Neutral Beryllium Research Articles

VECSEL systems for quantum information processing with trapped beryllium ions

We demonstrate two systems based on vertical-external-cavity surface-emitting lasers (VECSELs) for producing ultraviolet laser light at wavelengths of 235 and 313 nm. The systems are suitable for quantum information processing with trapped beryllium ions. Each system consists of a compact, single-frequency, continuous-wave VECSEL producing high-power near-infrared light, tunable over tens of nanometers. One system generates 2.4 W at 940 nm, using a gain mirror based on GaInAs/GaAs quantum wells, which is converted to 54 mW of 235 nm light for photoionization of neutral beryllium atoms. The other system uses a gain mirror based on GaInNAs/GaAs quantum wells, enabling wavelength extension above 1200 nm with manageable strain in the GaAs lattice. This system generates 1.6 W at 1252 nm, which is converted to 41 mW of 313 nm light that is used to laser cool trapped 9Be+ ions and quantum state preparation and detection. The 313 nm system is also suitable for implementing high-fidelity quantum gates.

A Neutral Beryllium(I) Radical.

The reduction of a cyclic alkyl(amino)carbene (CAAC)‐stabilized organoberyllium chloride yields the first neutral beryllium radical, which was characterized by EPR, IR, and UV/Vis spectroscopy, X‐ray crystallography, and DFT calculations.

Ein neutrales Beryllium(I)‐Radikal

AbstractDurch die Reduktion eines cyclischen Alkyl(amino)carben (CAAC)‐stabilisierten Organoberylliumchlorids konnte das erste neutrale Berylliumradikal erhalten werden, welches durch EPR‐, IR‐ und UV/Vis‐Spektroskopie, Röntgenkristallographie und DFT‐Rechnungen charakterisiert wurde.

Hylleraas-Configuration Interaction (Hy-CI) Non-Relativistic Energies for the 3 , 4 , 5 , 6 , and 7 Excited States of the Beryllium Atom.

In a previous work Sims and Hagstrom [J Chem Phys 140,224312(2014)] reported Hylleraas-configuration interaction (Hy-CI) method variational calculations for the 1 S ground states of the beryllium isoelectronic sequence with an estimated accuracy of 10 to 20 nanohartrees (nHa). In this work the calculations have been extended to the five higher states of the neutral beryllium atom, 3 1 S, 4 1 S, 5 1 S, 6 1 S, and 7 1 S. The best non-relativistic energies obtained for these states are -14.4182 4034 6, -14.3700 8789 0, -14.3515 1167 6,-14.3424 0357 8, and -14.3372 6649 96 Ha, respectively. The 6 1 S result is superior to the known reference energy for that state, while for the 7 1 S state there is no other comparable calculation.

Bayesian atomic structure calculations for collisional problems

SynopsisThe calculations of collisional processes require an accurate description of the target. In general, the atomic structure is obtained through tedious iterations in which a variety of configurations and parameters are chosen to minimize the differences between the numerical and experimental values of the energies and the oscillator strengths. Using a Bayesian machine learning analysis through a Tree–structured Parzen Estimator, we can reproduce the experimental atomic structure with high accuracy. Results for neutral beryllium are presented.

Characterization of the Ground States of BeC2 and BeC2- via Photoelectron Velocity Map Imaging Spectroscopy.

Due to their potentially unique properties, beryllium carbide materials have been the subject of many theoretical studies. However, experimental validation has been lacking due to the difficulties of working with Be. Neutral beryllium dicarbide has been predicted to have a T-shaped equilibrium structure (C2v), while previous quantum chemistry calculations for the structure of the anion had not yielded consistent results. In this study, we report photoelectron velocity map imaging spectra for the BeC2- X 2A1 → BeC2 X 1A1 transition. These data provide vibrational frequencies and the electron affinity of BeC2. Ab initio electronic structure calculations, validated against the experimental data, show that both the anion and the neutral form have C2v equilibrium geometries with polar covalent bonding between Be and the C2 subunit. Computed vibrational frequencies and the electron affinity, obtained at the CCSD(T) level of theory, were found to be in good agreement with the measurements.

Quantum information-based analysis of electron-deficient bonds.

Recently, the correlation theory of the chemical bond was developed, which applies concepts of quantum information theory for the characterization of chemical bonds, based on the multiorbital correlations within the molecule. Here, for the first time, we extend the use of this mathematical toolbox for the description of electron-deficient bonds. We start by verifying the theory on the textbook example of a molecule with three-center two-electron bonds, namely, diborane(6). We then show that the correlation theory of the chemical bond is able to properly describe the bonding situation in more exotic molecules which have been synthesized and characterized only recently, in particular, the diborane molecule with four hydrogen atoms [diborane(4)] and a neutral zerovalent s-block beryllium complex, whose surprising stability was attributed to a strong three-center two-electron π bond stretching across the C-Be-C core. Our approach is of high importance especially in the light of a constant chase after novel compounds with extraordinary properties where the bonding is expected to be unusual.

