Knowledge Bank

Atomic orbital 3d and 4s ionization energies and the 4p orbital exponent are assigned using gas phase UV Ni atom spectra. These parameters are used in a molecular orbital theory, producing an accurate description of the three observed electronic transitions in $Ni2$ and the two observed transitions in $Ni3$, and showing that the latter has a linear geometry. It is found that HOMO-LUMO transitions are not necessarily the strongest in intensity. It is suggested that antibonding interactions with the Ar matrix are responsible for the Ni atom frequency shifts.