Special case of negative ions

The field of application of the metastable decompositions (whether collision-induced or not) of positive ions is very important. Nevertheless, Hunt and Sethi [51] showed the value of studying the behavior of negative ions they very often provide complementary ion structural data, with a better sensitivity. 

Bowie and Hart [159] used the IKE technique to study the decomposition of negative molecular ions M (produced by electron capture) into fragment ions according to mechanisms of simple rupture and of rearrangements. 

The following compounds o-nitroacetanilide and phenyl-(p-nitrophenyl) acetate lead to the elimination of radicals, such as (a) NOj (and also NHCOCH3 for acetanilide) directly from the initial negative molecular ion (b) NO, OH, (NO -f CH2CO) after molecular ion isomerization. Under collision conditions in the FFR, direct cleavages occur without isomerization of the molecular ion and lead to the formation of [M-NO2] , [M-O-Ph] and [M-PhCOO] ions. 

Measurements are performed with a conventional geometry instrument and the reactions occurred in the first FFR (unimolecular or collisional-induced decompositions). The value of the transitions is determined by measuring the E/Eq ratio, which yields nii/mi (m and m2 unknown) each term can be determined as soon as the ion beam which emerges from (— E) leaves the magnetic field at the value m2/mi. Thus, Wj and m2 can be calculated. 

Other types of reactions have been studied in collisional conditions, especially charge-inversion reactions. 

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