Complexes between H2 and neutral oxyacid beryllium derivatives. The role of angular strain

ABSTRACTThe complexes between 14 different Be-salts of oxyacids from groups 13 to 16 with one and two molecules of H2 have been investigated by means of the MP2/aug-cc-pVTZ ab initio molecular orbital theory method, which was found to be reliable for the treatment of these weakly bound species. The main conclusion is that these Be-salts yield rather stable complexes with dihydrogen, with binding energies one order of magnitude larger than other typical H2 complexes reported in the literature. This strong binding is shown to be due to an enhancement of the electron-deficient nature of Be when attached to an oxyacid moiety, which depends more on the type of coordination of the central atom of the oxyacid moiety. The formation of these complexes is followed by a significant lengthening of the H2 internuclear distance and a concomitant red-shift of the H–H stretching frequency, which becomes a good indicator of the strength of the interaction. The charge shifting from the bonding region of the H2 molecule to the interboundary Be···H2 region is the physical phenomenon behind the stability of these complexes. Accordingly, the most important contributor to this stability is the inductive term, followed by the electrostatic interactions. The ability of Be to bind H2 is enhanced by the angular arrangement of the O–Be–O electron-acceptor group.

Complexes between neutral oxyacid beryllium salts and dihydrogen: a possible way for hydrogen storage?

Accurate ab initio calculations reveal that oxyacid beryllium salts yield rather stable complexes with dihydrogen. The binding energies range between -40 and -60 kJ mol-1 for 1 : 1 complexes, remarkably larger than others previously reported for neutral H2 complexes. The second H2 molecule in 1 : 2 complexes is again strongly bound (between -18 and -20 kJ mol-1). The incoming H2 molecules in 1 : n complexes (n = 3-6) are more weakly bound, confirming the preference of Be for tetracoordinated arrangements.

Activation of Dinitrogen as A Dipolarophile in 1,3-Dipolar Cycloadditions: A Theoretical Study Using Nitrile Imines as \u201cOctet\u201d 1,3-Dipoles

Theoretical calculations at the G4MP2 level of theory demonstrate that it is possible to activate dinitrogen to make it react in dipolar cycloadditions using neutral beryllium derivatives and other neutral metallic compounds. For the particular case of beryllium, the barrier decreases more than 40 kJ·mol–1 with respect to the non-catalysed reaction. The activation achieved is lower than using diazonium salts (models of protonated N2), but still in a range that can be experimentally attainable.

Energetics and reactivity of small beryllium deuterides

Enthalpies and free energies of reaction for small neutral and charged beryllium deuterides BeD, BeD2, and BeD3 that have been calculated are reported for a temperature range of 0 K to 1000 K. We discuss probable dissociation channels and possible ways of producing BeD by localizing the relevant transition states and by calculating corresponding rate constants. BeD and BeD+ are found to be the most stable ones among the considered compounds. BeD2 and {mathrm{BeD}}_2^{+} are more likely to decompose into Be0,+ + D2 than into BeD0,+ + D. The metastable BeD3 and {mathrm{BeD}}_3^{+} predominantly decompose into BeD0,+ + D2. In light of our results on the reaction energetics, we can interpret the pathways for production of BeD via BeD2 and BeD3 intermediates observed in molecular dynamics simulations.

Calculations for electron-impact excitation and ionization of beryllium

The B-spline R-matrix and the convergent close-coupling methods are used to study electron collisions with neutral beryllium over an energy range from threshold to 100 eV. Coupling to the target continuum significantly affects the results for transitions from the ground state, but to a lesser extent the strong transitions between excited states. Cross sections are presented for selected transitions between low-lying physical bound states of beryllium, as well as for elastic scattering, momentum transfer, and ionization. The present cross sections for transitions from the ground state from the two methods are in excellent agreement with each other, and also with other available results based on nonperturbative convergent pseudostate and time-dependent close-coupling models. The elastic cross section at low energies is dominated by a prominent shape resonance. The ionization from the and states strongly depends on the respective term. The current predictions represent an extensive set of electron scattering data for neutral beryllium, which should be sufficient for most modeling applications.

Correlation energy, correlated electron density, and exchange-correlation potential in some spherically confined atoms.

We report correlation energies, electron densities, and exchange-correlation potentials obtained from configuration interaction and density functional calculations on spherically confined He, Be, Be2+ , and Ne atoms. The variation of the correlation energy with the confinement radius Rc is relatively small for the He, Be2+ , and Ne systems. Curiously, the Lee-Yang-Parr (LYP) functional works well for weak confinements but fails completely for small Rc . However, in the neutral beryllium atom the CI correlation energy increases markedly with decreasing Rc . This effect is less pronounced at the density-functional theory level. The LYP functional performs very well for the unconfined Be atom, but fails badly for small Rc . The standard exchange-correlation potentials exhibit significant deviation from the "exact" potential obtained by inversion of Kohn-Sham equation. The LYP correlation potential behaves erratically at strong confinements. © 2016 Wiley Periodicals, Inc.

