References

Tetra-amino lithium and sodium complexes M(NH3)40,− (M=Li, Na) have one or two electrons that occupy diffuse orbitals distributed chiefly outside the M(NH3)4+ core. The lowest- energy 1s, 1p, and 1d orbitals follow Aufbau principles found earlier for beryllium tetra- ammonia complexes. Two ground state M(NH3)4 complexes can bind covalently by coupling their 1s1 electrons into a σ-type molecular orbital. The lowest excited states of the [M(NH3)4]2 species are obtained by promoting one or two electrons from this σ to other bonding or anti- bonding σ and π-type molecular orbitals. The electronic structure of solvated electron precursors provides insights into chemical bonding between super-atomic species that are present in concentrated alkali-metal-ammonia solutions.

This review summarizes experimental works performed over the last decade by several groups on the manipulation of a few individual interacting Rydberg atoms. These studies establish arrays of single Rydberg atoms as a promising platform for quantum-state engineering, with potential applications to quantum metrology, quantum simulation and quantum information.

Recent measurements of the reaction 2H(d,p)3H in metallic environments at very low energies performed by different experimental groups point to an enhanced electron screening effect. However, the resulting screening energies differ strongly for divers host metals and different experiments. Here, we present new experimental results and investigations of interfering processes in the irradiated targets. These measurements inside metals set special challenges and pitfalls which make them and the data analysis particularly error-prone. There are multi-parameter collateral effects which are crucial for the correct interpretation of the observed experimental yields. They mainly originate from target surface contaminations due to residual gases in the vacuum as well as from inhomogeneities and instabilities in the deuteron density distribution in the targets. In order to address these problems an improved differential analysis method beyond the standard procedures has been implemented. Profound scrutiny of the other experiments demonstrates that the observed unusual changes in the reaction yields are mainly due to deuteron density dynamics simulating the alleged screening energy values. The experimental results are compared with different theoretical models of the electron screening in metals. The Debye-Hiickel model that has been previously proposed to explain the influence of the electron screening on both nuclear reactions and radioactive decays could be clearly excluded.

Alkali metal compounds have been known since antiquity. In 1807, Sir Humphry Davy surprised everyone by electrolytically preparing (and naming) potassium and sodium metals. In 1808, he noted their interaction with ammonia, which, 100 years later, was attributed to solvated electrons. After 1960, pulse radiolysis of nearly any solvent produced solvated electrons, which became one of the most studied species in chemistry. In 1968, alkali metal solutions in amines and ethers were shown to contain alkali metal anions in addition to solvated electrons. The advent of crown ethers and cryptands as complexants for alkali cations greatly enhanced alkali metal solubilities. This permitted us to prepare a crystalline salt of Na− in 1974, followed by 30 other alkalides with Na−, K−, Rb− and Cs− anions. This firmly established the −1 oxidation state of alkali metals. The synthesis of alkalides led to the crystallization of electrides, with trapped electrons as the anions. Electrides have a variety of electronic and magnetic properties, depending on the geometries and connectivities of the trapping sites. In 2009, the final surprise was the experimental demonstration that alkali metals under high pressure lose their metallic character as the electrons are localized in voids between the alkali cations to become high-pressure electrides!

Abstract: In this study we report on the analysis of isothermal spectra of NH3 and ND3 solutions in liquid xenon at 203 K using newly developed and validated least-squares approaches to investigate the its self-associating behavior. For both species we observe clear dimer bands in the spectral area of the ν1+ν4, ν3+ν4 and ν1+ν2, ν3+ν2 combination bands. The analysis of the N−D stretching area, allows us to characterize clear contributions of dimers and trimers. The analysis of the N-H stretching area is hampered by the occurrence of a time dependent band due to solid water traces during the experiments. For NH3 we also performed an investigation of the N-H bending region, ν2, which demonstrated a small dimer absorption band. These obtained results compare well with literature data.

Abstract: We performed a series of plate impact experiments on NH3 gas initially at room temperature and at a pressure of ∼100 psi. Shocked states were determined by optical velocimetry and the temperatures by optical pyrometry, yielding compression ratios of ∼5–10 and second shock temperatures in excess of 7500 K. A first-principles statistical mechanical (thermochemical) approach that included chemical dissociation yielded reasonable agreement with experimental results on the principal Hugoniot, even with interparticle interactions neglected. Theoretical analysis of reshocked states, which predicts a significant degree of chemical dissociation, showed reasonable agreement with experimental data for higher temperature shots; however, reshock calculations required the use of interaction potentials. We rationalize the very different shock temperatures obtained, relative to previous results for argon, in terms of atomic versus molecular heat capacities.

