Field ionization kinetics FIK

The field ionization kinetics (FIK) technique allows rates of ionic decompositions to be determined over a continuous range of time extending from picoseconds to microseconds [38, 41, 223]. The applications of the technique have been reviewed [45, 226, 745]. 

The FIK experiment is essentially translational spectroscopy. The reactant ion M+ is formed, preferably in free space, at a potential V0 and decomposes in a strong electric field [41, 223], If the potential at the point of decomposition is, the translational energy of a product ion m+ on reaching a region at ground potential is 

The ion currents, 7ml, (numbers of ions per time) measured represent fragment ions formed within an observation window, whose limits depend upon the resolution in the measurement of translational energy [28]. It is arranged for these limits to be sufficiently close to each other so that the measured ion current, Iml, divided by the observation window (At = t2—t1) is proportional to the rate of decomposition dlVml/dt at that time (see Sect. 2.5). 

If energy is measured at a resolution of 1 in 100, times of the order of 10 ps are accessible and the observation windows are also of the order of 10ps (although time resolution does depend on M and m). Times of the order of picoseconds can be determined if higher energy resolution is obtained (1 in 103) and the ionization process is sufficiently well controlled [223]. 

The rates of decomposition [d/ml/dt = Gml(dNml/df)] obtained in FIK for molecular ions are generally normalized to give a normalized rate fej ( ) (phenomenological rate coefficient in some earlier papers) [43], This procedure assumes that the collection efficiency, G, is the same for all fragment ions and the stable molecular ions, viz. 

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In field ionization kinetics (FIK), the isotope effects (dli/dt)/(dlu/dt) are obtained from the rates at anytime. The following discussion applies equally to these isotope effects since the rates have been determined by measuring the ion abundances / formed within a time interval At (rate = IIAt [223]). 

Early El studies by King suggested that 1,3-butadiene radical cations suffer isomerization and complete hydrogen scrambling prior to loss of H and C2H2. Later, Gross, Nibbering and coworkers- -" showed by field ionization kinetic (FIK) measurements that... 

Field Ionization Kinetics (FIK) Although limited to select research laboratories, FIK can also reveal the mechanism of ion dissociation [45], This technique studies ions with lifetimes in the range 10 to 10 s. Ions are generated under the influence of very high potential by field ionization (see Section 2.6). The data are used to obtain the relation of the rate constant function k t) to the reaction time f. In combination with isotope labeling, FIK has been successful in identifying the fragmentation mechanism of a variety of gas-phase ions. 

Under field ionization kinetic conditions (FIK) the process of CH3 elimination from ionized 27 is not observed at t < 10-10 sec. This is a surprising result bearing in... 

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