Liquid drop and optical model calculations of elastic,vibrationally inelastic and absorptive scattering of4He atoms from4He n -clusters

The scattering of He atoms from liquid He _n -clusters withn=10 to 1000 at energies between 0.01 and 5.0 meV has been investigated by calculating integral cross sections for elastic scattering, absorption scattering and vibrational excitation of the liquid drop vibrations using a hard core potential, a transparent core potential, a black core and an optical model potential. The implications for planned scattering experiments are discussed.     

Erratum

A semi-empirical method for infrared, Raman and neutron inelastic scattering AH stretching band shape analysis in strong hydrogen bonded systems is proposed. The fast (n) and the slow (N) stretching modes are supposed to be adiabatically separable. In the fundamental state of the fast mode the adiabatic potential function for the slow mode is assumed to be harmonic and wavefunctions are known exactly. Profiles are assumed to be dominated by the short-time effects on the time dependent formulation for spectral intensities which are then determined by the overlap between the adiabatic wavefunction in the fundamental state and an Airy function depending on the slope of the upper potential function at the classical turning point, multiplied by the transition moment. Infrared, Raman and neutron inelastic scattering transition probabilities are derived including high order terms of the n,N electrical coupling. This method does not contradict earlier theories but it is believed to provide a more realistic band profile determination. Examples of computed spectra at low temperature are given which show that short-time effects and electrical coupling may account for typical band shapes of strong hydrogen bonded systems (ABC bands for instance) without supposing Fermi resonances. Evans-type interactions or a double minimum potential function for the proton motions.     

On the extraction of optical sums from experimental generalized oscillator strengths and the experimental determination of the x-ray incoherent scattering factory by electron scattering

The connection between an experimentally measured Bethe surface and certain optical sum rules is discussed. The simplest procedure for constructing optical sums involves summing (integrating) the generalized oscillator strength over energy loss at a fixed scattering angle. This involves an approximation and an error formula is developed to estimate the magnitude of the correction involved. The approximation is shown to be extremely accurate in the limit of high incident energy and large momentum transfer. The sum S(?1,K) which is simply related to the X-ray incoherent scattering factor is found to have a small first order correction in the case of electron scattering from He with 25 keV electrons even at angles as small as 1°.     

Electron scattering with H2S and PH3 molecules

Calculated total, differential and momentum transfer cross sections are reported for the vibrationally elastic scattering of electrons from H₂S and PH₃ molecules in the range of energy 0.1–50 eV. The scattering process is approximated by two incoherent scatterings caused, separately, by a central field and a long-range electric dipole interaction. The central field is calculated with a spherical approximate molecular wave function, in which the exchange interaction is treated in two ways: (i) exactly within the accuracy of the molecular wave function; (ii) approximately by a local model potential. The scattering by the central field is calculated with partial wave expansion technique, while the scattering by the electric dipole potential is calculated by using the first Born approximation for a rotating dipole model with experimental values of the dipole moments of H₂S and PH₃. The total cross sections are approximated by the incoherent sum of the cross section due to the central potential and the cross section of 00→10 rotational transition caused by the electric dipole potential. The effects of the polarization interaction are also tested. The contribution of small-angle scattering to the integral cross section is analyzed for these weakly polar molecules with some quantitative comparison.     

Spin polarization and cross sections of electrons elastically scattered from heavy alkaline-earth atoms

Semi-relativistic approach is employed to compute the differential and integrated cross sections, spin polarizationP and the spin polarization parametersT andU for the scattering of electrons from barium and strontium atoms in the energy range from 2.0–300 eV. The projectile-target interaction is represented both by real and complex optical potential in the solution of Dirac equation for the scattered electrons. The real optical potential includes the static, a parameter free correlation polarization and a modified semi classical exchange potentials. The complex optical potential is constructed by adding a model absorption potential as its imaginary part to the real optical potential.     

