Unbound Atoms Research Articles

D- and s-orbital populations in the d block: unbound atoms in physical vacuum versus chemical elements in condensed matter. A Dronskowski-population analysis

Abstract The electron configurations of Ca, Zn and the nine transition elements M in between (and their heavier homologs) are reviewed on the basis of density functional theory and experimental facts. The d-s orbital energy and population patterns are systematically diverse. (i) The dominant valence electron configuration of most free neutral atoms M0 of groups g = 2–12 is 3d g−2 4s 2 (textbook rule), or 3d g−14s 1. (ii) Formal M q+ cations in chemical compounds have the dominant configuration 3d g−q 4s 0 (basic concept of transition metal chemistry). (iii) M0 atoms in metallic phases [M∞] of hcp, ccp(fcc) and bcc structures have intermediate populations near 3d g−1 4s 1 (lower d populations for Ca (ca. ½) and Zn (ca. 10)). Including the 4p valence orbitals, the dominant metallic configuration is 3d g−δ 4(sp) δ with δ ≈ 1.4 (±0.2) throughout (except for Zn). (iv) The 3d,4s population of atomic clusters M m varies for increasing m smoothly from single-atomic 3d g−24s 2 toward metallic 3d g−14s 1. – The textbook rule for the one-electron energies, i.e., ns < (n−1)d, holds ‘in a broader sense’ for the s block, but in general not for the d block, and never for the p block. It is more important to teach realistic atomic orbital (AO) populations such as the ones given above.

SpectrumSDT: A program for parallel calculation of coupled rotational-vibrational energies and lifetimes of bound states and scattering resonances in triatomic systems

We present SpectrumSDT – a program for calculations of energies and lifetimes of bound rotational-vibrational states below and scattering resonances above the dissociation threshold on a global potential energy surface of a triatomic system, which may include stable molecules, weekly-bound van-der-Waals complexes, and unbound atom + diatom scattering systems. Large-amplitude vibrational motion is treated explicitly using hyper-spherical coordinates. Three options for the rotational-vibrational interaction are supported: uncoupled (symmetric top rotor), partially coupled (to include interaction between several nearest states only) and full-coupled (vibrating asymmetric-top rotor). In addition to energies and lifetimes, SpectrumSDT is able to integrate ro-vibrational wave functions over the user-defined regions of potential energy surface, which helps to classify these states. In this release of the code, SpectrumSDT is limited to ABA-type molecules with wave functions that do not extend into the regions near Eckart singularities. Program summaryProgram title: SpectrumSDTCPC Library link to program files:https://doi.org/10.17632/9gftxjs4yk.1Developer's repository link:https://github.com/IgorGayday/SpectrumSDTLicensing provisions: GNU General Public License 3 (GPL)Programming language: FortranNature of problem: Calculations of energies and lifetimes of bound rotational-vibrational states below and scattering resonances above the dissociation threshold on a global potential energy surface of a triatomic system, which may include stable molecules, weekly-bound van-der-Waals complexes, and unbound atom + diatom scattering systems.Solution method: A Hamiltonian matrix is built in APH coordinates using an optimal 2D basis set, adjusted for a given problem. A complex absorbing potential (CAP) is added to define a boundary condition for calculation of scattering resonances above the dissociation threshold. The eigenstates of the Hamiltonain matrix are found using a state-of-the-art iterative eigensolver.Restrictions: The present version is restricted to ABA-molecules and wave functions that do not extend into linear and equilateral triangle configurations.Additional comments including restriction and unusual features: Probabilities and lifetimes of the wave functions can be calculated in user-defined regions on the PES, which allows to analyze their localization properties (i.e. automatic isotopomer assignment) and obtain channel-specific lifetimes for scattering resonances.

Vibronic coupling induced by fast Rabi oscillations for kinetic energy control in free atom

Vibronic coupling effects usually manifest themselves in molecules and crystals rather than in unbound atoms. We theoretically demonstrate the existence of vibronic states in a moving two-level atom exposed to a strong electromagnetic (EM) wave. In this case, the Rabi oscillations of the electron density give rise to periodic displacements of the atomic nucleus with the Rabi frequency. The periodic displacements mix the Stark split electron levels and lead to the establishment of a channel for energy transfer in the atomic system. Such a channel paves the way for fast control of the kinetic energy of a free atom with the use of the parameters of an EM wave. Thus, the system kinetic energy can be decreased or increased if the detuning between the laser pulse frequency and the optical transition is positive or negative, respectively. For actual values of the detuning, the pulse duration should be an order of magnitude longer than the lifetime of the excited atomic level in order to complete the energy transfer process.

