We report on the effects of electron collision and indirect ionization processes, occurring at photoexcitation and electron kinetic energies well below 30 eV on the photoemission spectra of liquid water....

The fast evaporative cooling of micrometer-sized water droplets in a vacuum offers the appealing possibility to investigate supercooled water-below the melting point but still a liquid-at temperatures far beyond the state of the art. However, it is challenging to obtain a reliable value of the droplet temperature under such extreme experimental conditions. Here, the observation of morphology-dependent resonances in the Raman scattering from a train of perfectly uniform water droplets allows us to measure the variation in droplet size resulting from evaporative mass losses with an absolute precision of better than 0.2%. This finding proves crucial to an unambiguous determination of the droplet temperature. In particular, we find that a fraction of water droplets with an initial diameter of 6379±12  nm remain liquid down to 230.6±0.6  K. Our results question temperature estimates reported recently for larger supercooled water droplets and provide valuable information on the hydrogen-bond network in liquid water in the hard-to-access deeply supercooled regime.

Many soft-matter systems are composed of macromolecules or nanoparticles suspended in water. The characteristic times at intrinsic length scales of a few nanometres fall therefore in the microsecond and sub-microsecond time regimes. With the development of free-electron lasers (FELs) and fourth-generation synchrotron light-sources, time-resolved experiments in such time and length ranges will become routinely accessible in the near future. In the present work we report our findings on prototypical soft-matter systems, composed of charge-stabilized silica nanoparticles dispersed in water, with radii between 12 and 15 nm and volume fractions between 0.005 and 0.2. The sample dynamics were probed by means of X-ray photon correlation spectroscopy, employing the megahertz pulse repetition rate of the European XFEL and the Adaptive Gain Integrating Pixel Detector. We show that it is possible to correctly identify the dynamical properties that determine the diffusion constant, both for stationary samples and for systems driven by XFEL pulses. Remarkably, despite the high photon density the only observable induced effect is the heating of the scattering volume, meaning that all other X-ray induced effects do not influence the structure and the dynamics on the probed timescales. This work also illustrates the potential to control such induced heating and it can be predicted with thermodynamic models.

Liquid-jet photoelectron spectroscopy was applied to determine the first acid dissociation constant (p K a ) of aqueous-phase glucose while simultaneously identifying the spectroscopic signature of the respective deprotonation site. Valence spectra from solutions at pH values below and above the first p K a reveal a change in glucose’s lowest ionization energy upon the deprotonation of neutral glucose and the subsequent emergence of its anionic counterpart. Site-specific insights into the solution-pH-dependent molecular structure changes are also shown to be accessible via C 1s photoelectron spectroscopy. The spectra reveal a considerably lower C 1s binding energy of the carbon site associated with the deprotonated hydroxyl group. The occurrence of photoelectron spectral fingerprints of cyclic and linear glucose prior to and upon deprotonation are also discussed. The experimental data are interpreted with the aid of electronic structure calculations. Our findings highlight the potential of liquid-jet photoelectron spectroscopy to act as a site-selective probe of the molecular structures that underpin the acid–base chemistry of polyprotic systems with relevance to environmental chemistry and biochemistry.

Crystallization is a fundamental process in materials science, providing the primary route for the realization of a wide range of novel materials. Crystallization rates are considered also to be useful probes of glass-forming ability. [1][2][3]. At the microscopic level, crystallization is described by the classical crystal nucleation and growth theories [4, 5], yet in general solid formation is a far more complex process. Particularly the observation of apparently different crystal growth regimes in many binary liquid mixtures greatly challenges our understanding of crystallization [1, 6-12]. Here, we study by experiments, theory, and computer simulations the crystallization of supercooled mixtures of argon and krypton, showing that crystal growth rates in these systems can be reconciled with existing crystal growth models only by explicitly accounting for the non-ideality of the mixtures. Our results highlight the importance of thermodynamic aspects in describing the crystal growth kinetics, providing a major step towards a more sophisticated theory of crystal growth.The classical crystal nucleation and growth theories describe the microscopic steps by which a solid phase spontaneously forms in the supercooled liquid at some temperature T below melting.Homogeneous crystal nucleation is the process of the formation by thermal fluctuations of a small, localized nucleus of the newly ordered phase in the metastable liquid [4]. Once the nucleus has reached its critical size, it grows at a rate that within the kinetic theory of crystal growth is givenwhere f ≤ 1 is a geometrical factor representing the fraction of atomic collisions with the crystal surface that actually contribute to the growth, a(T ) is a characteristic interatomic spacing that can be identified with the lattice constant, ν(T ) is the crystal addition rate at the crystal/liquid interface, ∆S m is the molar entropy of fusion, R is the universal gas constant, and ∆G(T ) = G L (T ) − G C (T ) is the difference in liquid (L) and crystal (C) molar Gibbs free energies. In the Wilson-Frenkel (WF) theory [13], the crystal addition rate is proportional to the atomic diffusivity D(T ), ν WF (T ) = 6D(T )/Λ 2 (T ), and hence exhibits the strong temperature dependence associated with an activated process. Here, Λ(T ) = ca(T ) is an average atomic displacement that we assume to be proportional to a(T ), with c being a dimensionless parameter. In the collision-limited (CL) scenario [14], the crystal addition rate is proportional to the average thermal velocity of the particles, ν CL (T ) = 3k B T /m/Λ(T ), where k B is Boltzmann's constant and m is the particle's mass, and represents the extreme case in which there is no activation barrier for ordering.At the microscopic level, the WF and CL models can be characterized by limiting time scales

This corrects the article DOI: 10.1103/PhysRevLett.120.015501.

X-ray spectroscopy is a method, ideally suited for investigating the electronic structure of matter, which has been enabled by the rapid developments in light sources and instruments. The x-ray fluorescence lines of life-relevant elements such as carbon, nitrogen, and oxygen are located in the soft x-ray regime and call for suitable spectrometer devices. In this Letter, we present a high-resolution spectrum of liquid water, recorded with a soft x-ray spectrometer based on a reflection zone plate (RZP) design. The RZP-based spectrometer with meridional variation of line space density from 2953 to 3757 l/mm offers extremely high detection efficiency and, at the same time, medium energy resolution. We can reproduce the well-known splitting of liquid water in the lone pair regime with 10 s acquisition time.

The investigation of non-equilibrium phase transformations, such as crystallization, in supercooled liquids -below their melting point but still liquid -is of fundamental importance in condensed matter physics. However, accessing experimentally the details of such fast structural changes proves challenging.Here, we show that microscopic laminar jets in vacuum offer a powerful tool for novel studies of supercooled liquids on previously inaccessible time scales in a class of atomic and molecular model systems that have so far remained inaccessible because of the lack of adequate experimental approaches. The use of liquid jets represents a remarkable opportunity to significantly advance our knowledge of topics that are relevant to interdisciplinary fields such as atmospheric physics and material science. PACS 47.15.Uv % Laminar jets; 64.70.pm % Liquids; 64.60. My % Metastable phases; 64.70.dg % crystallization of specific substances; 61.05.cf % X-ray scattering (including small-angle scattering); 33.20.Fb % Raman and Rayleigh spectra (including optical scattering) ARTICLE HISTORY