We present a new mechanism contributing to the detection of photoassociated
long-range Rydberg molecules via pulsed-field ionization: ionic products,
created by the decay of a long-range Rydberg molecule, modify the excitation
spectrum of surrounding ground-state atoms and facilitate the excitation of
further atoms into Rydberg states by the photoassociation light. Such an
ion-mediated excitation mechanism has been previously called "Coulomb
anti-blockade". Pulsed-field ionisation typically doesn't discriminate between
the ionization of a long-range Rydberg molecule and an isolated Rydberg atom,
and thus the number of atomic ions detected by this mechanism is not
proportional to the number of long-range Rydberg molecules present in the probe
volume. By combining high-resolution UV and RF spectroscopy of a dense,
ultracold gas of cesium atoms, theoretical modeling of the molecular level
structures of long-range Rydberg molecules bound below nP_3/2 Rydberg states of
cesium, and a rate model of the photoassociation and decay processes, we
unambiguously identify the signatures of this detection mechanism in the
photoassociation of long-range Rydberg molecules bound below atomic asymptotes
with negative Stark shifts.Comment: 8 pages, 7 figure