Partial charge exchange

Partial charge-exchange reaction. Synonymous with partial charge-transfer reaction. 

In the case of partial charge exchange between a doubly charged ion and a molecule,... 

The difference between RE and RE has been assumed to be about 2 eV/ Only partial charge exchange has been considered, but not all possible transitions have been included. 

The first RE is of limited interest, as many molecules cannot absorb an energy of the order of 54 eV in an ionization process. This is probably the case for all hydrocarbons, as they are built up of carbon atomic orbitals with orbital energies of the order of 300, 24, and 13 eV, and hydrogen atomic orbitals at 13 eV. As the third RE is too low for ionization of most molecules, the electron will enter the 2s or 2p orbital of He if partial charge exchange takes place when He meets a molecule. The effective RE will then be somewhat lower than 13.6 eV. 

In this equation Exc is the exchange correlation functional [46], is the partial charge of an atom in the classical region, Z, is the nuclear charge of an atom in the quantum region, is the distance between an electron and quantum atom q, r, is the distance between an electron and a classical atom c is the distance between two quantum nuclei, and r is the coordinate of a second electron. Once the Kohn-Sham equations have been solved, the various energy terms of the DF-MM method are evaluated as... 

The major problem in method (a) is that in ion-molecule interchange, considerable momentum in the direction of travel of the incident ion is imparted to both final products. Hence, in a perpendicular type apparatus only transfer of low weight particles can be observed at all and only at very low velocities of the incident ions (1, 9, 10, 11, 12, 13, 19, 20, 23, 27). Cross-sections cannot be measured. The value of these investigations is that some ion-molecule reactions—e.g., proton transfer and hydride ion transfer—can be identified. The energetics and the competition between charge exchange and ion-molecule reactions can be discussed, and by using partially deuterated compounds, one can obtain a detailed picture of the reaction. 

From the comparison of the results, it can be inferred that copper ions exchanged in the ZSM-5 zeolites assumes a bidentate (sites 12 and II) or tridentate coordination (sites M5, Z6, and M7). These two groups differ also in the molecular properties (Table 2.2). The I-centers are characterized by lower values of the valence index and greater partial charges, QCu, in comparison to the M and Z centers, which is associated with the deeper laying HOMO and LUMO levels. In the M5, Z6, and M7 sites Cu1 ions exhibit more covalent character, and the frontier orbitals have less negative energies. As a result, the chemical hardness of the I-centers, located at the channel intersections, is smaller than those located on the walls of the ZSM-5 zeolite. 

Dalgarno and Griffing (1958) made a detailed theoretical analysis of the ionization produced by a beam of protons penetrating a gas of H atoms. They find that the W value remains constant at around 36 eV, to within 2.5 eV, for proton energies of 10 KeV and up. However, below about 100 KeV, the near constancy of the W value is also partially due to the fact that the beam is a near equilibrium composition of protons and H atoms because of charge exchange. Therefore, at... 

Kinetic Acidities in the Condensed Phase. For very weak acids, it is not always possible to establish proton-transfer equilibria in solution because the carbanions are too basic to be stable in the solvent system or the rate of establishing the equilibrium is too slow. In these cases, workers have turned to kinetic methods that rely on the assumption of a Brpnsted correlation between the rate of proton transfer and the acidity of the hydrocarbon. In other words, log k for isotope exchange is linearly related to the pK of the hydrocarbon (Eq. 13). The a value takes into account the fact that factors that stabilize a carbanion generally are only partially realized at the transition state for proton transfer (there is only partial charge development at that point) so the rate is less sensitive to structural effects than the pAT. As a result, a values are expected to be between zero and one. Once the correlation in Eq. 13 is established for species of known pK, the relationship can be used with kinetic data to extrapolate to values for species of unknown pAT. 

The effect of temperature on the relative molecular ion abundances in the mass spectra of CH4 and CD4 has been studied [493]. Isotope effects have been determined in the charge exchange mass spectra of partially deuterated methanes [682]. 

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