Additionally, since H2 has a lower ionization energy and a stronger interatomic strength compared to CO , the ionization and fragmentation of H2 are less influenced by the applied EI energy. Thus, the compositions of [H2]+ and H+ ions are less influenced than those of CO molecules. Taken together, the possibility of CO colliding with [H2]+ or H+ is reduced at 28 eV. In the case of Ar, it is a monoatomic molecule and is also inert, fragmentation does not happen and its ionization is also less influenced by EI energy. Therefore, the possibility of Chem-I between Ar and [H2]+ or H+ is less influenced and thus occurs at both 28 eV and 70 eV.