- Ion-molecule reactions of excited- and ground-state Fe+ with NO are reported. The charge-exchange and clustering ion-molecule reactions of Fe+ with Fe(CO)5 are used to study the reaction dynamics of metastable versus ground electronic state Fe+ ions. The ground-state 6D(4s13d6) Fe+ ions are unreactive with NO. Conversely, the metastable electronic states react with NO to form charge-transfer product ions (NO+) and radiative association adduct ions [Fe+(NO)] and by the collisional relaxation process. The collisional relaxation process gives rise to the ground-state 6D(4s13d6) and excited-state 6S(4s23d5) Fe+ ions. The 6S(4s23d5) Fe+ ion is unreactive with NO and constitutes approximately 6% of the Fe+ ion population. Molecular orbital concepts are used to explain the lack of reactivity for the 6S(4s23d5) Fe+ ions and also the collisional relaxation process by the high-lying 4s13d6 states to form the 6S(4s23d5) Fe+ ions. 1993, American Chemical Society. All rights reserved.