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Title: Absorption spectroscopy of heavy alkaline earth metals Ba and Sr in rare gas matrices—CCSD(T) calculations and atomic site occupancies

Abstract

Isolation of the heavier alkaline earth metals Ba and Sr in the solid rare gases (RGs) Ar, Kr, and Xe is analysed with absorption spectroscopy and interpreted partly with the assistance of ab initio calculations of the diatomic M ⋅ RG ground state interaction potentials. The y{sup 1}P←a{sup 1}S resonance transitions in the visible spectral region are used to compare the isolation conditions of these two metal atom systems and calcium. Complex absorption bands were recorded in all three metal atom systems even after extensive sample annealing. Coupled cluster calculations conducted on the ground states of the nine M ⋅ RG diatomics (M = Ca, Sr, and Ba; RG = Ar, Kr, and Xe) at the coupled cluster single, double, and non-iterative triple level of theory revealed long bond lengths (>5 Å) and shallow bound regions (<130 cm{sup −1}). All of the M ⋅ RG diatomics have bond lengths considerably longer than those of the rare gas dimers, with the consequence that isolation of these metal atoms in a single substitutional site of the solid rare gas is unlikely, with the possible exception of Ca/Xe. The luminescence of metal dimer bands has been recorded for Ba and Sr revealing verymore » different behaviours. Resonance fluorescence with a lifetime of 15 ns is observed for the lowest energy transition of Sr{sub 2} while this transition is quenched in Ba{sub 2}. This behaviour is consistent with the absence of vibrational structure on the dimer absorption band in Ba{sub 2} indicating lifetime broadening arising from efficient relaxation to low-lying molecular states. More extensive 2D excitation-emission data recorded for the complex site structures present on the absorption bands of the atomic Ba and Sr systems will be presented in future publications.« less

Authors:
;  [1]
  1. Department of Chemistry, Maynooth University, National University of Ireland—Maynooth, County Kildare (Ireland)
Publication Date:
OSTI Identifier:
22493694
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 144; Journal Issue: 4; Other Information: (c) 2016 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ABSORPTION SPECTROSCOPY; ARGON; ATOMS; BARIUM; BOND LENGTHS; CALCIUM COMPLEXES; DIMERS; EXCITATION; GROUND STATES; ITERATIVE METHODS; KRYPTON; LIFETIME; MATRIX MATERIALS; RELAXATION; RESONANCE FLUORESCENCE; SOLIDS; STRONTIUM; XENON