Beryllepin, C6H6Be, and “Beryllium‐Inserted Benzenes,” C6H6Ben, n = 2–6: A Density Functional Computational Investigation

ABSTRACTThe seven‐membered beryllium‐containing heterocycle beryllepin, C6H6Be, has been examined computationally at the B3LYP/6‐311++G** density functional level of theory. Beryllepin is best described as a planar singlet heterocyclic conjugated triene with marginal aromatic character containing a C–Be–C moiety forced to be nonlinear (∠C‐Be‐C = 146.25°) by the cyclic constraints of the seven‐membered ring. The molecule can be considered to be derived from a benzene‐like system in which a neutral beryllium atom has been inserted between two adjacent carbon atoms. The 11 other possible “beryllium‐inserted benzenes,” C6H6Ben, n = 2–6, have also been investigated. Only two of these heterocyclic systems, the eight‐membered 1,4‐diberyllocin and the nine‐membered 1,4,7‐triberyllonin, were found to be stable, singlet‐ground‐state systems, albeit with little aromatic character. Of the remaining nine beryllium‐inserted benzenes, with the exception of the 11‐membered ring containing five beryllium atoms and the 12‐membered ring containing six beryllium atoms, which were calculated to exist as a ground state pentet and septet, respectively, all were calculated to be ground state triplet systems.

Electron collisions with beryllium and its ions

An overview is provided of the convergent close-coupling calculations for electron- impact on neutral beryllium, as well as its various ionic stages. The calculations were performed from near threshold to high energies with initial states having principal quantum number n ≤ 4. Excitation to states with n ≤ 5 and total ionisation cross sections have been calculated with an estimated accuracy of below 10% at all energies considered.

Hylleraas-configuration-interaction nonrelativistic energies for the ¹S ground states of the beryllium isoelectronic sequence.

In a previous work, Sims and Hagstrom ["Hylleraas-configuration-interaction study of the 1 (1)S ground state of neutral beryllium," Phys. Rev. A 83, 032518 (2011)] reported Hylleraas-configuration-interaction (Hy-CI) method variational calculations for the (1)S ground state of neutral beryllium with an estimated accuracy of a tenth of a microhartree. In this work, the calculations have been extended to higher accuracy and, by simple scaling of the orbital exponents, to the entire Be 2 (1)S isoelectronic sequence. The best nonrelativistic energies for Be, B(+), and C(++) obtained are -14.6673 5649 269, -24.3488 8446 36, and -36.5348 5236 25 hartree, respectively. Except for Be, all computed nonrelativistic energies are superior to the known reference energies for these states.

Atomic data and collisional–radiative model for beryllium and its ions

In this work we present a collisional–radiative model constructed for all ionization stages of beryllium. Convergent close-coupling, K-matrix and Coulomb–Born-exchange methods were applied to calculate the necessary atomic data. For the neutral beryllium atom a comparison of all methods is given. Fractional ion abundances, radiative power losses and electron cooling rates were calculated as functions of electron temperature. The comparison with other available data shows a rather good agreement.

All-solid-state continuous-wave laser systems for ionization, cooling and quantum state manipulation of beryllium ions

We describe laser systems for photoionization, Doppler cooling, and quantum state manipulation of beryllium ions. For photoionization of neutral beryllium, we have developed a continuous-wave 235 nm source obtained by two stages of frequency doubling from a diode laser at 940 nm. The system delivers up to 400 mW at 470 nm and 28 mW at 235 nm. For control of the beryllium ion, three laser wavelengths at 313 nm are produced by sum-frequency generation and second-harmonic generation from four infrared fiber lasers. Up to 7.2 W at 626 nm and 1.9 W at 313 nm are obtained using two pump beams at 1051 and 1551 nm. Intensity drifts of around 0.5 % per hour have been measured over 8 h at a 313 nm power of 1 W. These systems have been used to load beryllium ions into a segmented ion trap.

Hylleraas-configuration-interaction study of the1Sground state of neutral beryllium

Hylleraas-configuration-interaction (Hy-CI) method variational calculations are reported for the ${}^{1}S$ ground state of neutral beryllium. The best nonrelativistic energy obtained was $\ensuremath{-}14.667 356 4$ hartree, which is estimated to be accurate to a tenth of a microhartree.

Stark Width Regularities within Beryllium Spectral Series

AbstractThe dependences of Stark width on the upper-level ionization potential within different series of the neutral beryllium spectral lines have been studied. The dependences previously observed for electron impact contribution to the Stark widths were also obtained for the proton impact contribution. The emphasis is on the fine structure influence on the studied Stark parameter dependences. The influence of temperature on the dependences of Stark width parameters has been demonstrated. The relations found can be used in both cases for prediction of new Stark broadening data, thus avoiding much more complicated procedures.