Atom isolated

Fig. 6. Optical spectrum of Ir atoms isolated in solid Ar at 10-12 K, compared to the gas-phase atomic transitions of Ir. The stick heights correspond to reported oscillator strengths of gaseous Ir atoms (49).

Techniques other than UV-visible spectroscopy have been used in matrix-isolation studies of Ag see, for example, some early ESR studies by Kasai and McLeod 56). The fluorescence spectra of Ag atoms isolated in noble-gas matrices have been recorded (76,147), and found to show large Stokes shifts when optically excited via a Si j — atomic transition which is threefold split in the matrix by spin-orbit and vibronic interactions. The large Stokes shifts may be explained in terms of an excited state silver atom-matrix cage complex in this... 

Further investigation of the optical spectra of Cu, Ag, and Au atoms isolated in Ha, Oa, Na, and CH4 matrices has been reported. ... 

The absorption spectra of Zr atoms isolated in a variety of matrices have been reported. In addition, the diatomic molecule ZrN, prepared using a hollow cathode source and Na, was observed. Other work involving Na included the identification of ThN and Th(Na), and TaN in various matrices. 

Kniemeyer O, C Probian, R Rossello-Mora, J Harder (1999) Anaerobic mineralization of quaternary carbon atoms isolation of denitrifying bacteria on dimethylmalonate. Appl Environ Microbiol 65 3319-3324. 

Figure 4. Carbosilanes containing five to eight Si atoms, isolated by column chromatography and HPLC.

Figure 2. Comparison of the major emission bands of Ag atoms isolated in Ar, Kr, and Xe matrices. The ordinate represents emission intensity in arbitrary units, and the corresponding excitations are illustrated on the absorption spectra at the left. (Reproduced from Ref. 30. Copyright 1980, American Chemical Society.)...

Figure 4. Fluorescence spectra of Cu atoms isolated in solid Ar at 12 K (Cu/Ar 1/104) uncorrected for instrumental factors. The corresponding excitation wavelengths are indicated on the absorption spectrum shown at the upper left. (Reproduced from Ref. 34. Copyright 1982, American Chemical Society.)...

Six atomic isolated E6 entities are common and were observed in neutral S6 and Se6 as well as cationic Sg2+, Te62+ and Te64+. Moreover, the structures of several polymeric Te cations contain six-membered rings (see later section). 

Absorption spectra have been recorded for tantalum atoms isolated in an argon matrix at 4.2 K. A complex spectrum was observed between 228.8 and 504.1 nm which, with only a few exceptions, correlates with the transitions within the ground state observed for tantalum atoms in the gas phase. The... 

In bimetalUc systems PtSn-BM, it is possible to observe that a part of the Pt is alloyed with the metalUc Sn (PtSn, according to EXAFS results) and that the other part of the Pt is alloyed with metallic Pt atoms isolated from such an alloy. There also exists a Sn percentage of ionic nature (20-30%), probably placed in the metal-support interface. Scheme 6.1(b) gives an image of the catalytic surface for PtSn-BM. 

In the first case changes in metal-adsorbate bond strength are very small in the second case the effect of atom isolation is found to be comparable to band filling. Only with very large filling of the band does the heat of chemisorption decrease. 

Working with the density operator is a convenient alternative to using wavefunctions when dealing with a few-atom, isolated molecular system, insofar it suggests more efficient computational procedures or more consistent approximations, but it is not stricktly needed. The density operator is however essential in treatments of a many-atom system, when this interacts with a medium which constrains thermodynamical properties such as temperature or pressure, because the density operator incorporates statistical averages which would not be included in a treatment based on wavefunctions. 

The half-life of 181W has been re-investigated and a value of 120.95 + 0.02 days determined, which differs significantly from the currently accepted value 272 The u.v. absorption spectra of molybdenum atoms isolated in rare-gas matrices at 14 K have been correlated with similar gas-phase spectral data and assigned in spherical symmetry. Diffusion of the metal atoms in an Ar matrix was also studied and some tentative evidence obtained for dimer formation.273 The standard heat of vapourization of molybdenum has been determined274 as 689.3 kJ (g atom)-1. 