Citation Formats

Davis, Barry M., and McCaffrey, John G., E-mail: john.mccaffrey@nuim.ie. Absorption spectroscopy of heavy alkaline earth metals Ba and Sr in rare gas matrices—CCSD(T) calculations and atomic site occupancies. United States: N. p., 2016. Web. doi:10.1063/1.4940688.
Davis, Barry M., & McCaffrey, John G., E-mail: john.mccaffrey@nuim.ie. Absorption spectroscopy of heavy alkaline earth metals Ba and Sr in rare gas matrices—CCSD(T) calculations and atomic site occupancies. United States. doi:10.1063/1.4940688.
Davis, Barry M., and McCaffrey, John G., E-mail: john.mccaffrey@nuim.ie. Thu . "Absorption spectroscopy of heavy alkaline earth metals Ba and Sr in rare gas matrices—CCSD(T) calculations and atomic site occupancies". United States. doi:10.1063/1.4940688.
@article{osti_22493694,
title = {Absorption spectroscopy of heavy alkaline earth metals Ba and Sr in rare gas matrices—CCSD(T) calculations and atomic site occupancies},
author = {Davis, Barry M. and McCaffrey, John G., E-mail: john.mccaffrey@nuim.ie},
abstractNote = {Isolation of the heavier alkaline earth metals Ba and Sr in the solid rare gases (RGs) Ar, Kr, and Xe is analysed with absorption spectroscopy and interpreted partly with the assistance of ab initio calculations of the diatomic M ⋅ RG ground state interaction potentials. The y{sup 1}P←a{sup 1}S resonance transitions in the visible spectral region are used to compare the isolation conditions of these two metal atom systems and calcium. Complex absorption bands were recorded in all three metal atom systems even after extensive sample annealing. Coupled cluster calculations conducted on the ground states of the nine M ⋅ RG diatomics (M = Ca, Sr, and Ba; RG = Ar, Kr, and Xe) at the coupled cluster single, double, and non-iterative triple level of theory revealed long bond lengths (>5 Å) and shallow bound regions (<130 cm{sup −1}). All of the M ⋅ RG diatomics have bond lengths considerably longer than those of the rare gas dimers, with the consequence that isolation of these metal atoms in a single substitutional site of the solid rare gas is unlikely, with the possible exception of Ca/Xe. The luminescence of metal dimer bands has been recorded for Ba and Sr revealing very different behaviours. Resonance fluorescence with a lifetime of 15 ns is observed for the lowest energy transition of Sr{sub 2} while this transition is quenched in Ba{sub 2}. This behaviour is consistent with the absence of vibrational structure on the dimer absorption band in Ba{sub 2} indicating lifetime broadening arising from efficient relaxation to low-lying molecular states. More extensive 2D excitation-emission data recorded for the complex site structures present on the absorption bands of the atomic Ba and Sr systems will be presented in future publications.},
doi = {10.1063/1.4940688},
journal = {Journal of Chemical Physics},
number = 4,
volume = 144,
place = {United States},
year = {Thu Jan 28 00:00:00 EST 2016},
month = {Thu Jan 28 00:00:00 EST 2016}
}
  • Irradiation of atomic europium isolated in the solid rare gases, with low intensity laser excitation of the y{sup 8}P←a{sup 8}S resonance transition at ca. 465 nm, is found to produce singly charged europium cations (Eu{sup +}) in large amounts in xenon and in smaller amounts in argon. Confirmation of the formation of matrix-isolated Eu{sup +} is obtained from characteristic absorption bands in the UV and in the visible spectral regions. The luminescence produced with excitation of the cation bands is presented in greatest detail for Eu/Xe and assigned. Excitation of the 4f{sup 7}({sup 8}S{sub 7/2})6p{sub 3/2} absorption bands of Eu{supmore » +} between 390 and 410 nm produces emission which is quite distinct from that resulting from excitation of the 4f{sup 7}({sup 8}S{sub 7/2})6p{sub 1/2} absorption (430 to 450 nm) features. The latter consists of narrow, resolved emission bands with Stokes shifts ten times smaller than the former. The observed spectral differences are discussed in relation to the different spatial symmetries of the p{sub 3/2} and p{sub 1/2} orbitals in these j-j coupled (7/2, 3/2){sub J} and the (7/2, 1/2){sub J} levels. Møller-Plesset calculations are conducted to obtain the molecular parameters of the neutral Eu-RG and cationic Eu{sup +}-RG diatomics (RG = Ar, Kr, Xe). From the short bond lengths and the strong binding energies obtained for the Eu{sup +}-RG species, these values suggest the isolation of the ion in small, possibly interstitial sites especially in xenon. In contrast, but consistent with previous work [O. Byrne and J. G. McCaffrey, J. Chem. Phys. 134, 124501 (2011)], the interaction potentials calculated herein for the Eu-RG diatomics suggest that the neutral Eu atom occupies tetra-vacancy (tv) and hexa-vacancy (hv) sites in the solid rare gas hosts. Possible reasons for the facile production of Eu{sup +} in the solid rare gases are discussed. The mechanism proposed is that atomic europium is also acting as an electron acceptor, providing a temporary trap for the ionised electron in the matrices.« less
  • Three new compounds-Sr{sub 7.04(2)}Ga{sub 1.94(2)}Sb{sub 6}, Ba{sub 7.02(3)}Ga{sub 1.98(3)}Sb{sub 6} and Eu{sub 7.04(3)}Ga{sub 1.90(3)}Sb{sub 6}-have been synthesized from reactions of the corresponding elements using gallium as a metal flux. Their crystal structures (space group I4-bar 3d (No. 220), Z=2 with unit cell parameters: a=9.9147(9) A for the Sr-compound; a=10.3190(9) A for the Ba-compound; and a=9.7866(8) A for the Eu-compound) have been established by single-crystal X-ray diffraction. The structures are best described as Ga-stabilized derivatives of the hypothetical Sr{sub 4}Sb{sub 3}, Ba{sub 4}Sb{sub 3} and Eu{sub 4}Sb{sub 3} phases with the cubic Th{sub 3}P{sub 4} type. Such an inclusion of interstitialmore » Ga atoms in this atomic arrangement results in the formation of isolated [Ga{sub 2}Sb{sub 6}]{sup 14-} fragments, isoelectronic and isostructural with the [Sn{sub 2}Te{sub 6}]{sup 6-} anions in the K{sub 3}SnTe{sub 3} type, and allows for the attainment of a charge-balanced electron count. In that sense, the Sr{sub 4}Sb{sub 3}, Ba{sub 4}Sb{sub 3} and Eu{sub 4}Sb{sub 3} binaries, which are expected to be electron-deficient and are currently unknown, can be 'turned' into Sr{sub 7}Ga{sub 2}Sb{sub 6}, Ba{sub 7}Ga{sub 2}Sb{sub 6} and Eu{sub 7}Ga{sub 2}Sb{sub 6}, whose structures are readily rationalized following the Zintl concept. - Graphical abstract: Three new antimonides have been structurally characterized by single-crystal X-ray diffraction. Their structures are best described as derivatives of the body-centered cubic, anti-Th{sub 3}P{sub 4} type. Unlike the one-electron-deficient A{sub 4}Sb{sub 3} phases (A=Sr, Ba, Eu), the new, A{sub 7}Ga{sub 2}Sb{sub 6} compounds are Zintl phases with closed-shell configurations for both the cations and anions.« less
  • The interest in the formation and chemistry of main group alkoxides and aryloxides has undergone a renaissance over the last few years. There are many reasons for this surge of interest in such compounds, many of which until recently were poorly characterized or not known at all. One such stimulus is the discovery of superconducting ceramics containing alkaline earth ions. The reaction of barium metal granules with phenol and hexamethylphosphoramide (HMPA) in toluene at 25[degrees]C yields a novel eight-metal atom aggregate. The reaction of Sr[sub 3](OPh)[sub 6](HMPA)[sub 5] with barium metal and phenol yields a structurally related species. The twomore » aggregates have been characterized by IR and [sup 1]H, [sup 13]C, and [sup 31]P[l brace][sup 1]H[r brace] NMR spectroscopy and single-crystal X-ray studies and shown to consist to two square-based pyramidal M[sub 5]([mu][sub 5]-O) fragments sharing a common basal edge. The structure is completed by [mu][sub 3]- and [mu][sub 2]-phenoxide and terminal HMPA ligands. The selectivity for barium in the two polyhedral sites where the square-based pyramids are joined originates in the higher coordination number there. 20 refs., 2 figs., 3 tabs.« less