An x-ray and neutron diffraction analysis of lithium hydride

Calder, R.; Cochran, William G.; Griffiths, D. C.; Lowde, R. D.

doi:10.1016/0022-3697(62)90522-x

Cited by 94 publications

(30 citation statements)

References 23 publications

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“…On the other hand, high reactivity makes it difficult from the experimental point of view and, until lately, the supporting experimental data have been scant compared with the wealth of theoretical results and predictions. For 0108-7673/92/010046-15503.00 example, until 1986, the only neutron and X-ray diffraction results were those obtained by Calder, Cochran, Griffiths & Lowde (1962) in their classical work.…”

Section: Introductionmentioning

confidence: 99%

Evidence on the breakdown of the Born-Oppenheimer approximation in the charge density of crystalline 7LiH/D

Vidal-Valat¹,

Vidal²,

Kurki-Suonio³

et al. 1992

Acta Cryst Sect A

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Accurate X-ray diffraction data on LiH and LiD measured at three different temperatures are analysed in terms of multipolar radial densities searching for phenomenological indications on the nature of bonding. The average spherical charge density around the atomic positions shows typical features of an ionic crystal. The central peaks are slightly contracted compared with superimposed free ions. The Li + peak contains, however, a small but significant excess of electrons, and the H-/D-peak is low and diffuse. Li + is spherical and its Debye-Waller parameters agree with the neutron diffraction values obtained by Vidal& Vidal-Valat [Acta Cryst. (1986), B42, 131-137]. This indicates that, within the experimental accuracy, Li + is rigid. The non-spherical multipoles are significantly stronger in the hydrogen than in the deuterium derivative. They accumulate charge along the (100) directions giving a phenomenological indication of 'long-distance covalency' of H-H and D-D bonding with Li ÷ ions embedded in the middle but not contributing to the covalency. The significant deviation of the charge distribution of the anion in LiH from that in LiD indicates breakdown of the Born-Oppenheimer approximation due to coupling of the vibrations and the electronic states, which is much stronger in LiH. This is the first case -and probably the only possible -where such a breakdown can be seen by X-ray diffraction.

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Section: Introductionmentioning

confidence: 99%

Evidence on the breakdown of the Born-Oppenheimer approximation in the charge density of crystalline 7LiH/D

Vidal-Valat¹,

Vidal²,

Kurki-Suonio³

et al. 1992

Acta Cryst Sect A

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“…The effects of error in the scattering factors of hydrogen on the temperature factors derived from the refinement have been discussed by Calder, Cochran, Griffith & Lowde (1962) who compared X-ray and neutron resuits to show that in crystals of LiH the hydrogen ion suffers contraction compared to the free atom. Jensen & Sundaralingam (1964) found evidence for contraction of the bonded hydrogen atom by comparing the isotropic thermal parameters of the hydrogen to Bi~o of the atoms to which they are bonded.…”

Section: Comparandon Of Thermal Parametersmentioning

confidence: 99%

Sucrose: X-ray refinement and comparison with neutron refinement

Hanson¹,

Sieker²,

Jensen³

1973

Acta Crystallogr Sect B

122

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The structure of sucrose has been refined with Mo K~ diffractometer data collected from two crystals to a sin 0/2 limit of 0"81 A -1. 3280 reflections were measured of which 3098 were greater than 2o'. The structure has been refined with low-angle data (sin 0/2 < 0"64 A-1), high-angle data (sin 0/2 > 0.64 A-1) and all the data, and the results compared with the very precise neutron-diffraction results of Brown & Levy. The final R indices are 0.025, 0.029 and 0.029 respectively for the X-ray data. The C-O bond lengths from refinements of low-angle and all data are longer and thermal parameters greater than those from the neutron data. The thermal parameters for the nonhydrogen atoms obtained from the high-angle refinement, however, are not significantly different from the neutron values. Use of bonded hydrogen atom scattering factors of Stewart, Davidson & Simpson [J. Chem. Phys. (1965). 42, 3175-3187] led to thermal parameters for hydrogen bonded to oxygen and for hydrogen bonded to carbon which were respectively 0.3(3) A s greater and 1 "9(1) A 2 less than those from the neutron results. Residual electron-density maps based on neutron coordinates and X-ray data showed the expected bond and lone pair features much more clearly than maps based on the coordinates obtained from refinement of high sin 0 X-ray data.

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“…However, their ionic properties are weaker than for alkali halide crystals because the electronic affinity for hydrogen is weaker than for halide ions [I]. Moreover, X-ray and neutron diffraction [2] as well as electron diffraction [3] experiments have shown the existence of a certain part of covalent bonding at least in the case of LiH. Possibly, the presence of covalent bonding is one of the reasons why lithium hydride isotopes exhibit stronger second-order Raman scattering [4] than alkali halides and why the optical band gap of LiH (z 5 eV [5]) is comparable to the ionization energy of a Li atom.…”

Section: Introductionmentioning

confidence: 99%

The Comparative Studies of Low‐Temperature Nearest‐Neighbour Distances in Alkali Hydride Crystals

Tyutyunnik

1995

Physica Status Solidi (b)

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The numerical analysis demonstrates that at low temperatures the change in lattice parameter between the alkali hydride salts is related only to the difference between the radii of the "alkali atoms" which have the same sizes as those in the alkali metals with body-centred cubic structure. There is no isotope effect on the size of particles constituting an alkali hydride crystal.A H~J I M~ AaHHbIx neMoHcTpapyeT, YTO npr? HHJKHX TeMnepaTypax pasnarlre B napaMerpe pememn MeXAy COJIRMH 4eJIOYHbIX rnApr?AOB CBIIJaHO TOJIbKO C pa3JIHYHeM MeXAy PanIlycaMH G~eJIOYHbIX BTOMOB)), KOTOpbIe o 6 n a n a~n TaKllMr? Xe pa3MepaMr?, KaK aTOMbI B UWIOqHbIX MeTaJlnaX C 06aeMHO-ueHTpr?pOBaHHOfi KY6HYeCKOfi CTpyKTypO%. k330TOnHbIe BJIIIXHHR Ha YaCTH~bI,o6pasym~r?e KpHcTann wenomoro rr?Apr?aa, OTCYTCTBYWT.

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An x-ray and neutron diffraction analysis of lithium hydride

Cited by 94 publications

References 23 publications

Evidence on the breakdown of the Born-Oppenheimer approximation in the charge density of crystalline 7LiH/D

Evidence on the breakdown of the Born-Oppenheimer approximation in the charge density of crystalline 7LiH/D

Sucrose: X-ray refinement and comparison with neutron refinement

The Comparative Studies of Low‐Temperature Nearest‐Neighbour Distances in Alkali Hydride Crystals

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