A new molecular electronic band system has been observed in the near UV by laser fluorescence excitation in a free-jet supersonic expansion of photolyzed Fe(CO)(5) diluted in seed gases containing acetonitrile. The three observed bands displayed the rotational structure of a Omega'=7/2 <--Omega"=9/2 transition and could be assigned as an excited-state progression in a single vibrational mode. The rotational constant B" and its change upon isotopic substitution in acetonitrile [(CH3CN)-C-13] was consistent with the assignment of the molecular carrier as the linear FeNC molecule. In analogy with the iron monohalides, which have electronic band systems in the same wavelength range, the transition can be described as a 4p <-- 4s excitation. The derived structure is compared with that of other metal-containing cyanide/isocyanide molecules. (C) 2001 American Institute of Physics.