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Michal Tomza - One of the best experts on this subject based on the ideXlab platform.
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ab initio electronic structure and prospects for the formation of ultracold calcium Alkali Metal Atom molecular ions
New Journal of Physics, 2020Co-Authors: Wissem Zrafi, Hela Ladjimi, Halima Said, H Berriche, Michal TomzaAbstract:Experiments with cold ion-Atom mixtures have recently opened the way for the production and application of ultracold molecular ions. Here, in a comparative study, we theoretically investigate ground and several excited electronic states and prospects for the formation of molecular ions composed of a calcium ion and an Alkali-Metal Atom: CaAlk+ (Alk=Li, Na, K, Rb, Cs). We use a quantum chemistry approach based on non-empirical pseudopotential, operatorial core-valence correlation, large Gaussian basis sets, and full configuration interaction method for valence electrons. Adiabatic potential energy curves, spectroscopic constants, and transition and permanent electric dipole moments are determined and analyzed for the ground and excited electronic states. We examine the prospects for ion-neutral reactive processes and the production of molecular ions via spontaneous radiative association and laser-induced photoassociation. After that, spontaneous and stimulated blackbody radiation transition rates are calculated and used to obtain radiative lifetimes of vibrational states of the ground and first-excited electronic states. The present results pave the way for the formation and spectroscopy of calcium--Alkali-Metal-Atom molecular ions in modern experiments with cold ion-Atom mixtures.
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ab initio properties of the ground state polar and paramagnetic europium Alkali Metal Atom and europium Alkaline earth Metal Atom molecules
Physical Review A, 2014Co-Authors: Michal TomzaAbstract:The properties of the electronic ground state of the polar and paramagnetic europium--$S\text{-state-Atom}$ molecules have been investigated. Ab initio techniques have been applied to compute the potential energy curves for the europium--Alkali-Metal-Atom, $\mathrm{Eu}X(X=\mathrm{Li},\mathrm{Na},\mathrm{K},\mathrm{Rb},\mathrm{Cs})$, europium--Alkaline-earth-Metal-Atom, $\mathrm{Eu}Y(Y=\mathrm{Be},\mathrm{Mg},\mathrm{Ca},\mathrm{Sr},\mathrm{Ba})$, and europium-ytterbium, EuYb, molecules in the Born-Oppenheimer approximation for the high-spin electronic ground state. The spin restricted open-shell coupled cluster method restricted to single, double, and noniterative triple excitations, RCCSD(T), was employed and the scalar relativistic effects within the small-core energy-consistent pseudopotentials were included. The permanent electric dipole moments and static electric dipole polarizabilities were computed. The leading long-range coefficients describing the dispersion interaction between Atoms at large internuclear distances ${C}_{6}$ are also reported. The EuK, EuRb, and EuCs molecules are examples of species possessing both large electric and magnetic dipole moments making them potentially interesting candidates for ultracold many-body quantum simulations when confined in an optical lattice in combined electric and magnetic fields.
W Happer - One of the best experts on this subject based on the ideXlab platform.
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Alkali Metal Atom polarization imaging in high pressure optical pumping cells
Physical Review A, 1998Co-Authors: Benamar A Baranga, S Appelt, A R Young, C J Erickson, W HapperAbstract:We present a detailed experimental analysis of Rb-polarization imaging in high-pressure gas cells. The Rb vapor in these cells is optically pumped by high-power diode-laser arrays. We present images for high (35 G) and low (4 G) magnetic fields and for different He and Xe buffer-gas mixtures. We demonstrate that high-field imaging provides an absolute measurement of the Rb-polarization distribution in the cell, based on the fact that a spin-temperature distribution of the hyperfine magnetic sublevels is established in high-pressure buffer gases. A survey of various mechanisms that broaden the Rb magnetic-resonance lines is presented. These broadening mechanisms determine the limits of the spatial resolution achievable for images of the Rb-polarization distribution.
