Resonance energy loss

The loss of energy due to damping, which can also include resonance energy loss, is proportional to the transverse velocity of the electron. 

Figure Bl.6.9 Energy-loss spectrum of La203 showmg O K and La M white Ime resonances at the La edge [H].

The tautomeric equilibria of these heterocycles always involve one or more non-aromatic tautomers. An important factor in determining the extent to which such non-aromatic tautomers are involved is the magnitude of the potential loss of resonance energy. 

Determination of concentration profiles from the raw data can be more complicated when protons are used as the incident particles. The energy loss ( dE/ die) is smaller for protons and straggling effects are more important. The observed profile A (AJ)) is a convolution of the actual concentration profile C x with a depth resolution function (x, Eq), which broadens with increasing x roughly as Jx- Hence, resolution deteriorates with depth. However, near-surface resolution for resonant profiling may be on the order of tens of A. 

The amino form is usually much more favored in the equilibrium between amino and imino forms than is the hydroxy form in the corresponding keto-enol equilibrium. Grab and XJtzinger suggest that in the case of a-amino- and a-hydroxy-pyrroles, structure 89 increases the mesomeric stabilization and thus offsets the loss of pyrrole resonance energy, but the increase due to structure 90 is not sufficient to offset this loss. Similar reasoning may apply to furans and... 

It is understandable that dihydro adducts should be formed by polycyclic compounds and not by benzene or pyridine, because the loss of aromatic resonance energy is smaller in the former than in the latter process, (c) When dibenzoyl peroxide is decomposed in very dilute solution (0.01 Af) in benzene, 1,4-dihydro biphenyl is produced as well as biphenyl, consistent with addition of the phenyl... 

The low yields of 6,6 -disubstituted-2,2 -bipyridincs recorded in Table I are probably the result of steric retardation of the adsorption of 2-substituted pyridines. This view is supported by the observation that 2-methylpyridine is a much weaker poison for catalytic hydrogenations than pyridine. On the other hand, the quinolines so far examined (Table II) are more reactive but with these compounds the steric effect of the fused benzene ring could be partly compensated by the additional stabilization of the adsorbed species, since the loss of resonance energy accompanying the localization of one 71-electron would be smaller in a quinoline than in a pyridine derivative. 

Substituted dibenzo[6,/]thiepins can be generated from thioxanthene derivatives by the rearrangement of carbocation 1. Compared with other possible cations, the tropylium ion type 1C is favored because of its resonance energy. Depending on the reaction conditions, the thiepin cation can react to give thiepins by loss of a proton, or by trapping a nucleophile, followed by elimination. 

Hence, nuclear resonance absorption of y-photons (the Mbssbauer effect) is not possible between free atoms (at rest) because of the energy loss by recoil. The deficiency in y-energy is two times the recoil energy, 2Er, which in the case of Fe is about 10 times larger than the natural line width F of the nuclear levels involved (Fig. 2.4). 

So far we have considered only the recoil-free fraction of photons emitted by the source. The other fraction (1 —/s), emitted with energy loss due to recoil, cannot be resonantly absorbed and contributes only as a nonresonant background to the transmitted radiation, which is attenuated by mass absorption in the absorber... 

Another, possibly more attractive rationale is that the loss of resonance energy on benzo-vinyl bridging makes this bonding mode energetically unattractive to the triplet state. 

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