Field ionization kinetics and metastable ions

With metastable ions, the isotope effect Ij/In is obtained from metastable ion abundances. The abundance is given by the area under the metastable peaks after the peak has been deconconvoluted to remove the broadening effect of finite slit widths and other factors. The usual procedures adopted in practice are either to work with narrow slits, determine peak areas and neglect deconvolution, or to work with wide slits and measure peak heights. 

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]). 

With FIK and metastable ions, the observation window, A t = t, — t2, is narrow (Sects. 3.2 and 3.3) and the range of internal energies, E, contributing significantly to the measured ion current may, therefore, be narrow. There is, therefore, some possibility that within the narrow energy range the kinetic isotope effect ki(E)/kn(E) will be constant, 

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