  An oscillating electric field at 1.356 GHz was used to promote the resonant
energy transfer process: $43d_{5/2}+43d_{5/2} \to 45p_{3/2}+41f$ between
translationally cold $^{85}$Rb Rydberg atoms. The ac Stark shifts due to this
dressing field created degeneracies between the initial and final two-atom
states of this process. The ac field strength was scanned to collect spectra
which are analogous to dc electric-field-induced resonant energy transfer
spectra. Different resonances were observed for different magnetic sublevels
involved in the process. Compared to earlier work performed at higher
frequencies, the choice of dressing frequency and structure of the spectra may
be intuitively understood, by analogy with the dc field case.