Electron and positron elastic scattering in gaseous and liquid water: A comparative study

In the present work, we present both theoretical differential and total cross sections for the elastic scattering process of positrons and electrons in liquid and vapour water for energies ranging from 10 eV to 10 keV. The calculations are performed in the partial-wave formalism by means of a complex interaction potential taking into account static potential as well as fine effects like exchange and polarization contributions. The theoretical results obtained in this free-parameter quantum-mechanical treatment are compared to available experimental data and good agreement is generally observed. Moreover, quantitative differences are reported between the positron and electron scattering, in vapour as well as in liquid water.     

Multiple collisions in molecular beam scattering experiments

Due to the forward peaked differential cross section for elastic atom—atom scattering the effect of multiple collisions has to be considered in the analysis of crossed beam measurements of the total cross section and especially of the small angle differential cross section at large values of the beam attenuation. At angles θ ≈ θ₀, with θ₀ the quantum mechanical scaling angle of the elastic differential cross section, the correction for the latter case amounts to 20% at beam attenuations I/I₀ = exp(?1). Firstly, a careful analysis of the probabilities for single and multiple scattering is given, resulting in an expression for the measured beam signals which is correct for all values of the beam attenuation. The probability for multiple scattering is then calculated for an inverse power potential V(r) = ?C_sr^?s, with s = 4 through s = 7, which include both the case of ion—atom scattering (s = 4) and atom—atom scattering (s = 6). The results are given as effective differential cross sections σ_n(θ) for n-fold scattering. They are described by a single, simple analytical function with four free parameters that have been determined for n = 2, 3 and 4 by a least squares method. The σ_n(θ) are normalised to the total cross section Q.     

Monte Carlo liquid water simulation with four-body interactions included

A four-body interaction potential for water molecules is derived. The new terms are combined with previously developed two- and three-body potential terms and applied in a Metropolis—Monte Carlo simulation at 298 K for an (N, V, T) ensemble with 512 water molecules. Improvements, relative to the results using only two-body, or two- and three-body interactions, are reported for the correlation function g(OO), for the X-ray and neutron-beam scattering intensities, and for the enthalpy.     

Effects of target gas in collision-induced dissociation using a double quadrupole mass spectrometer and radiofrequency

Collision-induced dissociation (CID) of polyatomic ions sampled from an rf-powered glow discharge is examined by using three target gases including atomic (Ar and Xe) and molecular species (N2). Collisions with these targets in the first quadrupole of the double quadrupole system result in the loss of discharge species by dissociation, symmetric and asymmetric charge exchange, and scattering, each to varying degrees. These processes are seen to be a function of the relative mass, size... and ionization potentials of the target species, as well as the collision center-of-mass energies. In light of the comparisons, xenon appears to be the best collision target for both CID and charge exchange because of its relatively low ionization potential and high dissociation efficiency of polyatornic species. Evidence for both symmetric and asymmetric charge exchange is presented for Ar and Xe target gases.     

Alignment and orientation effects in resonant charge exchange from laser excited Na*(3p)

A collisional alignment and orientation study with planar symmetry is described, determining the complete density matrix for resonant charge transfer from laser excited atoms. Results are reported for the Na⁺+Na*(3p) system over the collision energy rangeE _c.m.=50?100 eV. We communicate the optimal alignment angle γ and linear polarisationP _l ⁺ of the charge cloud as well as its relative height ρ₀₀ and the angular momentumL _⊥ ⁺ transferred in the collision as a function of the scattering angle. For preparation of the sodium 3p orbital in the scattering plane (positive reflection symmetry) we observe that at small reduced scattering angles (<20 eV°) the preparation of apσ at large internuclear distances contributes most to the scattering intensity whereas at larger reduced scattering angles (>60 eV°) apπ⁺ preparation is more important. In contrast, preparation of thepπ^? orbital (perpendicular to the scattering plane) is large at small and vanishes at larger scattering angles. We conclude that orbital following cannot be assumed in this resonant charge transfer process. The angular momentum transfer is observed to be small, indicating only little coherence in the process, but shows nevertheless an interesting behaviour as a function of scattering angle.     