The classical-trajectory Monte Carlo method has been used to investigate collisions of ions and Rydberg atoms in strong dc electric fields. Cross sections are presented for n = 10 and n = 20 Rydberg atoms at velocities 1 ^ v /ve ^1 0 where ve = n” 1 a.u. Electric fields which ionize product Rydberg atoms in states n’ – n + An with An = 1, 2, and 4 were used. The electric field caused the cross sections for electron capture to decrease by up to fourfold while the ionization values increased by up to two orders of magnitude.

Abstract: Classical-trajectory Monte Carlo calculations have been performed for collisions of ions in charge states q=+1, +2, +5 and +10 with hydrogenic atoms in principal quantum levels n=1, 2, 5, 10 and 20. The collision velocity range investigated was 1or=2. For v/ve>or approximately=5, the sum of the charge-exchange (CEX) and impact ionization (ION) cross sections may be represented by sigma CEX+ION(a02)=6 pi n2q2/v2, where v is in atomic units. Analysis of the electronic levels produced after charge exchange by the ion indicates the capture proceeds into excited levels which tend to preserve the energy and orbital size of the initial Rydberg atom.

Nuclear fusion reactions of D-D are examined in an environment comprised of high density cold fuel embedded in metal lattices in which a small fuel portion is activated by hot neutrons. Such an environment provides for enhanced screening of the Coulomb barrier due to conduction and shell electrons of the metal lattice, or by plasma induced by ionizing radiation (γ quanta). We show that neutrons are far more efficient than energetic charged particles, such as light particles (e−, e+) or heavy particles (p, d, α) in transferring kinetic energy to fuel nuclei (D) to initiate fusion processes. It is well known that screening increases the probability of tunneling through the Coulomb barrier. Electron screening also significantly increases the probability of large vs small angle Coulomb scattering of the reacting nuclei to enable subsequent nuclear reactions via tunneling. This probability is incorporated into the astrophysical factor S(E ). Aspects of screening effects to enable calculation of nuclear reaction rates are also evaluated, including Coulomb scattering and localized heating of the cold fuel, primary D-D reactions, and subsequent reactions with both the fuel and the lattice nuclei. The effect of screening for enhancement of the total nuclear reaction rate is a function of multiple parameters including fuel temperature and the relative scattering probability between the fuel and lattice metal nuclei. Screening also significantly increases the probability of interaction between hot fuel and lattice nuclei increasing the likelilhood of Oppenheimer-Phillips processes opening a potential route to reaction multiplication. We demonstrate that the screened Coulomb potential of the target ion is determined by the nonlinear Vlasov potential and not by the Debye potential. In general, the effect of screening becomes important at low kinetic energy of the projectile. We examine the range of applicability of both the analytical and asymptotic expressions for the well-known electron screening lattice potential energy Ue, which is valid only for E � Ue (E is the energy in the center of mass reference frame). We demonstrate that for E � Ue, a direct calculation of Gamow factor for screened Coulomb potential is required to avoid unreasonably high values of the enhancement factor f (E ) by the analytical—and more so by the asymptotic—formulas.

The structural and energetic proprieties for the Li + Xen (n = 1–18) clusters are investigated using both Basin- Hopping combined with Potential Model description (BH-PM) and DFT methods. A structural transition from tetrahedral (4 coordination) form to octahedral (6 coordination) one is observed for n = 6. Above this size, all structures have an octahedral core. The cubic-face-centered arrangement for xenon atoms is detected for Li + Xe14. To the best of our knowledge, the Li + Xen (n = 1–18) clusters are studied in the present work for the first time using the DFT theoretical approach. The M062X functional combined with aug-cc-pVDZ (for Li) and def2- TZVP (for Xe) basis sets reproduces accurately the CCSD(T) potential energy curve of Li + Xe system. Atom- Centered Density Matrix Propagation (ADMP) molecular dynamic calculations have been carried. Moreover, we investigate the larger sizes n = 31–35, 44, and 55 for the first time using the BH-PM theoretical approach. The closing of the first and second octahedron shells are proved for the n = 6 and 34 sizes, respectively. The relative stabilities of the Li + Xen molecules are also studied by computing the total energy, the binding energy per atoms for each size n. Then, the second energy difference between the size n and its two near neighbors allows iden- tifying the magic number series. Our present data are analyzed, discussed and compared with the available theoretical and experimental data.