Reliability of estimation of recombination energies of molecular radical cations by charge exchange and a test of the exoergicity rule.

Charge exchange occurring in a collision cell of a mass spectrometer was used previously to find the very long-lived excited electronic states of molecular cations generated by electron ionization. The underlying criterion in the method, called the exoergicity rule, was that only electronically exoergic and resonant processes have large cross sections at low collision energy. The validity of this rule has been checked in this work by estimating the recombination energies of some molecular ions based on the presence/absence of charge-exchange signals from gases with different ionization energies, and comparing these estimates with the literature values. It is concluded that a recombination energy can be estimated to within an upper limit uncertainty of 0.1 eV with this technique, which validates the exoergicity rule proposed previously. Copyright 2003 John Wiley & Sons, Ltd.