Ag° atoms isolated in the cubo-octahedral site of rare gas solids. The observation of multiple structure on the 2P 2S absorption and large red spectral shifts for the 2P - 2S emission of site I entrapped Ag° atoms, indicates that the guest-host interactions are markedly different for the 2S and 2P states and can be explained in terms of site I relaxation effects, using a vibronic coupling model similar to that described in detail for Ag° atom rare gas cage complexes (5). 

Discussion. Copper in Krypton. The absorption spectra of copper atoms Isolated in rare gas matrices have been extensively studied (15-25) and the triplet of bands at 310nm attributed to a number of different causes. These include (1) spin orbit splitting and static axial site distortion (17), (2) multiple matrix sites (18), (3) exciplex formation between the metal and a single matrix atom (19), (4) long range metal-metal interactions (2 ), and (5) Jahn-Teller (JT) effect resulting from matrix cage atom vibrations on the excited metal (21,22,23). The MCD of Cu atoms in the rare gas matrices has recently been reported (24,25) and the results interpreted as consistent with either the distorted site or JT hypotheses (39). 

Mesoporous tin-containing analogues of MCM-41 and tin oxide-modified me-soporous SBA-15 have also been characterized by Mossbauer spectroscopy (162,163). In the first case, the results suggest that tin was incorporated in the structure of the silicate and, in the second, they indicated that two types of supported tin species were formed, depending on the tin content. One would correspond to atomically isolated species stabilized in the wall of the pore and susceptible to reduction to Sn under reductive treatment conditions and the other to large oxide clusters distributed in the external pore structure. 

Lifetimes of emitting states of Fe, Co, and Ni atoms isolated in Ar and Kr matrices lie in the reuige 150-1250 jis. The role of the matrix euid the possibilities of magnetic dipole or vibrationally induced electric dipole mechanisms for emission have been discussed. Ligauid field excitation of [Fe(CNCH,),] in acetonitrile solution induces consecutive photosubstitution processes involving formation of the monosolvated intermediate [Fe(CNCH,) s(NCCH,) which subsequently gives... 

Summarizing the literature, one can cautiously conclude that so far stable formyl complexes have only been synthesized and isolated when the co ordinated centre was fully saturated. This might be an indication that with heterogeneous catalysts also such complexes can only be formed when the adsorption sites are isolated. This is the situation with, for example, ions or atoms isolated in a matrix of an inactive or much less active support or promoter, but not with bulk metals. As mentioned elsewhere, i.r. spectra obtained at slightly elevated temperatures with CO/Hj mixtures adsorbed on Cu/ZnO catalysts revealed two small bands which the authors ascribed to the frequently postulated formyl intermediates. 

Introduction.—The m.p. of 99.7% pure niobium has been measured as 2469 + 9°C. The crystal structure of p-tantalum appears to be isomorphous with that of P-uranium, and its X-ray powder diffraction pattern has been indexed in terms of a tetragonal unit cell. The absorption spectra of niobium atoms isolated in Ar, Kr, and Xe matrices at 14 K have been recorded. The absorptions observed in the u.v. region correlate well with those expected from known gas-phase data, but this was not the case for the visible and i.r. spectral regions. Spectral features observed upon annealing an Ar matrix containing Nb... 

The explanation for this drastic difference in behavior was finally advanced by Nernst in 1918. A small quantity of light suffices to break the chlorine molecule apart into two single chlorine atoms. One chlorine atom (much more active in itself than as part of a molecule) snatches a hydrogen atom from the hydrogen molecule, to form a hydrogen chloride molecule. The remaining hydrogen atom, isolated. 

By choosing a suitable atom density it is possible to place one atom on each potential minimum of the lattice. Such atoms isolated from their surrounding are excellent candidates for precise atomic clocks if one chooses a narrowband forbidden electronic transition to a metastable atomic state as clock transition. Since the atoms are (besides their zero-point motion) at rest no Doppler-effect contributes to line broadening or shift. There are intense investigations to realize an atomic clock... 

Isolated atoms Isolated atoms Isolated atoms Isolated atoms Isolated atoms Pairs... 

Fatty acids are long-chain carbo>ylic acids, usually of 12 or more carbon atoms, isolated from saponification of fats and oils (esters of glycerol). Draw fhe strucfure of each of the fatty acids named below and also determine its common name ... 

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