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theory of spin exchange optical pumping of 3 he and 129 xe
Physical Review A, 1998Co-Authors: S Appelt, Benamar A Baranga, A R Young, C J Erickson, M V Romalis, W HapperAbstract:We present a comprehensive theory of nuclear spin polarization of ${}^{3}\mathrm{He}$ and ${}^{129}\mathrm{Xe}$ gases by spin-exchange collisions with optically pumped Alkali-Metal vapors. The most important physical processes considered are (1) spin-conserving spin-exchange collisions between like or unlike Alkali-Metal Atoms; (2) spin-destroying collisions of the Alkali-Metal Atoms with each other and with buffer-gas Atoms; (3) electron-nuclear spin-exchange collisions between Alkali-Metal Atoms and ${}^{3}\mathrm{He}$ or ${}^{129}\mathrm{Xe}$ Atoms; (4) spin interactions in van der Waals molecules consisting of a Xe Atom bound to an Alkali-Metal Atom; (5) optical pumping by laser photons; (6) spatial diffusion. The static magnetic field is assumed to be small enough that the nuclear spin of the Alkali-Metal Atom is well coupled to the electron spin and the total spin is very nearly a good quantum number. Conditions appropriate for the production of large quantities of spin-polarized ${}^{3}\mathrm{He}$ or ${}^{129}\mathrm{Xe}$ gas are assumed, namely, atmospheres of gas pressure and nearly complete quenching of the optically excited Alkali-Metal Atoms by collisions with ${\mathrm{N}}_{2}$ or ${\mathrm{H}}_{2}$ gas. Some of the more important results of this work are as follows: (1) Most of the pumping and relaxation processes are sudden with respect to the nuclear polarization. Consequently, the steady-state population distribution of Alkali-Metal Atoms is well described by a spin temperature, whether the rate of spin-exchange collisions between Alkali-Metal Atoms is large or small compared to the optical pumping rate or the collisional spin-relaxation rates. (2) The population distributions that characterize the response to sudden changes in the intensity of the pumping light are not described by a spin temperature, except in the limit of very rapid spin exchange. (3) Expressions given for the radio-frequency (rf) resonance linewidths and areas can be used to make reliable estimates of the local spin polarization of the Alkali-Metal Atoms. (4) Diffusion effects for these high-pressure conditions are mainly limited to thin layers at the cell surface and at internal resonant surfaces generated by radio-frequency magnetic fields when the static magnetic field has substantial spatial inhomogeneities. The highly localized effects of diffusion at these surfaces are described with closed-form analytic functions instead of the spatial eigenmode expansions that are appropriate for lower-pressure cells.
Debra J. Searles - One of the best experts on this subject based on the ideXlab platform.
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Graphyne and graphdiyne: Versatile catalysts for dehydrogenation of light Metal complex hydrides
The Journal of Physical Chemistry C, 2013Co-Authors: Y. Song, Debra J. SearlesAbstract:The interaction between new two-dimensional carbon allotropes, i.e. graphyne (GP) and graphdiyne (GD), and light Metal complex hydrides LiAlH4, LiBH4, and NaAlH4 was studied using density functional theory (DFT) incorporating long range van der Waals dispersion correction. The light Metal complex hydrides show much stronger interaction with GP and GP than that with fullerene due to the well defined pore structure. Such strong interactions greatly affect the degree of charge donation from the Alkali Metal Atom to AlH4 or BH4, consequently destabilizing the Al-H or B-H bonds. Compared to the isolated light Metal complex hydride, the presence of GP or GD can lead to a significant reduction of the hydrogen removal energy. Most interestingly, the hydrogen removal energies for LiBHx on GP and with GD are found to be lowered at all the stages (x from 4 to 1) whereas the H-removal energy in the third stage is increased for LiBH4 on fullerene. In addition, the presence of uniformly distributed pores on GP and GD is expected to facilitate the dehydrogenation of light Metal complex hydrides. The present results highlight new interesting materials to catalyze light Metal complex hydrides for potential application as media for hydrogen storage. Since GD has been successfully synthesized in a recent experiment, we hope the present work will stimulate further experimental investigations in this direction.
