Ionization potentials condensed phase

Table III. Ionization Potentials (IP) of the Molecules and Atoms In Equilibrium with a Plutonium Dioxide Condensed Phase (1 eV molecule- - - 23.06 kcal mol- =...

The general requirement for charge transfer is that the transfer should occur from a molecule of higher ionization potential to a molecule of lower ionization potential that is, that the reaction be exothermic. In general, it is also accompanied by some vibrational excitation.43 In the condensed phase the ionization potential may be modified somewhat by collective effects but the gas phase value can be used to a first approximation to determine the reaction energetics. 

In the gaseous phase, an electron ejected from a molecule becomes free, and so for each filled electron level we have only one ionization potential. However, in the condensed phase an ejected electron can be in three different states free, quasi-free, and solvated. So the definition of the ionization potential becomes ambiguous. 

A large number of studies have been devoted to measuring the ionization potential in the liquid and the solid phases (see Refs. 179-181, 189, 190). Some of these results are presented in Table VII, from which one can see that for most substances V0 is negative, and so the ionization potential in the condensed phase is smaller than the photoemission threshold Eph. However, for some substances (for instance, for n-pentane, /i-decane, and neon), VQ is positive, meaning that in this case it is more advantageous, from the energy point of view, for an electron to make a transition into vacuum than to remain in a quasi-free state. 

The third class of organic donor molecules are a-donors, viz., alkanes and cycloalkanes. These substrates have inherently high ionization and oxidation potentials. Therefore, their radical cations are not readily available by photoinduced electron transfer, but typically require radiolysis and electron impact in the condensed phases or the gas phase, respectively. Thus, radical cations of simple alkanes (methane [206], ethane [207]) or unstrained cycloalkanes (cyclopentane, cyclohexane) [208] were identified and characterized following radiolysis in frozen matrices. In contrast, strained ring compounds have significantly lower oxidation potentials so that the radical cations of appropriate derivatives can be generated by photoinduced electron transfer. 

One other possible index for the resonance interaction in these systems is the 15N chemical shift of the enamine, whether as such30 or relative to that of the corresponding saturated amine305. It is a measure of the activation energy for twist about the C—NR1 2 bond, but it is less generally applicable than the former index based on the ionization potentials, even though it can be measured in the condensed phase where the basicity is to be determined. 

In Figure 5 (b), -ACo is 0.17 eV smaller than that in (a). This difference corresponds to the difference in ionization potential between DMA and AN in condensed phase. The reaction becomes faster as the temperature increases and the change is rather large at the slower part of the reaction than the fast part. 

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