6533b853fe1ef96bd12ad3b6

RESEARCH PRODUCT

Singlet and triplet potentials of the ground-state atom pair Rb+Cs studied by Fourier-transform spectroscopy

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A comprehensive study of the $X {}^{1}\ensuremath{\Sigma}{}^{+}$ and $a {}^{3}\ensuremath{\Sigma}{}^{+}$ electronic states of the Rb and Cs atom pair in RbCs is presented. Abundant spectroscopic data for the $^{85}\mathrm{Rb}$$^{133}\mathrm{Cs}$ and $^{87}\mathrm{Rb}$$^{133}\mathrm{Cs}$ isotopologues were obtained from Fourier-transform spectra of laser-induced fluorescence (LIF) from the $B {}^{1}\ensuremath{\Pi}$ and $(4){}^{1}\ensuremath{\Sigma}{}^{+}$ states to the $a {}^{3}\ensuremath{\Sigma}{}^{+}$ (4549 transitions) and $X {}^{1}\ensuremath{\Sigma}{}^{+}$ (15 709 transitions) states. The $X {}^{1}\ensuremath{\Sigma}{}^{+}$ state data were complemented by about 15 500 transitions obtained by Fellows et al. [J. Mol. Spectrosc. 197, 19 (1999)]. LIF progressions to the $a {}^{3}\ensuremath{\Sigma}{}^{+}$ state range from ${v}_{a}=0$ to 37, reaching an outer turning point at 15.97 \AA{}. For the $X {}^{1}\ensuremath{\Sigma}{}^{+}$ state, by analyzing LIF from the shelflike $(4){}^{1}\ensuremath{\Sigma}{}^{+}$, the data are extended from ${v}_{x}=119$ as observed in the above-cited paper to ${v}_{x}=129$, extending the outer turning point from 10.7 to 17.55 \AA{}. From these data, potential energy curves were constructed simultaneously for both hyperfine coupled states $X {}^{1}\ensuremath{\Sigma}{}^{+}$ and $a {}^{3}\ensuremath{\Sigma}{}^{+}$ in a coupled-channels fitting routine. This allowed us to accurately model the potential close to the Rb(5$s$) $+$ Cs(6$s$) atom-pair asymptote, which is required to simulate cold collision processes and to analyze the Feshbach resonances observed for $^{87}\mathrm{Rb}$$^{133}\mathrm{Cs}$ by Pilch et al. [Phys. Rev. A 79, 042718 (2009)]. Dissociation energies were determined for the $X {}^{1}\ensuremath{\Sigma}{}^{+}$ state as ${D}_{e}=3836.373(40)$ cm${}^{\ensuremath{-}1}$ and for the $a {}^{3}\ensuremath{\Sigma}{}^{+}$ state as ${D}_{e}=259.341(30)$ cm${}^{\ensuremath{-}1}$.