Electronically excited states of Mg+(NH3) are studied by photodissociation after mass selection. The dissociation spectrum shows relatively sharp vibronic transitions centered at about 28 000 and 36 000 cm(-1). These absorption bands are assigned to the P-2-S-2 type transitions localized on the Mg+ ion. In photodissociation, a photoinduced charge-transfer process to produce NH3+ is observed in addition to evaporation and intracluster reaction processes to produce Mg+ and MgNH2+ ions, respectively. The mechanism for the production of these ions is discussed in terms of the predissociative and non-adiabatic interactions between the low-lying states. C0 2001 Elsevier Science BN. All rights reserved.