Collisional electron detachment

Less is known about Franck-Condon effects on collisional electron detachment from anions. For example, the C-N bond in CH2N02 (1.401 A) is 4.5% longer than the same bond in the CH2N02 anion (1.340 A), and vertical neutralization results in 25-30 kj mol-1 vibrational excitation in the radical, as calculated at several levels of theory [18]. Alkoxy radicals and anions also show different C-0 bond lengths, e.g., 1.317 A and 1.371 A in the 1-pentoxy anion and radical, respectively [1], although the Franck-Condon energies associated with... 

CgH (n = 6, 7, 8). A novel collision-induced isomerization of CgH7 (10a), which has a sttained allenic bond, to (lOyS) has been reported to occur upon SIFT injection of (10a) at elevated kinetic energies (KE) and collision with helium. In contrast, radical anions (9) and (11) undergo electron detachment upon collisional excitation with helium. Bimolecular reactions of the ions with NO, NO2, SO2, COS, CS2, and O2 have been examined. The remarkable formation of CN on reaction of (11) with NO has been attributed to cycloaddition of NO to the triple bond followed by eliminative rearrangement. 

In the studies outlined below, collisionally activated dissociation (MS/MS) experiments were attempted as a means of helping establish the identities of a number of anions. In every case tried, however, the parent anions appeared to undergo electron detachment with no daughter ion production observed. 

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... 

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. 

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... 

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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