Oxygen atom, electron affinity molecule

Amines possess a pair of p-electrons on the nitrogen atom. The nitrogen atom has a low electron affinity in comparison with oxygen. Therefore, amine can be the electron donor reactant in a charge-transfer complex (CTC) in association with oxygen-containing molecules and radicals. It will be shown that the formation of CTC complexes of amines with peroxyl radicals is important in the low-temperature oxidation of amines. 

At a rough surface of a solid without electron defects, the molecules of oxygen do not dissociate faster into their atoms than in air because no electron interchanges take place. In contrast to the homogeneous gas phase, the thermodynamic situation at the surface of a suitable catalyst is quite different. Due to the electron affinity of oxygen, the electron can be transferred to the chemisorbing oxygen... 

Fig. 1. Energy scheme of chemisorption and physical adsorption of oxygen vs. distance from the surface according to Lennard-Jones. E tt is the electron affinity of atomic oxygen, Eo the dissociation energy of oxygen molecules, Ecu the chemisorption energy, and Exot the activation energy. Position A is that of physically adsorbed O2, and position B is that of chemisorbed O".

The electron affinity of the metal surface is low in comparison with the tendency of the foreign molecule to receive electrons. This tendency is particularly high if the electron shell of the adsorbed molecule is incomplete (e.g. as in an oxygen atom) or if the bond of the atoms in the molecule is affected by an asymmetric electron shift (e.g, as in the molecules of nitrous oxide or carbon monoxide). In such cases the metal electrons become part of the electron shell of the foreign molecule. 

The spontaneous oxidation of molecular oxygen and of atomic xenon, each of which has a first ionization potential of 281 kcal. mole , by platinum hexafluoride, has estabhshed the remarkable oxidizing power of the hexafluoride. None of the other third-transition-series hexafluorides will oxidize these species. Since it is well established - that the platinum hexafluoride-oxygen adduct is the salt Oj+[PtFe] , the lattice energy of which is estimated, employing Kapustinskii s second equation to be 125 kcal. moIe, the electron affinity of the PtF, molecule is required to be >156 kcal. mole, to ar count for the observed exothermic reaction [Pg.244]

Interactions at room temperature When CO is first introduced (Fig.l), a increases irtfantaneously and then remains independent of P 0. The fact that a does not decrease means that CO does not dissociate on titania nor at the interface, otherwise the filling of anionic vacancies by atomic oxygen (Eq,-6) would have decreased substantially a by consuming free electrons. The sharp initial increase, on the contrary, shows that CO chemisorb on Pt with a donor effect probably due to the creation of dipoles as proposed for H. chemisorption which renders ohmic the electrical contact between the metal and its semiconductor support (26, 17, 28)Accordlng to these authors, the creation of a dipole layer decreases the work function of the metal which approaches the electron affinity of the semiconductor, thus suppressing the Schottky barrier. Presently CO adsorbs as a donor molecule on Pt decreasing 0, which allows elec-... 

Here, A is the affinity between oxygen atom and electron (p is the work function of electron determined by the level position of chemical potential D is the dissociation energy of oxygen molecule and W is the interaction energy of the formed ion with catalyst. The latter value is determined by the properties of the adsorbed substance and of a catalyst, and should, in general, depend on the position of the adsorbed particle on the surface. 

Finally, we stress the twofold role of the oxygen atoms for the substrate interaction. On the one hand, direct bonds with the substrate are formed. On the other hand, the electronegative anhydride groups increase the eleetron affinity of the 7i-electron system towards metal electrons, as the comparison with the perylene molecule (2 in Figure 12.2) shows perylene interaets much more weakly with Ag(lll) and at room temperature forms a orientationally disordered layer [48]. A third role of the oxygen atoms, namely their participation in intermolecular interactions, will be discussed briefly in Section 12.3. 

---