Electron attachment radiative

In divertor regions with temperatures below a few eV, II ions may be formed by radiative electron attachment... 

The product 0 is LaPorte-forbidden to decay radiatively to the P° state. This metastable P° state of 0 would be expected to have a rather long lifetime. Electron attachment to the excited P° state may then yield the triplet 2p 3p 3p[l/2]o state of 0 . 

Thermal electron attachment studies in our laboratory utilize the so-called electron capture detector which is commonly used as a selective detector for gas chromatography. Our measurements are also carried out in conjunction with a gas chromatograph for reasons pointed out later. The electronic circuitry for the pulse mode of operation is identical to that originally proposed by Lovelock et al. (14,15). The electron capture cell, employing tritium as a radiative /3-source, has been modified slightly for practical reasons (22) however, the basic electrode geometry is parallel plate, as first proposed (14, 15). 

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. 

In some cases, long-wavelength emissions in electroluminescence occur that are not observed in the photoluminescence spectra. These long-wavelength emissions are postulated to arise from electromers and electroplexes, respectively. The mechanism of the latter type of emission is by phosphorescence or by direct radiative recombination of holes and electrons attached at two neighboring molecules [82]. The terms electromers and electroplexes are complete analogies to excimers and exciplexes. 

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.. 

Winnik [49] used fluorescence measurements of transfer of the electronic excitation between donor-naphthalene and acceptor-pyrene chromophores attached to the same polymer chain for studies of thermoreversible phase separation of aqueous solutions of poly(N-isopropylacrylamide) (PNIPAM). Dilute solutions of the doubly labelled polymer PNIPAM were heated from 277 K to 313 K, and the fluorescence emission intensity of pyrene (integrated spectrum) was measured when the system was excited with 290 nm, donor excitation, and when excited with 328 nm, acceptor excitation. Non radiative energy transfer between excited naphthalene and pyrene occurred in aqueous solution of the polymer. The increase in intensity of pyrene fluorescence when the solution was excited at 290 nm, shown in Figure 4.13, is due to a phase separation process at lower critical solution temperature (LCST). When the LCST was reached, the phase separation into polymer-rich and polymer-lean phases occurred. It was concluded that the collapse of the polymer chain leading to densification of polymer phase is followed by domination of intramolecular contributions to the energy transfer process. 

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... 

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