Molecule , anion states

Fig. 10. The emerging picture of electronically nonadiabatic interactions of NO molecule scattering at a metal surfaces. Transition from the ground electronic state to an anionic state which is strongly attractive to the metal surface can be accomplished by high translational energy when vibrational excitation is low (black trajectory). When vibrational motion is highly excited, even low translational energies allow transition of the anionic state (red trajectory). Recently, Monte-Carlo wavepacket calculations have been carried out which tend to support this picture.63...

This striking result can be qualitatively understood as related to CB DOS-influenced changes in the 02 anion lifetime [118]. For a diatomic molecule with R as the internuclear coordinate, a transient anion state is described in the fixed nuclei limit [123,124] by an energy and i -dependent complex potential Vo i R,E ) = Fd(2 ) + A( i)—l/2 T( i), where Va R) = a R) + is the potential energy curve of the discrete state, Vg(R) is the... 

Figure 20-3. Electron binding energies for molecule M in anionic state are defined pictorially in a representation of the potential energy surfaces of the neutral molecule (M) and anion radical (M ) with the lowest vibration energy level shown for each. During a vertical process, the geometry remains unchanged but for the adiabatic process structural relaxation occurs. Thus the VDE (vertical detachment energy) and VEA (vertical electron affinity) represent the upper and lower bounds to the adiabatic electron affinity (AEA)...

Resonant Electron Scattering and Anion States in Polyatomic Molecules... 

Photoelectron spectroscopy (PES) Q, and more recently electron transmission spectroscopy (ETS) (3, 4) have provided much information on the cation and anion states, respectively, of many hydrocarbons. Within the context of the Koopmans Theorem (KT) approximation, the cation states can often be associated with the filled orbitals and the anion states with the unfilled orbitals of a molecule. In this sense these two methods are complementary. However there are important distinctions between these two spectroscopic methods which arise in part from the very different lifetimes of the anions and cations. 

The energies of the NISs in Table 5 were determined from electron scattering experiments and refer to isolated molecules and to anionic states reached in the very initial step of the electron-molecule interaction. Although these show that the ir-electron affinity of the isolated molecules of these compounds are negative, they do not preclude the possibility of positive EA values in relaxed states or in non-isolated molecule environments. For strongly electron withdrawing substituents (e.g., NO.) the parent molecule (e.g. C.H.NO.) has a positive (>0.5% eV) 2J EA and forms long-lived (t > zO x 10 sec) ( ) parent... 

Giordan, J. C., J. H. Moore, and J. A. Tossell (1986). Anion states of organome-tallic molecules and their ligands. Acc. Chem. Res. 19, 281-86. 

In the excited singlet state the ionization potential of the molecule is reduced, and the excited electron is more easily removed compared to the ground state. This process of photoionization is also more likely to occur if higher energy UV radiation is used (i.e., wavelengths less than 300 nm) and if the drug molecule is in its anionic state. An example is naproxen in aqueous solution at pH 7, where the process of decarboxylation occurs and a neutral radical is formed (11), Reaction 7 ... 

In the first two parts of this chapter, electron transfer (ET) from atomic donors, e.g., alkali metals or the iodine anion, to an accepting unit composed of simple molecular or atomic solvents was discussed. It was demonstrated that even for a molecule without a stable anionic state or large dipole moment, e.g., water and ammonia, an ensemble of a relatively small number of the molecules can act as an electron acceptor. In the case of the solvated alkali metal atom clusters, ET takes place spontaneously as the number of solvent molecules increases, while the ET in the solvated 1 clusters is induced by photoexcitation into the diffuse electronic excited states just below the vertical detachment thresholds. These ET processes in isolated supermolecular systems resemble the charge delocalization phenomena in condensed phases, e.g., excess-electron ejection from alkali metals into polar solvents and the charge transfer to solvent in a solution of stable anions. 

The classic aromatic systems are planar molecules. Solid-state structural data have been obtained only for heavily substituted arsenic derivatives and for the borabenzene anion in a transition metal complex. The following data were obtained for these systems (1, 171, 303) ... 

The biochemical applications involve the electronic nature of the components of DNA and proteins, especially the charge distributions, electron affinities, and gas phase acidities of purines and pyrimidines and amino acids. The role of electron reactions in diverse areas such as cancer, electron conduction, and sequence recognition all depend on fundamental energetic properties such as electron affinities and solution energies. We explain nonadiabatic experimental data from radiation chemistry by excited anionic states of biological molecules [24],... 

In electron bound complexes of C60 with aromatic hydrocarbons, the intensity of the aromatic hydrocarbon anion from collisional ionization is larger than that for the aromatic hydrocarbon. However, it is known that the adiabatic electron affinities of the aromatic hydrocarbons are significantly lower than that of C60. In these cases the relative intensities were attributed to a localized anion. When the benzanthracene and phenanthrene electron bound dimer is dissociated, the intensity of the phe-nanthrene anion is only about one-half that of the benzanthracene anion, while the electron affinity of benzanthracene is 0.72 eV and that for phenanthrene is 0.30 eV. The experimental data cannot be disputed. The ion ratio gives a AEa of 0.08 eV or the Ea of benzanthracene = 0.30 + 0.08 = 0.38(10) eV. Therefore, some other explanation must be presented. In the case of C60 excited anion states are observed and three degenerate LUMO + 1 are calculated with positive electron affinities. Benzanthracene has an excited-state MO at 0.38 eV that gives an Ea of 0.38 eV. Just as C60 has multiple LUMOs, so also does benzanthracene. Because the collisional ionization values are the most recent, they are returned by a search of the NIST tables for CH molecules. These values are fisted in Chapter 10 [61-63]. 

The electron affinities Ea of the main group atoms are the most precisely measured values. Recall that the Ea is the difference in energy between the most stable state of the neutral and a specific state of a negative ion. It was once believed that only one bound anion state of atoms and molecules could exist. However, multiple bound states for atomic and molecular anions have been observed. This makes it necessary to assign the experimental values to the proper state. The random uncertainties of some atomic Ea determined from photodetachment thresholds occur in parts per million. These are confirmed by photoelectron spectroscopy, surface ionization, ion pair formation, and the Born Haber cycle. Atomic electron affinities illustrate the procedure for evaluating experimental Ea. 

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