Transitions isomeric

K, electron capture IT, isomeric transition X, X-rays of indicated element (e.g., O-x, oxygen X-rays, and the type, K or L)... 

IT = isomeric transition, EC = electron capture, l3 = positron emission, and j3 = beta decay. 

In this group the most commonly used reaction is that of radiative neutron capture. Also here are to be found (n, 2 n) and (y, n) reactions, although very few studies have been done with these reactions, and isomeric transitions (although these may often be more profitably discussed along with electron capture reactions). 

An isotope effect seen in Sb03 by Maddock and Sutin was studied by Hall and Sutin , whose results are shown in Table 3. Again, phenyl radicals were cited as the likely means of reforming the bonds. It was pointed out that owing to the occurrence of isomeric transitions in both of these antimony isotopes, differences in the conversion coefficients could lead to the isotopic differences. 

Further work on nickelocene and cobaltocene was done by Ross , who synthesized the respective compounds using Ni, Ni and " Co, which decay be E.C., jS and a fully converted isomeric transition, respectively, all producing radioactive cobalt isotopes. The results showed retentions, after sublimation, of 84%, 83% and 80%, respectively. The composition of the unsublimable residue was largely CoCp2, except for the highly converted "Co, where only 30% CoCpj could be detected. This was interpreted as showing that by internal conversion the molecules are totally destroyed, by the same sort of argument as was used by Riedel and Merz . 

In the case of n-butene isomerization it was demonstrated (Figure 2) that the ideal micro-pore topology led to retardation of the C8 dimer intermediate and that the catalyst based on the ferrierite structure was close to optimal in this respect [1). For selective isodewaxing a one-dimensional pore structure which constrained the skeletal isomerization transition state and thereby minimized multiple branching such as the SAPO-11 structure was found to meet these criteria. Clearly, these are ideal systems in which to apply computational chemistry where the reactant and product molecules are relatively simple and the micro-porous structures are ordered and known in detail. 

The two Mossbauer levels of Pt, 99 keV and 130 keV, are populated by either EC of Au(fi/2 = 183 days) or isomeric transition of Pt(fi/2 = 4.1 days). Only a few authors, e.g., [323, 324] reported on the use of Pt, which is produced by thermal neutron activation of " Pt via " Pt(n, y) Pt. The source used in the early measurements by Harris et al. [322, 325] was carrier-free Au diffused into platinum metal. Walcher [326] irradiated natural platinum metal with deuterons to obtain the parent nuclide Au by (d, xn) reactions. After the decay of short-lived isotopes, especially Au(fi/2 = 6.18 days), Au was extracted with ethyl acetate, and the Au/Pt source prepared by induction melting. Buym and Grodzins [323] made use of (a, xn) reactions when bombarding natural iridium with... 

Isomers—Nuclides having the same number of neutrons and protons but capable of existing, for a measurable time, in different quantum states with different energies and radioactive properties. Commonly the isomer of higher energy decays to one with lower energy by the process of isomeric transition. 

Transition, Isomeric—The process by which a nuclide decays to an isomeric nuclide (i.e., one of the same mass number and atomic number) of lower quantum energy. Isomeric transitions (often abbreviated I.T.) proceed by gamma ray and/or internal conversion electron emission. 

De-excitation of 99mTc has specific features. This nuclide decays with a half-life of 6 hours, but its half-life varies slightly according to environmental conditions [30] or chemical states [31,32], Moreover, the emission probabilities of characteristic X-rays just after the isomeric transition 99mTc — "Tc are influenced by environmental factors [33] which result in a change of the K/VKoc X-ray intensity ratio [34],... 

Fig. 6. The low-lying level structure of "Tc and the relevant atomic transition close to the isomeric transition in energy (keV) [25]...

Isomerization Transition in (NaF)4 using the Wang-Landau Algorithm... 

I.T. is isomeric transition from an upper to a lower isomeric state. 

EC = electric capture IT = isomeric transition t extrapolated from ref. [53]... 

The formation of anhydrides 101 in the thermal decomposition reactions of TV-acyloxy-TV-alkoxyamides in non-polar mesitylene (Scheme 21, pathway (ii)) can thus be attributed to HERON migration of acyloxyl groups. However, the similarity of Eas for the two isomeric transition states raises the possibility that in these reactions some, or all of the ester might be generated by HERON migration of the alkoxyl substituent (Scheme 21, pathway (iii)). 

