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51.
Bragg cut-off for
plane of polycrystalline beryllium of various lengths of 300 and 116 K has been measured with an energy resolution of 5 μeV.
The natural width of the cut-off is 12.5±1.5 μeV, independent of temperature and length of beryllium and also of physical
characteristics and certain metallurgical treatments of the powder. Such blocks of beryllium would be suitable for designing
a ΔT-window spectrometer with resolution ⩾20 μeV. Bragg cut-offs corresponding to (0002) and
planes of beryllium have been separated for the first time. These can also be used for producing additional energy windows
in a ΔT-window spectrometer, thus increasing its efficiency.
Paper entitled ‘ΔT-window spectrometer’ will appear in the November issue of Pramana. 相似文献
52.
53.
Eu3+ and Eu2+ in Oxides of the Composition MBeLn2O5: SrBeEu2O5 and EuBeNd2O5 Single crystals of (I): SrBeEu2O5 and (II): EuBeNd2O5 were prepared by CO2-LASER (I) in air and plasma torch (II) technique in H2 atmosphere. X-ray investigations led to orthorhombic symmetry, space group D-Pnma; (I): a = 9.488, b = 7.156, c = 6.495 Å; (II): a = 9.534, b = 7.225, c = 6.544 Å, Z = 4. Sr2+ and Eu3+ as well as Eu2+ and Nd3+ are in statistical distribution within a Kagomé framework. Both compounds are discussed with respect to the monoclinic form of MBeLn2O5. 相似文献
54.
Dr. Lewis R. Thomas-Hargreaves Chantsalmaa Berthold William Augustinov Dr. Matthias Müller Dr. Sergei I. Ivlev Dr. Magnus R. Buchner 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(35):e202200851
Diphenylberyllium [Be3Ph6] is shown here to react cleanly as a Brønsted base with a vast variety of protic compounds. Through the addition of the simple molecules tBuOH, HNPh2 and HPPh2, as well as the more complex 1,3-bis-(2,6-diisopropylphenyl)imidazolinium chloride, one or two phenyl groups in diphenylberyllium were protonated. As a result, the long-postulated structures of [Be3(OtBu)6] and [Be(μ-NPh2)Ph]2 have finally been verified and shown to be static in solution. Additionally [Be(μ-PPh2)(HPPh2)Ph]2 was generated, which is only the second beryllium-phospanide to be prepared; the stark differences between its behaviour and that of the analogous amide were also examined. The first crystalline example of a beryllium Grignard reagent with a non-bulky aryl group has also been prepared; it is stabilised with an N-heterocyclic carbene. 相似文献
55.
Christopher F. Mallinson James E. Castle John F. Watts 《Surface and interface analysis : SIA》2015,47(10):994-995
Herein, we report the construction of a Wagner chemical state plot for beryllium containing the following: metallic, oxide, nitride and carbide forms of beryllium by combining electron beam‐induced AES and XPS data. AES and XPS values were collected from metallic beryllium mechanically abraded in vacuum, bulk and native beryllium oxide and homogeneous secondary‐phase beryllium nitride and beryllium carbide inclusions. XPS data for beryllium nitride and carbide were obtained from the literature. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
56.
《Journal of computational chemistry》2017,38(1):37-43
The accurate potential energy surface of beryllium monohydroxide, BeOH, in its ground electronic state has been determined from ab initio calculations using the coupled‐cluster approach in conjunction with the correlation‐consistent core‐valence basis sets up to septuple‐zeta quality. The higher‐order electron correlation, scalar relativistic, and adiabatic effects were taken into account. The BeOH molecule was confirmed to be bent at equilibrium, with the BeOH angle of 141.2° and the barrier to linearity of 129 cm−1. The vibration‐rotation energy levels of the BeOH and BeOD isotopologues were predicted using a variational approach and compared with recent experimental data. The results can be useful in a further analysis of high‐resolution vibration‐rotation spectra of these interesting species. © 2016 Wiley Periodicals, Inc. 相似文献
57.
