Dissociative Penning ionization

Metastable atom bombardment (MAB) is another suitable ionization option for gas-phase organic compounds [11,12]. In this approach, ionization occurs through Penning processes of the type shown in reactions (2.21) and (2.22) by bombarding the sample with a beam of metastable species. The process depicted in reaction (2.21) involves an electrophilic reaction of the metastable atom (A ) to produce an odd-electron molecular ion of the analyte. The excitation energy of A must exceed the IE of the analyte molecule. With much higher excitation energy, dissociative ionization process also takes place [reaction (2.22)]. 

Because of their high internal electronic energy (see Table 1), many decay channels are available in collisions of electronically excited inert gas atoms with other species [102,103]. These include various nonreactive pathways such as ionization (Penning, associative, and dissociative), excitation transfer, dissociative excitation, as well as a "chemical" deactivation channel, namely excimer formation. 

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