Observation of the $^{85}$Rb$_{2}$ a $^{3}\Sigma _{u}^{+}$ State by PFOODR Resolved Fluorescence Spectroscopy*

Perturbation Facilitated Optical Optical Double Resonance (PFOODR) resolved fluorescence from a single rovibronic level of an excited triplet state ($^{3}\Pi _{g }$ or $^{3}\Sigma _{g}^{+}$) was used to characterize the a $^{3}\Sigma _{u}^{+}$ ground triplet state of $^{85}$Rb$_{2}$. A thermal Rubidium heatpipe source was used with a Titanium Sapphire pump laser and with a Toptika DL100 diode laser as the probe. The two color excitation was performed using an intermediate level with mixed singlet-triplet character belonging to the $A \quad ^{1}\Sigma _{u}^{+}\sim \quad b \quad ^{3}\Pi _{u}$ system. We have recorded resolved fluorescence from the PFOODR upper level to the a $^{3}\Sigma _{u}^{+}$ state using a combination of a SPEX 1404 double monochromator (resolution $\sim $0.2cm$^{-1})$ and a DA8 BOMEM FTIR (resolution $\sim $0.015cm$^{-1})$ interferometer. The multi-parameter Morse Long Range potential method was used to analyze the observed bound-bound and bound-free components of the spectra to construct the $a^{3}\Sigma _{u}^{+}$ potential curve.