Direct determination of scattering time delays using the S-matrix version of the Kohn variation method

A direct method for determining time delays for scattering processes is developed using the S-matrix version of the Kohn variation method recently reported by Miller. In this paper we develop a procedure for simultaneously determining both the S matrix and its energy derivative. Since only a small number of additional terms are needed to generate the energy derivative of the S matrix, this yields a direct method for determining scattering time delays that should be more attractive than the traditional methods based on numerical differentiation of #S#-matrix elements calculated at many closely spaced energies.     

Electron-molecule scattering with polarization using the schwinger variational principle

Electron-molecule scattering is formulated in an L² basis, using the Schwinger variational principle and including polarization via an ab initio optical potential. The necessary integrals are obtained in closed form. Electron-helium S-and P-wave phase shifts are calculated, and applications to molecules are mentioned.     

Computed static potentials for AHn molecules: a scattering-orintated form

A symmetry-adapted angular momentum factorization is reported for the density functions of non-linear molecules of the AH_n type with Z_A > 1, and for the static potentials generated by their ground state electronic configurations at equilibrium geometry. Results from one-centre expanded (OCE) wavefunctions are compared with those given by multicentre expansions and the rates of convergence for the electronic and nuclear terms are examined. The usefulness of such a factorization for dealing with electron-molecule scattering is discussed and its suitability in yielding molecule—molecule interactions pointed out for cases where the electron gas model is used to compute such potential surfaces.     

TiO2 nanoparticles synthesized in an aprotic solvent and applied to prepare high-refractive-index TiO2-polyimide hybrid thin films

In this study, very small (2–5 nm) TiO₂ nanoparticles were synthesized in an aprotic solvent, N,N-dimethylacetamide, via hydrolysis and condensation of titanium alkoxide at room temperature. The synthesized TiO₂ sol showed 30 days of storage stability and could be used to prepare high-refractive-index TiO₂-polyimide hybrid thin films by an ex-situ method that involved a spin coating and multistep baking process. The field emission scanning electron microscope image showed a flat and uniform morphology of the hybrid thin film. TiO₂ domains were in the nanometer range, thus avoiding light scattering. The refractive index at 633 nm of the hybrid thin film reached 2.05, which suggested potential applications of the film to anti-reflective coatings and optical waveguides.     

Delta-electron emission in fast heavy ion — atom collisions: observations of new phenomena and breakdown of common scaling laws

Double differential cross sections for the emission of Delta-electrons have been measured in fast uranium-rare gas collisions. The well-known Binary Encounter peak reveals unexpected structures for certain observation angles and its intensity increases towards smaller angles, which is in contradiction to results and scaling laws obtained by experiments with light ion impact. The observed dependencies are fairly well described by recent calculations in the framework of IA and CTMC. From systematic experimental as well as theoretical studies we can derive that the potential of the partially stripped projectile ion gives rise to rainbow and glory scattering of the target electron in the field of the projectile. The rainbow scattering is observed in the laboratory frame as pronounced interference structures, whereas the glory scattering is responsible for the steep increase of the cross sections for binary-encounter electrons towards small laboratory ejection angles. The observed effects have a dramatic influence on the commonq ² scaling laws derived from experiments with light ions. Furthermore, since the binary-encounter electrons ejected at forward angles have approximately twice the projectile velocity, these new phenomena have an important influence on the electronic stopping power of heavy ions and therefore have to be taken into account for the investigation of radiation damage by these ions e.g. in biological matter.     

Dittrichia graveolens (L.) Greuter,a Rapidly Spreading Invasive Plant: Chemistry and Bioactivity

Dittrichia graveolens L. Greuter belonging to the Asteraceae family, is an aromatic herbaceous plant native to the Mediterranean region. This plant species has been extensively studied for its biological activities, including antioxidant, antitumor, antimicrobial, antifungal, anti-inflammatory, anticholinesterase, and antityrosinase, and for its peculiar metabolic profile. In particular, bioactivities are related to terpenes and flavonoids metabolites, such as borneol (40), tomentosin (189), inuviscolide (204). However, D. graveolens is also well known for causing health problems both in animals and humans. Moreover, the species is currently undergoing a dramatic northward expansion of its native range related to climate change, now including North Europe, California, and Australia. This review represents an updated overview of the 52 literature papers published in Scopus and PubMed dealing with expansion, chemistry (262 different compounds), pharmacological effects, and toxicology of D. graveolens up to October 2021. The review is intended to boost further studies to determine the molecular pathways involved in the observed activities, bioavailability, and clinical studies to explore new potential applications.     

