Angle-Resolved Photoemission of Solvated Electrons in Sodium-Doped Clusters

Angle-resolved photoelectron spectroscopy of the unpaired electron in sodium-doped water, methanol, ammonia, and dimethyl ether clusters is presented. The experimental observations and the complementary calculations are consistent with surface electrons for the cluster size range studied. Evidence against internally solvated electrons is provided by the photoelectron angular distribution. The trends in the ionization energies seem mainly determined by the degree of hydrogen bonding in the solvent and the solvation of the ion core. The onset ionization energies of water and methanol clusters do not level off at small cluster sizes, but decrease slightly with increasing cluster size

Drowning and aquatic injuries dictionary

Background Drowning is a significant public health issue with more than 320,000 deaths globally every year. These numbers are greatly underestimated, however, due to factors such as inadequate data collection, inconsistent categorization and failure to report in certain regions and cultures. The objective of this study was to develop a standardised drowning dictionary using a consensus-based approach. Through creation of this resource, improved clarity amongst stakeholders will be achieved and, as a result, so will our understanding of the drowning issue. Methodology A list of terms and their definitions were created and sent to 16 drowning experts with a broad range of backgrounds across four continents and six languages. A review was conducted using a modified Delphi process over five rounds. A sixth round was done by an external panel evaluating the terms’ content validity. Results The drowning dictionary included more than 350 terms. Of these, less than 10% had been previously published in peer review literature. On average, the external expert validity endorsing the dictionary shows a Scale Content Validity index (S-CVI/Ave) of 0.91, exceeding the scientific recommended value. Ninety one percent of the items present an I-CVI (Level Content Validity Index) value considered acceptable (> 0.78). The endorsement was not a universal agreement (S-CVI/UA:0.44). Conclusion The drowning dictionary provides a common language, and the authors envisage that its use will facilitate collaboration and comparison across prevention sectors, education, research, policy and treatment. The dictionary will be open to readers for discussion and further review at www.idra.world

Spectroscopy and Quantum-Dynamics: From Vibrations to Reactions

The physical understanding of chemical reactivity builds on the connection between structural and dynamical molecular properties, such as the specific dynamical properties of functional groups which determine a molecule's chemical behavior. Studies of OH- and NH2 groups in different environments demonstrate how experiment and theory combine to draw a detailed picture of the molecular quantum-dynamics. The hydrogen motion in a series of model systems elucidates important aspects of the N/O/H chemistry, with implications for radical and atmospheric chemistry. In perfect analogy to the separation of electronic and nuclear motion in the Born-Oppenheimer approximation, characteristic motions of individual structural features are adiabatically separated from the overall system dynamics. This phenomenon of vibrational adiabaticity will play a central role in the understanding of the microscopic foundations of empirical structure–reactivity relationships

Femtosecond quantum structure, equilibration and time reversal for the CH-chromophore dynamics in CHD2F

We present a new numerical scheme to compute femtosecond quantum molecular dynamics involving several strongly coupled degrees of freedom. This method is based on a combination of contracted grid basis eigenstate calculations with time-dependent propagation under coherent infrared multiphoton excitation with transformation to the quasi-resonant basis. Using data from our previous high-resolution spectroscopic investigation of CHD2F, we present quantum wavepacket results for the CH-chromophore dynamics, including coherent time evolution of CH stretching excitation in terms of explicit probability densities for the corresponding normal coordinate, relaxation towards approximate, partial quasi-equilibrium on the 100 fs time scale and a discussion of symmetry under time reversal in the ps time range

Size effects in the infrared spectra of NH3 ice nanoparticles studied by a combined molecular dynamics and vibrational exciton approach

Infrared extinction spectra of ammonia ice nanoparticles with radii between 2 and 10nm show pronounced band shape variations depending on the conditions of particle formation by collisional cooling. We present experimental and theoretical evidence showing that the variations in the region of the ν2 (umbrella) fundamental are due to changes in the particle size. The effect is analyzed in terms of an explicit atomistic model of the particles’ structure and vibrational dynamics. An explicit potential function combined with a novel extension of the vibrational exciton approach allows us to simulate extinction spectra for particles containing up to 16 000 atoms. It is shown that the particles formed under the conditions of our experiments consist of a crystalline core surrounded by an amorphous shell with an approximately constant thickness of 1–2nm. For the ν2 fundamental, this shell gives rise to a broad band [full width at half maximum (FWHM) 72cm−1] blueshifted by about 19cm−1 relative to a narrow peak (FWHM of 19cm−1) which arises from the crystalline core.ISSN:0021-9606ISSN:1089-769

Modeling of optical binding of submicron aerosol particles in counterpropagating Bessel beams

ISSN:1094-1622ISSN:0556-2791ISSN:1050-294

Phase, shape, and architecture of SF6 and SF6∕CO2 aerosol particles: Infrared spectra and modeling of vibrational excitons

Information on the phase, shape, and architecture of pure SF6 and mixed SF6 /CO2 aerosol particles is extracted from experimental infrared spectra by comparison with predictions from quantum mechanical exciton calculations. The radius of the particles lies around 50 nm. The following extensions to our previous vibrational exciton model are included: (i) To account for the many degrees of freedom of degenerate vibrational bands of aerosol particles, we take a time-dependent approach to calculate infrared absorption spectra directly from the dipole autocorrelation function. (ii) In addition to the dipole-dipole interaction, dipole-induced dipole terms are included to account for the high polarizability of SF6 and CO2. We find SF6 aerosol particles with a cubiclike shape directly after their formation and a change in the shape toward elongated particles with increasing time. Our microscopic model reveals that the cubic-to-monoclinic phase transition at 96 K found in the bulk cannot be observed with infrared spectroscopy because the two phases show almost identical spectra. Infrared spectra of two-component SF6 /CO2 particles with core-shell structure show characteristic split absorption bands for the shell. By contrast, homogeneously mixed SF6 /CO2 particles lead to broad infrared bands for both the core and the shell. The molecular origin of these various spectral features is uncovered by the analysis of the vibrational eigenfunctions.ISSN:0021-9606ISSN:1089-769

Intramolecular vibrational redistribution and unimolecular reaction : concepts and new results on the femtosecond dynamics and statistics in CHBrClF

We present the conceptual background for intramolecular vibrational (rotational) redistribution (IVR) in polyatomic molecules and its analysis from high resolution spectra. We illustrate some of the basic concepts relating to the use of effective and real molecular hamiltonians for IVR with examples drawn from our previous spectroscopic investigations of the chiral molecule CHFClBr. The importance of the initial state for the dynamics is shown, demonstrating that simple intuitive concepts of survival probabilities for some arbitrary chromophore (“zero order bright”) state are insufficient for a quantitative understanding of IVR. An approximate (C3‐like) symmetry prevents relaxation towards quasi‐equilibrium in highly excited C1‐asymmetrical CHFClBr. The coherent infrared multiphoton excitation of CHFClBr at the CH‐stretching frequency leads to coherent vibrational states with a very wide energy distribution corresponding to short time oscillatory behaviour of the CH‐stretching motion with a period of 11–12 fs. On longer time scales between 50 and 500 fs substantial vibrational motion is found in the CH‐bending coordinates. For modest excitation energies both the initial vibrational angular momentum quantum number (l = 0) and a' symmetry of the wavepacket are well conserved for 1–2 ps. At higher excitations and longer times (2–4 ps) these approximate symmetries are lost. These results are briefly discussed in relation to a general classification of IVR mechanisms and in relation to reactive processes in CHFClBr