SPIN-ORBIT MIXING IN THE A\,^1\Sigma^+_u AND b\,^3\Pi_{0u} STATES OF THE RUBIDIUM DIMER

Abstract

Author Institution: Universite Lyon 1 and CNRS (LASIM, UMR 5579), 69622 Villeurbanne, France; Department of Physics and Astronomy, SUNY; Stony Brook, NY 11794-3800; Laboratoire Aime Cotton, CNRS, Bat. 505, Campus d'Orsay, 91405; Orsay, France; Physikalisch-Technische Bundesanstalt, Braunschweig, Germany; Department of Physics, Temple University, Philadelphia, PA 19122-6082The A\,^{1}\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 X\,^{1}\Sigma_g^{+} state, and (A\,^{1}\Sigma_u^{+}\sim b\,^3\Pi_{0u})\,\rightarrow\,X\,^{1}\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 $^{85}$Rb$_{2}$, $^{85}$Rb$^{87}$Rb and $^{87}$Rb$_{2}$ 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$^{-1}$, 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