Effect of annealing temperature on thermoelectric properties of bismuth telluride thick film deposited by DC magnetron sputtering

We report the thermoelectric properties of thick bismuth-telluride (Bi2Te3) films deposited on polyimide substrates by DC magnetron sputtering and annealed at various temperatures (150–350 °C). The influence of annealing temperature on the microstructure and electronic structure of thick Bi2Te3 films is discussed. In this work, the annealed film at 250 °C has the best thermoelectric property due to highest electrical conductivity and Seebeck coefficient. The main effect of annealing temperature was really helpful to improve crystalline structure and enhance carrier mobility, whereas the carrier concentration was reduced due to the volatile of tellurium atom during annealing. Chemical states of bound and unbound atoms (Bi, Bi3+, Te, and Te2‐) on the surface play an important role in electrical properties. The exceed temperature caused the micro-crack formation and affect carrier transport by the scattering. The power factor of Bi2Te3 deposited by DC magnetron sputtering and annealed at 250 °C is comparable to the power factors of thick Bi2Te3 film deposited by various deposition techniques. The output power of single-leg, thick, thermoelectric Bi2Te3 film annealed at 250 °C as a function temperature generated a power of 0.98 μW at a temperature difference of 50 °C.

Calculation of scalar nuclear spin-spin coupling in a noble-gas mixture

Indirect spin-spin interactions between nuclei bound in a molecule are well-known in nuclear magnetic resonance, but such interactions between unbound atoms are less well studied and are often assumed to be zero. We present the first precision calculation of this interaction between 129Xe and 3He nuclei in a gas. Relativistic, state-of-the-art electronic structure theory is used to compute the scalar coupling constant J(R) and the interatomic potential energy function, V(R), as functions of the Xe-He internuclear distance R. Using virial expansion we find the nuclear spin enhancement factor kappa = -0.0105 +/- 0.0015 in excellent agreement with recent experiments. This interaction is particularly important for precision measurements using nuclear spin co-magnetometers.

Calculation and Analysis of Fractal Descriptors for Protein Amino Acids in Various Conformational States

A series of 20 proteinogenic amino acids was studied. Four types of fractal descriptors for 2 conformational states are calculated: α-helix and 1-strand β-sheet. Based on the analysis of the results obtained, it is established that when the conformational state of the amino acids (α-helix→β-sheet) changes, significant changes in the fractal descriptor Dtot, in the calculation of which all the atoms of the molecule are used, are not observed. However, the more specific descriptors Dval, Dvdw and Dunb, which reflect the aggregate of valence-coupled, van der Waals contact and unbound atoms, respectively, are more sensitive to the conformational transition. The increase Dval, Dvdw and the decrease Dunb values were established for a series of 7 amino acids.

Interplay between exotic superfluidity and magnetism in a chain of four-component ultracold atoms

We investigate the spin-polarized chain of ultracold fermionic atoms with spin-3/2 described by the fermionic Hubbard model with SU(4) symmetric attractive interaction. The competition of bound pairs, trions, quartets and unbound atoms is studied analytically and by density matrix renormalization group simulations. We find several distinct states where bound particles coexist with the ferromagnetic state of unpaired fermions. In particular, an exotic inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-type superfluid of quartets in a magnetic background of uncorrelated atoms is found for weaker interactions. We show that the system can be driven from this quartet-FFLO state to a molecular state of localized quartets which is also reflected in the static structure factor. For strong enough coupling, spatial segregation between molecular crystals and ferromagnetic liquids emerges due to the large effective mass of the composite particles.

Harmonic and subharmonic association of universal dimers in a thermal gas

In a gas of ultracold atoms whose scattering length is controlled by a magnetic Feshbach resonance, atoms can be associated into universal dimers by an oscillating magnetic field. In addition to the harmonic resonance with frequency near that determined by the dimer binding energy, there is a subharmonic resonance with half that frequency. If the thermal gas contains dimers, they can be dissociated into unbound atoms by the oscillating magnetic field. We show that the transition rates for association and dissociation can be calculated by treating the oscillating magnetic field as a sinusoidal time-dependent perturbation proportional to the contact operator. Many-body effects are taken into account through transition matrix elements of the contact operator. We calculate both the harmonic and subharmonic transition rates analytically for association in a thermal gas of atoms and dissociation in a thermal gas of dimers.

Defect Control and n-Doping of Encapsulated Graphene by Helium-Ion-Beam Irradiation.

We study with Raman spectroscopy the influences of He(+) bombardment and the environment on beam-induced defects in graphene encapsulated in hexagonal boron nitride (h-BN). We show for the first time experimentally the autonomous behavior of the D' defect Raman peak: in contrast to the D defect peak, the D' defect peak is sensitive to the local environment. In particular, it saturates with ion dose in the encapsulated graphene. Electrical measurements reveal n-type conduction in the BN-encapsulated graphene. We conclude that unbound atoms ("interfacials") between the sp(2)-layers of graphene and h-BN promote self-healing of the beam-induced lattice damage and that nitrogen-carbon exchange leads to n-doping of graphene.