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Graphyne and Graphdiyne: Versatile Catalysts for Dehydrogenation of Light Metal Complex Hydrides
2013Co-Authors: Y. Song, Debra J. SearlesAbstract:The interaction between new two-dimensional carbon allotropes, i.e., graphyne (GP) and graphdiyne (GD), and light Metal complex hydrides LiAlH4, LiBH4, and NaAlH4 was studied using density functional theory (DFT) incorporating long-range van der Waals dispersion correction. The interaction of light Metal complex hydrides with GP and GD is much stronger than that with fullerene because of the well-defined pore structure of GP and GD. Such strong interactions greatly affect the degree of charge donation from the Alkali Metal Atom to AlH4 or BH4, consequently destabilizing the Al–H or B–H bonds. Compared to the isolated light Metal complex hydride, the presence of GP or GD can lead to a significant reduction of the hydrogen removal energy. Most interestingly, the hydrogen removal energies for LiBHx on GP and with GD are found to be lowered at all the stages (x from 4 to 1), whereas the H-removal energy in the third stage is increased for LiBH4 on fullerene. In addition, the presence of uniformly distributed pores on GP and GD is expected to facilitate the dehydrogenation of light Metal complex hydrides. The present results highlight new interesting materials to catalyze light Metal complex hydrides for potential application as media for hydrogen storage. Because GD has been successfully synthesized in a recent experiment, we hope the present work will stimulate further experimental investigations in this direction
Uwe Thumm - One of the best experts on this subject based on the ideXlab platform.
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negative ion resonances in cross sections for slow electron heavy Alkali Metal Atom scattering
Physical Review A, 2001Co-Authors: Cristian Bahrim, Uwe Thumm, I I FabrikantAbstract:We analyze negative-ion resonances in elastic and inelastic total scattering cross sections for slow electron collisions with the heavy-Alkali-Metal Atoms Rb, Cs, and Fr. Our calculations are based on the Dirac $R$-matrix method [Thumm and Norcross, Phys. Rev. A 45, 6349 (1992)]. For incident electrons of up to 2.8 eV kinetic energy, we compare a ${}^{3}{P}^{o}$ shape resonance and ${}^{3}{P}^{e},$ ${}^{1}{P}_{1}^{o},$ and ${}^{1}{D}_{2}^{o}$ Feshbach resonances, located below the first excitation threshold of the Atomic target in the low-lying spectra of the ${\mathrm{Rb}}^{\ensuremath{-}},$ ${\mathrm{Cs}}^{\ensuremath{-}},$ and ${\mathrm{Fr}}^{\ensuremath{-}}$ negative ions, with available experimental data and other calculations. We provide the resonance parameters, partial and converged total elastic and inelastic scattering cross sections, and discuss the relative importance of relativistic effects for the three heavy-Alkali-Metal targets.
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relativistic r matrix calculations for electron Alkali Metal Atom scattering cs as a test case
Physical Review A, 1992Co-Authors: Uwe Thumm, D W NorcrossAbstract:We have reformulated the Dirac {ital R}-matrix method for low-energy electron scattering by (effectively) one-electron, Alkali-Metal-like systems and developed an independent computer program for this special purpose. A highly accurate and relativistic representation of the target was used to perform a multichannel close-coupling calculation of cross sections for electron scattering. Our results include the negative-ion affinity and elastic, inelastic, and total cross sections for incident electrons with 0 to 2.8 eV kinetic energy. We find that core-polarization and relativistic effects lead to multiplets of very narrow {sup 3}{ital P}{sub {ital J}}, {ital J}=0,1,2 shape resonances: the effect of the induced core polarization on the electron-electron correlation leads to 6{ital s}6{ital p}{sup 3}{ital P}{sub {ital J}}{sup {ital o}} resonances in contrast to previously predicted bound states of Cs{sup {minus}}, and relativistic interactions are responsible for the autoionizing decay of 6{ital p}{sup 2} {sup 3}{ital P}{sub {ital J}} states below the first excitation threshold.
Koichi Ohno - One of the best experts on this subject based on the ideXlab platform.
