Diatomic AlCu has been interrogated using resonant two-photon-ionizati
on spectroscopy in a supersonic expansion of helium. The ground state
is shown to be X 1SIGMA+, deriving from the 3s(Al)(2)3d(Cu)10sigma2 co
nfiguration, in agreement with theoretical predictions. The closed-she
ll nature of this molecule results in a low density of electronic stat
es, allowing the chemical bonding and electronic structure to be inves
tigated in detail. Five excited electronic states have been observed a
nd characterized, leading to a potential energy diagram based solely o
n experimental results. Constants experimentally determined for AlCu i
nclude a ground state bond length (r0) of 2.3389+/-0.0004 angstrom, a
dissociation energy, D0-degrees, of 2.315+/-0.012 eV, and an ionizatio
n potential of 7.065+/-0.014 eV.