Atomic samarium

Recently, a novel rf-laser double resonance method for optical heterodyne detection of sublevel coherence phenomena was introduced. This so-called Raman heterodyne technique relies on a coherent Raman process being stimulated by a resonant rf field and a laser field (see Fig.l(a)). The method has been applied to impurity ion solids for studying nuclear magnetic resonances at low temperature3 5 and to rf resonances in an atomic vapor /, jn this section we briefly review our results on Raman heterodyne detection of rf-induced resonances in the gas phase. As a specific example, we report studies on Zeeman resonances in a J=1 - J =0 transition in atomic samarium vapor in the presence of foreign gas perturbers. 

Fig. 1. Charge densities P r) [J P(r) dr = 1] of the 4f5,2, 5si relativistic Hartree-Fock calculations for the 4f 5d 6s configuration of atomic samarium.

MIR), requires the introduction of new x-ray scatterers into the unit cell of the crystal. These additions should be heavy atoms (so that they make a significant contribution to the diffraction pattern) there should not be too many of them (so that their positions can be located) and they should not change the structure of the molecule or of the crystal cell—in other words, the crystals should be isomorphous. In practice, isomorphous replacement is usually done by diffusing different heavy-metal complexes into the channels of preformed protein crystals. With luck the protein molecules expose side chains in these solvent channels, such as SH groups, that are able to bind heavy metals. It is also possible to replace endogenous light metals in metal-loproteins with heavier ones, e.g., zinc by mercury or calcium by samarium. 

When a uranium-235 atom undergoes fission, it splits into two unequal fragments and a number of neutrons and beta particles. The fission process is complicated by the fact that different uranium-235 atoms split up in many different ways. For example, while one atom of 292U is splitting to give isotopes of rubidium (Z = 37) and cesium (Z = 55), another may break up to give isotopes of bromine (Z = 35) and lanthanum (Z = 57), while still another atom yields isotopes of zinc (Z = 30) and samarium (Z = 62) ... 

Cooling of samples of crystalline samarium sulfide containing 22 atom% of gadolinium in the lattice to below — 153°C causes a near-explosive rearrangement to a powder form. This was attributed to changes in the lattice constants corresponding to a volume increase of 7.5%. 

The Sm-N distances are consistent with single a bonds suggesting the presence of a (C H NNC.H dianion. However, the 1.25(1) a NN distance is the same" as tire N=N double bond distances in a variety of azobenzene structures. The molecule also contains distorted N-C (phenyl) distances, which are stretched from a normal 1.42 8 distance to 1.56-1.61 8. In addition, the samarium atoms are displaced asymmetrically such that both come within 2.29-2.34 8 of the ortho hydrogens of a single phenyl ring in a bonafide agostic (6<0 Sm-H interaction. The ability of Sm(II) to structurally distort azobenzene in this way is remarkable. 

The crystal structure of the 1 2 adduct 145 obtained by the reaction of [Cp SmH]2 with MMA was determined by X-ray analysis. One of the two monomer units is in the O-enolate form and the other unit coordinates to the samarium atom by the carbonyl group. A comparison between 145 and the... 

In the presence of samarium(II) iodide, A-(2-iodobenzyl)dialkylamines 347 react with electrophiles at an a-carbon atom to yield deiodinated products by way of intermediate samarium compounds 348. Thus TV-(2-iodobenzyl)diethylamine and pentan-3-one afford the hydroxy amine 349 and 7V-(2-iodobenzyl)pyrrolidine and propyl isocyanate give the amide 350390. 

Kretschmer et al. have recently described the ability of 12 CpSmCl2 traits to form a neutral samarium-based shell, [Cpi2Sm12( t3-Cl)24], in which 12 samarium atoms... 

Europium - the atomic number is 63 and the chemical symbol is Eu. The name derives from the continent of Europe . It was separated from the mineral samaria in magnesium-samarium nitrate by the French chemist Eugene-Anatole Demar9ay in 1896. It was also first isolated by Demar ay in 1901. 

Samarium - the atomic number is 62 and the chemical symbol is Sm. The name derives from the mineral Samarskite, in which it was found and which had been named for Colonel von Samarski , a Russian mine official. It was originally discovered in 1878 by the Swiss chemist Marc Delafontaine, who called it decipium. It was also discovered by the French chemist Paul-Emile Lecoq de Boisbaudran in 1879. In 1881, Delafontaine determined that his decipium could be resolved into two elements, one of which was identical to Boisbaudran s samarium. In 1901, the French chemist Eugene-Anatole Demar9ay showed that this samarium earth also contained europium. 

