Multiphoton ionization of metal cluster complexes Os3(CO)12 and Ir4(CO)12: Determination of the ionization energy and coordination energy of the complex ions

Multiphoton ionization and the subsequent dissociation process of metal cluster complexes Os3(CO)12 and Ir4(CO)12, prepared in a supersonic jet, were studied by means of multiphoton ionization with time-of-flight (TOF) mass detection. The ionization energies of Os3(CO)12 and Ir4(CO)12 were determined to be 7.95 and 8.3 eV, respectively, from the laser wavelength at the ionization threshold. The coordination energies of Os3(CO)12+ and Ir4(CO)12+ ions were also determined to be 1.6 and 1.2 eV, respectively, from the excitation energy needed to cause the appearance of fragment ions. The observed values agreed reasonably well with the ones calculated by using the density functional theory method.