2 g and molecular potentials, demonstrating that state-of-the-art RPE spectroscopy can be successfully used to solve the problem of potential reconstruction for excited molecular states directly from experimental data, and to identify such new states, invisible in conventional photoemission spectroscopy. Unlike direct photoemission, where the absorption of an X-ray photon of energyhω (where ω is the X-ray frequency) leads to the emission of a photoelectron, in the RPE process the resonant absorption of an X-ray photon populates final ionic states of the

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In this work, crystals FeSe x have been grown by flux approach. The crystallization process is divided into two stages. First, stoichiometric polycrystal FeSe 0.82 were sintered in a solid state reaction. Then, FeSe x crystals with a size about 500μm have been successfully grown in evacuated sealed quartz tube using a NaCl/KCl flux. The products include two crystal structures of tetragon and hexagon. The electronic transport and magnetic properties measurements of FeSe x crystal exhibit a superconducting transition at about 10K.

Resonant inelastic soft X-ray scattering (RIXS) spectra excited at the 1σg → 3σu resonance in gasphase O2 show excitations due to the nuclear degrees of freedom with up to 35 well resolved discrete vibronic states and a continuum due to the kinetic energy distribution of the separated atoms. The RIXS profile demonstrates spatial quantum beats caused by two interfering wave packets with different momenta as the atoms separate. Thomson scattering strongly affects both the spectral profile and the scattering anisotropy.PACS numbers: 33.20. Rm, 33.80.Gj, 33.20.Fb, 32.80.Aa Interference is a direct manifestation of the wave nature of matter, most clearly demonstrated in Young's double slit experiment. When a genuine double-slit experiment is performed with free atoms[1] care must be taken to make an atomic beam with sufficient temporal as well as spatial coherence for interference fringes to be observed. In spectroscopic studies double-slit analogues are encountered e. g. in the oscillatory time dependence of the decay probability following sudden excitation of two levels of a quantum system, referred to as quantum beats [2]. Spatial quantum beats [3], although conceptually more directly related to the wave nature of matter, have been given much less attention. Here we report on spatial quantum beats in resonant inelastic soft Xray scattering (RIXS) spectra of the O 2 molecule, where two dissociating states form the analogue of the double slit. Initially, the molecule is in the zero-point vibrational level of the electronic ground state. This defines the spatial initial conditions, and as the excitation process is fast in comparison to the nuclear motion also the temporal initial conditions are set. Depending on which state is excited the atoms separate with different speed, and thus their phase difference varies with internuclear distance. The resulting interference fringes are monitored in radiative transitions, which project the wavepacket development in discrete as well as continuum vibrational excitations of the electronic ground state.It has long been realized that the decay of core ex- * yuping@theochem.kth.se cited states in molecules contains information about the femtosecond nuclear dynamics during the excitationemission process [4]. In the electronic decay channel this feature is currently widely applied, and resonant Auger spectra excited at the same resonance that we use in the present study, the 1σ g → 3σ u resonance in O 2 , have been analyzed in detail [5]. Nuclear dynamics has also been addressed in RIXS experiments (see e.g. Refs [6-9]), in which dipole selection rules imply a high sensitivity to the symmetry of the wavefunctions, and simplify the interpretation of the spectra. In most studies, however, the energy resolution and counting statistics in the RIXS spectra have been compromised due to experimental limitations, and have not been in parity with what is achievable in resonant Auger spectra. With the new generation of instrumentation this is changing dramatically, and as we have recently ...

interactions (e.g., hydrogen bonds, π-π interactions, van der Waals forces) in the 2D plane. [5] Compared with their inorganic counterparts (i.e., 2D atomic crystals, such as graphene, transition metal dichalcogenides, and black phosphorus), the building blocks (i.e., the organic molecules) are soluble, enabling low temperature solution process on plastics for flexible electronics. [6][7][8] More importantly, the organic molecules can be designed with tailored electronic, optical, and magnetic properties, providing an unlimited number of perfect structures for both academic investigations and technical applications. [9,10] 2DMCs can be produced by both the top-down (TD) and the bottom-up (BU) approaches. The TD approach thins bulk organic single crystals down to nanometer scale by mechanical exfoliation. [11] As for inorganic crystals such as highly oriented pyrolytic graphite (HOPG), strong covalent bonds appear within one plane and the interplane interactions are weak van der Waals (vdW) forces. Due to the strong anisotropic interactions, such crystals can be exfoliated layer by layer to produce 2D atomic crystals (e.g., graphene). [12] However, in contrast to layered inorganic crystals, the bondings in organic crystals are typically weakly anisotropic, thus layer-by-layer exfoliation is inherently challenging. As a result, successful cases by the TD approach are scarce and the BU approach is considered more practical. The BU approach takes advantage of the solution processability of organic molecules and produces 2DMCs by solution self-assembly. [13,14] In this strategy, the structure of the organic semiconductor is the critical factor, because the interactions in the solids determine the morphologies and dimensions of the crystals. For example, Jiang and co-workers reported millimeter-sized 2DMCs by simple drop-casting, [15] a method widely used for bulk polycrystalline thin film preparation. Although the exact reason was not clear, the success for the growth of the molecularly thin 2DMC was ascribed to the structure of the semiconductor used, i.e., 1,4-bis((5ʹ-hexyl-2,2ʹ-bithiophen-5-yl)ethynyl)benzene (HTEB). [15] However, up to now, a precise molecular design towards 2DMCs is missing and little is known about the relationship between 2D self-assembly and molecular structure, hindering the practical application of the BU approach. [13] 2D molecular crystals (2DMCs) have attracted considerable attention because of their unique optoelectronic properties and potential applications. Taking advantage of the solution processability of organic semiconductors, solution self-assembly is considered an effective way to grow large-area 2DMCs. However, this route is largely blocked because a precise molecular design towards 2DMCs is missing and little is known about the relationship between 2D solution self-assembly and molecular structure. A "phase separation" molecular design strategy towards 2DMCs is proposed and layer-by-layer growth of millimeter-sized monolayer or few-layer 2DMCs is realized. High-performance orga...