Open shell ions

El predominantly creates singly charged ions from the precursor neutral. If the neutral was a molecule as in most cases, it started as having an even number of electrons, i.e., it was an even-electron (closed-shelT) molecule. The molecular ion formed must then be a radical cation or an odd-electron open-shell) ion as these species are termed, e.g., for methane we obtain ... 

Electron ionization mainly creates singly charged positive ions by ejection of one electron out of the neutral. If the precursor was a molecule, M, it will have an even number of electrons, i.e., an even-electron or closed-shell species. The molecular ion formed upon EI must then be a positive radical ion, M" , odd-electron or open-shell) ion. 

Mass and Electron Parities, Closed-Shell Ions and Open-Shell Ions 6.6.1 Electron Parity... 

The spectrum of ethyl benzoate (top) contains an ion of mass 122 Da. In the absence of nitrogen, it indicates an open-shell ion, or odd-electron ion. This is an application of the... 

A technique for treating excitations of an -electron atom, the so-called method of fractional parentage", was developed by Racah in the 1940 s (18). The details of the application of this method to the ionization of open shell ions is treated by Cox (7)... 

For a closed-shell ground-state molecule, those properties that involve only the ground-state wave function can be calculated just as well with either the localized of the delocalized MO description. Such properties include electron probability density, dipole moment, geometry, and heat of formation. Properties of a molecule that involve the wave function of the ground state and also the wave function of an open-shell excited state or the wave function of an open-shell ion cannot be calculated using a localized MO description. Such properties include the electronic absorption spectrum and molecular ionization energies. 

Our analysis will include only structures with an even number of electrons in the cyclic n system. For a discussion of the possibility of aromaticity in open shell, ion-radical cyclic n systems, see Rosokha, S. V. Kochi, J. K. /. Org. Chem. 2006, 71, 9357. 

Clary DC, Dateo CE, Smith D. (1990) Rates for the reactions of open-shell ions with molecules. Chem. Phys. Lett. 167 1-6. 

An additional advantage of this arrangement is the possibility of tracing hot-band transitions not only for open-shell ions but also for free radicals. 

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