Collisional detachment

Collisional Detachment. Reactions of negative ions in flames not containing hydrocarbons have not been widely studied, although OH -ion formation is important in flames containing high electron concentrations. The rate constant k l of the reaction... 

Fig. 2. Laser photodetachment-reionization of CH2N02 plotted as a difference of laser-on and laser-off measurements. The upward peaks are due to dissociations upon photodetachment followed by reionization with 02 and cation detection. The downward peaks are due to dissociations upon collisional detachment due to residual 02 followed by reionization with 02...

Electrons can be released from negative ions, either by photodetachment or by collisional detachment ... 

Abbreviations used in the tables calc = calculated value PT = photodetachment threshold using a lamp as a light source LPT = laser photodetachment threshold LPES = laser photoelectron spectroscopy DA = dissociative attachment attach = electron at-tachment/detachment equilibrium e-scat = electron scattering kinetic = dissociation kinetics Knud=Knudsen cell CT = charge transfer CD = collisional detachment and ZEKE = zero electron kinetic energy spectroscopy. 

Reactions which are the reverse of those mentioned here as preparative techniques are important negative-ion loss processes under some conditions. Associative detachment, collisional detachment, ion-ion recombination, and photodetachment are the reverse processes to those discussed in Sections 2.1-2.4. Several reviews of these subjects are available. ... 

Bailey and Mahadevan have used a radiofrequency filter to measure separately the currents of electrons and of slow negative ions resulting from collisions between O2 and several negative ion species (H", O , OH , 02 ) in the range of reactant ion energies from about 8 to 350 eV. In the case of H 4- O2, the slow product ions are principally O2" from reaction (9), and the cross section shows a maximum of 13 x 10" cm at 8 eV decreasing to 6 x 10 cm at 350 eV. The electron currents observed by Bailey and Mahadevan in reaction of H with O2 were ascribed entirely to collisional detachment... 

Several reported negative-ion-neutral reactions have not been discussed in this chapter. Included in this group are many associative detachment, collisional detachment, and collisional dissociation reactions. 

The statistical time lag 4 can vary from nanoseconds to milliseconds (or longer) depending on the time the initiatory electron becomes available when V > Vs. Initiatory electrons can be produced by cosmic radiation, natural radioactivity from materials, field emission from the cathode surface, or collisional detachment from negative ions in the case of electronegative gases. In experimental apparatus they can be produced intentionally by, for instance, an ultraviolet source, in which case ts is reduced considerably. 

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