Ion neutralization

In radiolysis, a significant proportion of excited states is produced by ion neutralization. Generally speaking, much more is known about the kinetics of the process than about the nature of the excited states produced. In inert gases at pressures of a few torr or more, the positive ion X+ converts to the diatomic ion X2+ very rapidly. On neutralization, dissociation occurs with production of X. Apparently there is no repulsive He2 state crossing the He2+ potential curve near the minimum. Thus, without He2+ in a vibrationally excited state, dissociative neutralization does not occur instead, neutralization is accompanied by a col-lisional radiative process. Luminescences from both He and He2 are known to occur via such a mechanism (Brocklehurst, 1968). 

In alkanes, excited states are mainly produced by ion neutralization where the triplet contribution dominates. 

In aromatics, both singlet and triplet excited states of the solvent are produced in comparable yields, with some contribution from direct excitation. 

Energy transfer to the solute is readily observed in aromatics. When observed in alkanes, it is mainly a singlet-singlet transfer. 

In alicyclic hydrocarbon solvents with aromatic solutes, energy transfer (vide infra) is unimportant and probably all excited solute states are formed on neutralization of solute cations with solute anions, which are formed in the first place by charge migration and scavenging in competition with electron solvent-cation recombination. The yields of naphthalene singlet and triplet excited states at 10 mM concentration solution are comparable and increase in the order cyclopentane, cyclohexane, cyclooctane, and decalin as solvents. Further, the yields of these 

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INS Ion neutralization An inert gas hitting surface is spectroscopy [147] neutralized with the ejection of an Auger electron from a surface atom Spectroscopy of Emitted Ions or Molecules Kinetics of surface reactions chemisorption... 

Ferguson E E 1972 Review of laboratory measurements of aeronomic ion-neutral reactions A/ / . Geophys. 28 389... 

Adams N G and Smith D 1976 The selected ion flow tube (SIFT) a technique for studying ion-neutral reactions Int J. Mass Spectrom. Ion Phys. 21 349... 

Smith D and Adams N G 1988 The selected ion flow tube (SIFT) studies of ion-neutral reactions Adv. At Mol. Phys. 24 1-49... 

Lindinger W and Smith D 1983 Influenoe of translational and internal energy on ion-neutral reaotions Reactions of Small Transient Species ed A Fonti]n and M A A Clyne (New York Aoademio)... 

Cordonnier M, Uy D, Dickson R M, Kew K E, Zhang Y and Oka T 2000 Selection rules for nuclear spin modifications in ion-neutral reactions involving Hg" J. Chem. Phys. 113 3181-93... 

Figure Bl.7.12. A schematic diagram of a typical selected-ion flow (SIFT) apparatus. (Smith D and Adams N G 1988 The selected ion flow tube (SIFT) studies of ion-neutral reactions Advances in Atomic and Molecular Physics vol 24, ed D Bates and B Bederson p 4. Copyright Academic Press, Inc. Reproduced with pennission.)...

The electrostatic interaction results from the interaction of tire ion with the pennanent multipole moments of the neutral. For cylindrically synnnetric neutrals or linear molecules, the ion-neutral multipole interaction is... 

Initial spray of analyte ions, neutrals and solvent molecules... 

A discharge ignited in argon and coupled inductively to an external high-frequency electromagnetic field produces a plasma of ions, neutrals, and electrons with a temperature of about 7000 to 10,000°C. Samples introduced into the plasma under these extremely energetic conditions are fragmented into atoms and ions of their constituent elements. These ions are examined by a mass analyzer, frequently a quadrupole instrument. 

The gas pressure in the first hexapole section is influenced by gas leaking in from the inlet system and, at about 10" mbar, is higher than desirable if excessive ion/neutral collisions are to be prevented. Therefore, the first hexapole is separated from the second hexapole section by a small orifice, which allows ions to pass through. 

Chaise-inversion reaction. An ion/neutral reaction wherein the charge on the reactant ion is reversed in sign. 

CoIIisional activation. An ion/neutral process wherein excitation of a (fast) projectile ion is brought about by the same mechanism as in collision-induced dissociation. (The ion may decompose subsequently). 

CoIIisional excitation. An ion/neutral process wherein the (slow) reactant ion s internal energy increases at the expense of the translational energy of either (or both) of the reacting species. The scattering angle can be large. 

Collision-induced dissociation (or decomposition), abbreviated CID. An ion/neutral process wherein the (fast) projectile ion is dissociated as a result of interaction with a target neutral species. This is brought about by conversion during the collision of part of the translational energy of the ion to internal energy in the ion. The term collisional-activated dissociation (or decomposition), abbreviated CAD, is also used. 

Elastic scattering. An ion/neutral interaction wherein the direction of motion of the ion is changed, but the total translational energy or internal energy of the collision partners remains the same. 

Ion energy loss spectrum. A spectrum that shows the loss of translation energy among ions involved in ion/neutral reactions. 

Ionizing collision. An ion/neutral reaction in which an electron or electrons are stripped from the ion and/or the neutral species in the collision. Generally, this term describes collisions of fast-moving ions or atoms with a neutral species in which the neutral species is ionized. Care should be taken to emphasize if charge stripping of the ion has taken place. 

Ion/neutral exchange reaction. An association reaction that subsequently or simultaneously liberates a different neutral species. 

Ion/neutral reaction. Interaction of a charged species with a neutral reactant to produce either chemically different species or changes in the internal energy of one or both of the reactants. 

Partial charge-transfer reaction. An ion/neutral reaction that reduces the charge on a multiply charged reaction ion. 

Translational spectroscopy. A technique to investigate the distribution of the velocities of product ions from ion/neutral reactions. 

HEED = high energy electron diffraction IILE = ion-induced light emission INS = ion-neutralization spectroscopy IRS = infrared spectroscopy ISS = ion-scattering spectroscopy LEED = low energy electron diffraction LEIS = low energy ion scattering ... 

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