  We report on the formation of ultralong-range Rydberg D-state molecules via
photoassociation in an ultracold cloud of rubidium atoms. By applying a
magnetic offset field on the order of 10 G and high resolution spectroscopy, we
are able to resolve individual rovibrational molecular states. A full theory,
using the Born-Oppenheimer approximation including s- and p-wave scattering,
reproduces the measured binding energies. The calculated molecular
wavefunctions show that in the experiment we can selectively excite stationary
molecular states with an extraordinary degree of alignment or anti-alignment
with respect to the magnetic field axis.
