Knowledge Bank

The $A1\Sigma u+$ and $ b,^3\Pi_{0u}$ states of the rubidium dimer has been re-investigated experimentally, adding to the considerable array of upper state term values determined from earlier work (performed at Laboratoire Aime Cotton to characterize the electronic ground state). A polarization labelling experiment probed a series of levels from $v$=0, $J$=71 in the $X1\Sigma g+$ state, and $(A1\Sigma u+\sim b3\Pi 0u)\to X1\Sigma g+$ fluorescence spectra have been recorded on an FT spectrometer following excitation of low-lying vibrational levels in the $A$ state by a Ti:sapphire laser operating with long wavelength optics. Data for $\mathrm{<mrow\; data-mjx-texclass="ORD">85</mrow>}$Rb$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$, $\mathrm{<mrow\; data-mjx-texclass="ORD">85</mrow>}$Rb$\mathrm{<mrow\; data-mjx-texclass="ORD">87</mrow>}$Rb and $\mathrm{<mrow\; data-mjx-texclass="ORD">87</mrow>}$Rb$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$ are modeled using the discrete variable representation, fitting to numerical potential curves and Morse-type spin-orbit functions starting from \emph{ab initio} potentials and spin-orbit functions. The fit has confirmed absolute vibrational numbering in the $A$ state (the vibrational assignment in the $b$ state looks convincing but is not definitive). The fit currently returns a root mean square residual of 0.075 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$, which is 15 $\times$ the estimated experimental uncertainty, reflecting the fact that information particularly on the $b$ state is still sparse. Including the $ b,^3\Pi_{1}$ component in the Hamiltonian did not improve the fit. Nevertheless, the fit provides useful estimates of term values and of spin-orbit mixing effects.\newline Work at Stony Brook was supported by NSF grant PHY 0652459 and at Temple University by NSF PHY 0555608.