Laser cooling of quasi-free atoms in a nondissipative optical lattice

A quasi-classical theory of laser cooling is applied to the analysis of cooling of unbound atoms with the angular momenta 1/2 in the ground and excited states in a one-dimensional nondissipative optical lattice. In the low-saturation limit with respect to the pumping field, the mechanisms of cooling can be interpreted within the framework of an effective two-level system of ground-state sublevels. In the limit of weak Raman transitions, the mechanism of cooling of unbound atoms is similar to the Doppler mechanism known in the theory of a two-level atom; in the limit of strong transitions, the mechanism of cooling is analogous to the well-known Sisyphys mechanism. In the slow-atom approximation, analytical expressions are obtained for the friction (drag) coefficient and the induced and spontaneous diffusion, and the kinetic temperature is estimated.

Polynomial algorithm of limited propositional deduction

For the problem of propositional satisfiability a polynomial algorithm of limited propositional deduction is proposed which can be viewed as a sort of boolean constraint propagation mechanism. It can be embodied in a backtracking search program for propositional satisfiability problems to make search efficient. The efficiency is gained in two ways: One is to use the algorithm to derive literals so as to overcome the ambiguities in search. The other is to exploit the consequence sets of unbound atoms generated during limited deduction as a heuristic measure for possible choices. The experiments have shown remarkable improvement in reducing search space.

Dissociation dynamics of fast neutral molecules scattered under glancing incidence conditions from crystal surfaces

When fast ( v thermal ⪡ v < v Fermi) neutral or ionised atoms or molecules are scattered under glancing incidence conditions from atomically smooth metal single crystal surfaces, translational energy losses of 0.1–1 eV per femtosecond or per Å of the trajectory in the near surface region are not atypical. A large fraction of this energy appears in the electron-hole pair excitation channel. In addition, the orientation distribution of the internuclear co-ordinate of dissociatively scattered molecules is often sharply peaked about the surface normal. Such a distribution could arise if, coincident with vibrational excitation of the intra-molecular co-ordinate, the molecules were preferentially aligned about the surface normal. Alternatively, such a distribution may arise if, following dissolution of the intra-molecular bond, the difference in the surface normal momentum transfer to the two unbound atoms considerably exceeds the difference in the surface parallel momentum transfer. We investigate these two possibilities within a classical simulation of energy transfer from the translational to internal degrees of freedom of the molecule via repeated transitions between different electronic states of the molecule-surface system. These simulations suggest that in general, the observed surface-normal aligned final orientation of dissociatively scattered molecules is caused by strong vibrational excitation in the entrance channel region of the adiabatic ground state potential energy surface describing the interaction of the neutral molecule with the surface.

The equilibrium pair distribution function of a gas: Aspects associated with the presence of bound states

At thermal equilibrium the momentum distribution of atoms in a gas is usually assumed to be Maxwellian, whether classically or quantally. However, if an atom is bound in a diatomic molecule, the atom’s momentum distribution is non-Maxwellian. This paper explores the consequent singlet and pair particle distribution functions in a gas having both unbound atoms and bound pairs of atoms. Comment is made on the range of behavior associated with whether the chemical equilibrium constant for diatom formation is small or large. Calculations of distribution functions and their moments for atoms which are members of dimers are presented for some specific model potentials.

Change of binding type and dissociation of molecules and biexcitons in a strong magnetic field

Hydrogen-like molecules (or biexcitons) in a strong magnetic field H > D 0 2μ B ( D 0 is the dissociation energy, μ B is the Bohr magneton) are considered. The electronic ground state corresponding to the total electron spin component S z = −1 along H in such a field is found to be either a state of the two unbound atoms or a molecule with S = 1, for sufficiently strong H; such a molecule shows a new type of binding, namely Van der Waals binding, induced by a magnetic field.

Conformation of O-methyl(phenyl) methylchlorophosphonates

1. From the IR spectra of the O-methyl(phenyl)methylchlorophosphonates it follows that the stabilization of one conformer is characteristic for these compounds. 2. Employing the method of dipole moments, it was determined that this confirmation can be either the form with a cis-position of the P=O and O-CH3 bonds, or with a gauche-position (the projection of OC is located between PO and PCl). 3. An estimate of the interactions of the unbound atoms disclosed that the latter conformation is more favorable.

Conformations of some phosphorous acid derivatives

1. The IR spectra of methyl dichlorophosphite were obtained in media of different polarity, in the temperature range 150–380°K. 2. The experimental dipole moment was determined. A comparison with the calculated values for the possible conformations led to selecting the cisoid form. 3. The practicality of this form for methyl dichlorophosphite, as well as for other phosphorous acid derivatives, was based on an analysis of the interactions of the unbound atoms.