A generalized log-derivative method for the treatment of asymmetric collinear reactions in hyperspherical coordinates

The log-derivative method is applied to the treatment of collinear reactions using hyperspherical coordinates. As a test example the asymmetric reaction F + H₂ → FH + H on the Muckerman V potential surface is chosen. Extensive investigations of the convergence properties of the new “L-matrix propagation” program are carried out and it is shown that this is an accurate and efficient code for solving the (hyper)-radial coupled equations. Much attention is paid to a proper and effective treatment of some strong nonadiabatic effects occurring in asymmetric reactions. The curve crossing approximation is applied and its adequacy is demonstrated by comparison of the scattering matrices with the results obtained in the natural reaction coordinates approach. Modified versions of the two standard programs, the RXN1D and the S-matrix propagation program, were exploited in the performed tests.     

Large sodium clusters in an electrostatic field

We study light scattering by sodium clusters generated in a metal cell [3] and subjected to an external electrostatic field. Scattered laser light intensities at right angle to the incoming laser beam and with polarization parallel I _V and perpendicular I _H to that of the laser show two maxima as a function of the electrostatic field (potential of electrode): the central maximum CM for the zero field (V = 0) and the side maximum SM for ca. -60 V (field strength 2400 V/m). This behavior can be understood on the basis of the Mie scattering theory by taking into account electrostatic charging of clusters due to the laser light ionization of the medium (Na₂ molecules). The presented model leads to the conclusion that the electrostatic field changes cluster size, mainly due to the influence on the supersaturation of the medium. Clusters are charged with charge proportional to the cluster radius, only at SM clusters are neutral (zero charge). For electrode potential higher than SM clusters are positively charged, for smaller potential (more negative than SM) clusters are negatively charged.     

Spectroscopy and bonding in ternary metal hydride complexes—Potential hydrogen storage media

Of the challenges that are still to be met to enable the widespread use of H₂ as a fuel for automotive applications, a safe, reliable and cheap method for its storage and transportation is paramount. This need has prompted a massive effort in the synthesis and characterisation of novel hydrides and a better understanding of existing materials. In this review the vibrational spectroscopy and the bonding of a wide range of ternary metal hydride complexes are discussed. The spectroscopic techniques used include transmission and photoacoustic infrared spectroscopy, Raman spectroscopy with excitation wavelengths ranging from 1064 to 515 nm, inelastic neutron scattering spectroscopy and nuclear resonant inelastic X-ray scattering spectroscopy. The systems studied are: the octahedral transition metal hydrides, other geometry's of transition metal hydrides, alkali metal, alkaline earth and aluminium compounds with the borohydride ion, the alkali metal and alkaline earth alanates and the alkali metal gallates. In all cases, while the central atom is the most important determinant of the properties, it has become increasingly clear that the counter-ion is much more than just a spectator; it often plays a key role in determining the stability of the material. As such, varying the counter-ion provides an important mechanism for optimising the desired properties and these are reflected in the spectra. In addition to its use in characterising materials, vibrational spectroscopy is used to investigate reactions and processes. The advantages of vibrational spectroscopy lie in its flexibility: it is not restricted to crystalline systems, amorphous or nanocrystalline materials are readily observable, it is amenable to in situ studies, it is democratic; infrared and Raman spectroscopy are not element specific and uniquely among probes they are able to follow a reaction across a change of state. Vibrational spectroscopy and ab initio calculations are a synergistic pairing. Comparison of computed and experimental spectra provides a stringent test of the calculation, while the calculation provides unambiguous assignments of the spectra. Generation of the inelastic neutron scattering spectrum provides the most reliable test since only the amplitude of motion of the atoms in each mode is required.