Radiative attachment

To stabilize the formation of a negative ion during electron attachment, the excessive energy canbe in principal emitted. As a result, the negative ion canbe formed in the process of radiative attachment ... 

Negative ions for use as reactants in ion-neutral reactions are usually prepared by dissociative electron attachment, three-body attachment, or ion-pair production. Other techniques available include radiative attachment and surface reactions. Finally, some negative ions can be formed most efficiently by ion-neutral reactions themselves. The following discussion of these processes is intended only to be illustrative, and references are made principally to review articles. 

It has been proposed from time-to-time, that negative ions are present in interstellar clouds in sufficient concentrations to allow significant fractions of the ambient positive ions to be neutralized by these negative ions (Dalgarno and McCray 1973, Herbst 1981). This is the process of mutual neutralization which is often termed binary ionic recombination. The important question has always been whether negative ions can form efficiently in interstellar clouds in binary collisions between electrons and attaching neutral species (i.e. by radiative attachment). This process has t>een considered for the formation of H ions in dense interstellar clouds and found to be very slow otherwise it would have initiated a gas phase route to H2 production when coupled with... 

Many years ago, one of us suggested that negative molecular ions could be formed in space via the process of radiative attachment. The simplest treatment of this process is to assume that it proceeds via a collision complex ... 

Even more so than for the case of radiative association, very little experimental information exists for radiative attachment, and the reliability of the simple phase-space treatment has not been tested. One possible problem is that the formation of the negative ion complex may require so-called doorway states known as dipole-bound states, in a similar manner to the Rydberg mechanism for dissociative recombination of positive molecular ions. Such states have been seen in the spectra of negative ions, although a detailed calculation employing them for radiative attachment has not been attempted. 

Radiative attachment is not the only mechanism for the production of anions their production in laboratory discharges probably occurs via dissociative attachment, in which electrons attach themselves to neutrals while a chemical bond is broken viz.. 

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