Thermodynamics of ammonia activation by iron cluster cations: guided ion beam studies of the reactions of Fen+ (n=2-10,14) with ND3

The kinetic energy dependences of the reactions of Fen 1 (n52 - 10,14) with ND3 are studied in a guided ion beam tandem mass spectrometer over the energy range of 0-10 eV. Dehydrogenation of ammonia to form FenND1 is found to be efficient and exothermic for n54 in agreement with previous FT-ICR studies. In contrast to the ICR studies, we also observe exothermic dehydrogenation for n=3 and 5, although these processes are much less efficient than for n=4. Other clusters also undergo this process but exhibit an energy threshold.