We report a combined experimental and theoretical study of the structures and ionization potentials of small InNO clusters (N=1-8). The clusters are produced using a laser vaporization cluster source, laser ionized, and mass selectively recorded by a time-of-flight mass spectrometer. Threshold photoionization spectroscopy was performed using photon energies of 4.59-5.96 eV and 6.43 eV. Adiabatic and vertical ionization potentials were compiled from the photoionization efficiency curves. Remarkably low values were obtained for In3O and In7O. Geometric and electronic structures of the InNO and InNO+ clusters were computed with density functional theory using the hybrid B3LYP functional. The bonding in these clusters is analyzed by means of Bader's atoms in molecules method. Calculated adiabatic and vertical ionization potentials are in good agreement with the experimental values. (C) 2003 American Institute of Physics.