C. Steinbach, M. Famik, I. Ettischer, J. Siebers, and U. Buck, Isomeric transitions in size selected methanol hexamers probed by OH stretch spectroscopy. Phys. Chem. Chem. Phys. 8, 2752 2756 (2006). 

Fig. 4. A section of the energy surface, analogous to Fig. 3, for an isomeric transition. The values of the configurational coordinates about a and b correspond to the two isomeric forms of the molecule which are stable against small atomic displacements. The electronic energies for the two forms, namely Ea and E0, are assumed to be the same, although this need not necessarily be the case. This section of the energy surface is assumed to pass through the saddle point in the potential range separating the two minima a and b. The energy of the saddle point is E. ...

In our example of an isomeric transition then, we may conclude that the speed with which the reaction takes place in either direction is determined by the activation energies Qa and Qb. The larger these quantities are the slower the reaction in either direction will be. In the case shown in Fig. 4, Qa and Qb are assumed to be equal since Ea and Eb are taken as equal. This need not be the case and usually will not,... 

If the isomeric transition is taking place under conditions where the molecules cannot interact with one another or with the walls of the vessel in which they are contained other than in sueh a way as to transfer energy or momentum, the activation energy Qa and Qb will be determined entirely by the internal characteristics of the molecule and will be what might be termed natural constants of the system, analogous to the heat of formation. Thus under these conditions the reaction rates for the isomeric transitions will be fixed by the internal constitution of the molecules. At a given temperature the reaction rate can be changed... 

Fig. 5. A schematic representation of the influence of a catalyst on the energy surface in the ideal case. The full curve represents the normal energy curve, whereas the dotted curve represents the energy curve in the presence of the catalyst. Both curves are assumed to be sections through the saddle points. In this example the portions of the energy surface corresponding to the isomers a and b are practically unaffected however, the activated molecules are strongly attracted so that the activation energy for the isomeric transition is lowered. The activated molecule is still less stable than the isomers.

However, the barrier to rotation does not always predict the regioselectivity of the ene reaction of O2 with alkenes. As shown latef, it is the non-bonded interactions in the isomeric transition states that control product formation and barriers to rotation are rather irrelevant. The calculated rotational barrier values, with the HF-STO-3G method, for the allylic methyls in a series of trisubstituted alkenes, as well as the experimentally observed ene regioselectivity of a series of selective substrates, are shown in Table 9. ... 

Ke, the intramolecular excimer equilibrium constant under conditions where the dynamics or rotational Isomeric transitions is suppressed, is examined on the basis of the theory of macrocyclization [Flory, P. J.-, Suter, U. W. Mutter, M. J. Am. Chem. Soc. 1976, 98, 5733, 5740,5745], The conformational averages of the required moments and polynomials are calculated using their exact matrix generation method. The calculations can rationalize the appearance of a maximum near m = 15 In the 1 1 M that have been reported for pyrene-(CH2lrn-pyrene. In order to achieve this agreement, It is Imperative that the theoretical analysis incorporate the probability of a proper angular correlation of the two pyrene ring systems when the separation of their centers Is 0.35 nm. 

In the determination of cesium, the coal sample and cesium carrier are digested, and the perchlorate separation and ferric hydroxide scavenging precipitation are made as in the procedure for rubidium. Cesium is then separated from the remaining solution by precipitation of cesium bismuth iodide. The final separation is made by precipitation of cesium chloroplatinate, which is counted with a Geiger counter for the 0.66 MeV /T decay of 134Cs (U = 2.1 yr), or counted for the 0.13 MeV y-ray associated with the isomeric transition of 134mCs (t% = 2.9 hr). 

Mo( , y)99Mo(y3 — decay)99i"Tc(isomeric transition)99Tc... 

Example Problem Use the electromagnetic selection rules to identity the character of the isomeric transition from the hrst excited state at 0.439 MeV( + ) in 69Znm with the ground state ( ). Then calculate the Weisskopf single-particle rates for the allowed transitions. 

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