The monoclinic form of Sm20s (B-form) contains (66) three types of samarium atoms. Two coordination polyhedra are distorted NbF t5 pe, while the third samarium may be described as hexacoordinated with a very long (3.12 A) M—O distance. This seventh oxygen is too far away to be included in the primary coordination sphere of Sm(III). 

Important is the use of light rare earth elonents for production of hard magnetic materials. Most prominent are alloys of samarium with cobalt in the atomic ratio 1 5 or 2 17. It may also be assumed that in further development of these materials on a larger scale that praseodymium, neodymium, lanthanum and also individual heavy rare ecu h elements will be used to achieve particular effects. Interesting is the development of magnetic bubble memories based on gadolinium-galliiimrgarnets. 

Guided by Marks s report of the samarium-catalyzed hydroboration of alkenes, Molander has developed a samarium-catalyzed protocol for the cyclization/hydroboration of unfunctionalized 1,6-dienes. In an optimized procedure, reaction of 1,5-hexadiene and l,3-dimethyl-l,3-diaza-2-boracyclopentane catalyzed by Gp 2Sm(THF) in toluene at room temperature for 18 h followed by oxidation gave hydroxymethylcyclopentane in 86% yield (Equation (70) R = H, n — ). The transformation was stereoselective, and Sm-catalyzed cyclization/hydroboration of 2-phenyl-1,5-hexadiene followed by oxidation formed /ra/ i--l-hydroxymethyl-2-phenylcyclopentane in 64% yield (Equation (70) R = Ph, n = ). The samarium-catalyzed reactions was also applicable to the synthesis of hydroxymethylcyclohexanes (Equation (70), n=X) but tolerated neither polar functionality nor substitution on the alkenyl carbon atoms. 

Europium, like all other rare-earth elements, generally forms compounds in which the metal atoms lose three electrons to become ions with three positive charges. This type of europium ion can emit light in the richest red part of the visible spectrum, when suitably stimulated by an energy source. But, unlike the other lanthanides (with the exception of samarium), europium also... 

Kleinerman and co-workers (158) reported an enhancement of fluorescent yield of chelated lanthanide ions by Lewis bases. They observed that in liquid, plastic, and glassy solutions containing terbium europium, and samarium chelates, the use of Lewis bases accomplishes the same effect as substituting deuterium for hydrogen. Not all bases, however, are equally effective. The molecular size of the base does not appear to be particularly important, since strong enhancement effects can be obtained with both bulky and small molecules. The nature of the atom of the base having the unshared electron pair is not a determining factor in the enhancement phenomenon. 

Noxon calculated the rate constant of O( D) quenching by 02 on the basis of unit quantum yield and of the equilibrium concentration of 0( >) atoms. His value of 6 x 10 11 cm3 molec"1 sec-1 agrees well with 7 x 10"11 cm3 molec"1 sec" 1 obtained independently (456), indicating that the assumption of unit quantum yield may be justified. Below 1332 A the production of O( S) is energetically possible. Filseth and Welge (348) have observed an emission at 5577 A due to the transition O( S)- O( D) in the flash photolysis of 02 below 1340 A. The intensity is so weak that Xe has to be added to induce the transition. No quantum yield of O(. S) production has been measured. Recently Stone et al. (937) have measured the llight time ofO atoms produced in the Hash photolysis of the molecular beam of 02 in the vacuum ultraviolet. The O atoms are detected by the chcmiionization reaction with samarium. The technique is similar to the one described in Section II 4.1. 

Atomic number Symbol Element 21 Sc Scandium 39 Y Yttrium 57 La Lanthanum 58 Cfc Cerium 59 Pi Praseodymium 60 Nd Neodymium 61 Pm Promethium 62 Sm Samarium 63 Eu Europium 64 Gd Gadolinium 65 Tb Terbium 66 Dy Dysprosium 67 Ho Ilolmium 68 Er Erbium 69 Tm Thulmm 70 Yb Ytterbium 71 Lu Lutetium... 

A reaction of dibromoacetic acid with different aldehydes promoted by Sml2, followed by an elimination reaction also promoted by samarium diiodide, affords ( > ,/l-unsaturalcd carboxylic acids with total stereoselectivity (Scheme 8).42 A mecha- (g) nism that involves chelation of the Sm(III) centre with the oxygen atom of the alcohol group through a six-membered chair-like transition state has been described. 

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