Sudip Pan Said Jalife R. Mahesh Kumar Dr. Venkatesan Subramanian Prof. Gabriel Merino Prof. Pratim K. Chattaraj 《Chemphyschem》2013,14(11):2511-2517
The noble gas binding ability of CN3Be3+ clusters was assessed both by ab intio and density functional studies. The global minimum structure of the CN3Be3+ cluster binds with four noble‐gas (NG) atoms, in which the Be atoms are acting as active centers. The electron transfer from the noble gas to the Be atom plays a key role in binding. The dissociation energy of the Be? NG bond gradually increases from He to Rn, maintaining the periodic trend. The HOMO–LUMO gap, an indicator for stability, gives additional insight into these NG‐bound clusters. The temperature at which the NG‐binding process is thermodynamically feasible was identified. In addition, we investigated the stability of two new neutral NG compounds, (NG)BeSe and (NG)BeTe, and found them to be suitable candidates to be detected experimentally such as (NG)BeO and (NG)BeS. The dissociation energies of the Be? NG bond in monocationic analogues of (NG)BeY (Y=O, S, Se, Te) were found to be larger than in the corresponding neutral counter‐parts. Finally, the higher the positive charge on the Be atoms, the higher the dissociation energy for the Be? NG bond becomes. 相似文献
58.
建立ICP–AES法测定铍钴铜合金中主量元素铍、钴含量的方法。将试样用硝酸、盐酸溶解,在钇内标存在的情况下以等离子体光源激发,并分别选择分析谱线Be 313.1 nm,Co 228.6 nm进行光谱测定。铍、钴含量在0~5%范围内与光谱强度线性相关,铍、钴两元素线性相关系数分别为0.999 18,0.999 91;检出限分别为0.000 12%,0.001 1%;测定结果的相对标准偏差为0.25%~4.59%;回收率在96%~102%之间。该方法操作简单实用,可同时测定铍、钴两元素,测定结果准确可靠。 相似文献
59.
Dr. M. Merced Montero‐Campillo Prof. Manuel Yáñez Dr. Al Mokhtar Lamsabhi Prof. Otilia Mó 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(18):5309-5316
The most stable complexes between squaric acid and its sulfur‐ and selenium‐containing analogues (C4X4H2; X=O, S, Se) with BeY2 (Y=H, F) were studied by means of the Gaussian 04 (G4) composite ab initio theory. Squaric acid derivatives are predicted to be very strong acids in the gas phase; their acidity increases with the size of the chalcogen, with C4Se4H2 being the strongest acid of the series and stronger than sulfuric acid. The relative stability of the C4X4H2 ? BeY2 (X=O, S, Se; Y=H, F) complexes changes with the nature of the chalcogen atom; but more importantly, the formation of the C4X4H2 ? BeF2 complexes results in a substantial acidity enhancement of the squaric moiety owing to the dramatic electron‐density redistribution undergone by the system when the beryllium bond is formed. The most significant consequence of this acidity enhancement is that when BeF2 is replaced by BeH2, a spontaneous exergonic loss of H2 is observed regardless of the nature of the chalcogen atom. This is another clear piece of evidence of the important role that closed‐shell interactions play in the modulation of physicochemical properties of the Lewis acid and/or the Lewis base. 相似文献
60.
Dr. Andreas Hermann Prof. Dr. N. W. Ashcroft Prof. Dr. Roald Hoffmann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(13):4184-4197
We explore ground‐state structures and stoichiometries of the Be? B system in the static limit, with Be atom concentrations of 20 % or greater, and from P=1 atm up to 320 GPa. At P=1 atm, predictions are offered for several known compounds, the structures of which have not yet been determined experimentally. Specifically, at 1 atm, we predict a structure of R$\bar 3$ m symmetry for the compound Be2B3, seen experimentally at high temperatures, which contains interesting BeBBBBe rods; and for the compound BeB4 we calculate metastability with respect to the elements with a structure similar to MgB4, which is quickly replaced as the pressure is elevated by a Cmcm structure that features 6‐ and 4‐membered rings in B cages, with Be interstitials. For another high‐temperature compound, Be2B, we confirm the CaF2 structure, but find a competitive and actually slightly more stable ground‐state structure of C2/m symmetry that features B2 pairs. In the case of BeB2, a material for which the stoichiometry has been the subject of debate, we have a clear prediction of a stable F$\bar 4$ 3m structure at P=1 atm. It has a diamondoid structure that is based on cubic (lower P) or hexagonal (higher P) diamond networks of B, but with Be in the interstices. This Zintl structure is a semiconductor at low and intermediate pressures. At higher pressures, BeB2 dominates the phase diagram. In general, the Zintl–Klemm concept of effective electron transfer from the more electropositive ion and bond formation among the resulting anions has proven useful in analyzing the structural preferences of many compositions in the Be? B system at P=1 atm and at elevated pressures. An unusual feature of this binary system is that the 1:1 BeB stoichiometry never appears to reach stability in the static limit, although it comes close, as does Be17B12. Also stable at high pressures are stoichiometries BeB3, BeB4, and Be5B2. 相似文献