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photoionization efficiency curve measurements of Alkali Metal Atom methyl propiolate clusters observation of intracluster cyclotrimerization products
Journal of Physical Chemistry A, 2004Co-Authors: Hironori Tsunoyama, Fuminori Misaizu, Koichi OhnoAbstract:Reaction products in clusters containing an Alkali Metal Atom (M = Na, K, and Cs) and methyl propiolate (MP) molecules have been examined from results of photoionization efficiency (PIE) curve measurements. Two distinct humps were commonly observed in the PIE curves of Cs(MP) n for n ≥ 3, whereas a relatively smooth curve was obtained for n = 2. In the photoionization mass spectra of M(MP) n , an intensity anomaly at n = 3 was commonly observed as reported in the previous paper, which was due to a cyclotrimerization reaction producing a benzene derivative (trimethyl benzenetricarboxylate, BT). From the results of quantum chemical calculations for reacted and unreacted isomers, these two humps originate from two isomers with different ionization thresholds; the lower threshold is ascribed to a solvation-type isomer, Cs(MP) 3 , and the higher value comes from a reacted isomer composed of a cesium Atom and a BT molecule. From the relative intensity of two isomers, the intracluster cyclotrimerization reaction producing BT is found to proceed efficiently in the present M-MP clusters.
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photoionization mass spectroscopy of clusters of Alkali Metal Atoms with methyl vinyl ketone and acrolein intracluster oligomerization initiated by electron transfer from a Metal Atom
International Journal of Mass Spectrometry, 2002Co-Authors: Keijiro Ohshimo, Hironori Tsunoyama, Fuminori Misaizu, Ari Furuya, Koichi OhnoAbstract:Abstract We have investigated the photoionization mass spectrometry of clusters of an Alkali Metal Atom (M: Na and K) and methyl vinyl ketone (MVK) or acrolein (AC) to discuss the intracluster oligomerization. In the mass spectra of M(MVK) n , strong ion signals at n =3 are observed. This magic number is explained by the cyclohexane derivative formation in the intracluster oligomerization of MVK initiated by electron transfer from an Alkali Metal Atom. The results of the calculation for Na(MVK) based on density functional theory also show the presence of intracluster electron transfer. On the other hand, in M(AC) n , intensity enhancement is observed at n =4. These intensity enhancements may be due to intracluster reaction in M(AC) n , which is different from the case of M(MVK) n .
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intracluster anionic oligomerization of acrylic ester molecules initiated by electron transfer from an Alkali Metal Atom
Journal of the American Chemical Society, 2001Co-Authors: Hironori Tsunoyama, Fuminori Misaizu, Keijiro Ohshimo, Koichi OhnoAbstract:Stabilities and intracluster reactions have been investigated by photoionization mass spectrometry for clusters composed of an Alkali Metal Atom (M; Na and K) and acrylic ester molecules, CH2CHCO2R, such as methyl acrylate (MA; R = CH3) and ethyl acrylate (EA; R = C2H5). The following two features are commonly observed in the photoionization mass spectra of M(CH2CHCO2R)n: (1) The ion with n = 3 is clearly observed as a magic number. (2) Fragmented cluster ions with the loss of ROH, [M(CH2CHCO2R)n − ROH] are detected only for n = 3. These features are both explained by an intracluster oligomerization reaction initiated by electron transfer from the Metal Atoms. The magic number trimer is concluded to have the stable structure of cyclohexane derivatives as a result of oligomerization. The fragmentation reaction is explained by Dieckmann cyclization after anionic oligomerization to produce another isomer of the trimer. The intracluster electron transfer is also supported by theoretical calculation for Na(MA...
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photoionization and density functional theory study of clusters of acetone containing an Alkali Metal Atom m ch3 2co n m li na intracluster electron transfer from Metal to acetone in 1 1 complexes
Chemical Physics Letters, 2000Co-Authors: Hironori Tsunoyama, Fuminori Misaizu, Keijiro Ohshimo, Yoshihiro Yamakita, Koichi OhnoAbstract:Abstract Ionization threshold energies of clusters of Li and Na Atoms solvated by acetone have been determined by laser photoionization. The thresholds for 1:1 complexes agree well with calculated adiabatic ionization potentials based on density functional theory. The structures and charge distributions obtained from the calculation show that electron transfer from the Alkali Atom to acetone occurs more efficiently in Li((CH3)2CO) than in Na((CH3)2CO). This difference in the extent of electron transfer can be understood by a consideration of the orbital overlap between the Metal np and O2p orbitals and the sp hybridization on the Alkali Atom.