Fourier-transform spectroscopy ofSr2and revised ground-state potential

Abstract

Precise potentials for the ground-state $X\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Sigma}_{g}^{+}$ and the minimum region of the excited state $2\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Sigma}_{u}^{+}$ of ${\mathrm{Sr}}_{2}$ are derived by high-resolution Fourier-transform spectroscopy of fluorescence progressions from single-frequency laser excitation of ${\mathrm{Sr}}_{2}$ produced in a heat pipe at $950\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. A change of the rotational assignment by four units compared to an earlier work [G. Gerber et al., J. Chem. Phys. 81, 1538 (1984)] is needed for a consistent description leading to a significant shift of the potentials toward longer interatomic distances. The huge amount of ground-state data derived for the three different isotopomers $^{88}\mathrm{Sr}_{2}$, $^{86}\mathrm{Sr}^{88}\mathrm{Sr}$, and $^{87}\mathrm{Sr}^{88}\mathrm{Sr}$ (almost 60% of all excisting bound rovibrational ground-state levels for the isotopomer $^{88}\mathrm{Sr}_{2}$) fixes this assignment beyond a doubt. The presented ground-state potential is derived from the observed transitions for the radial region from $4\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}11\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ ($9\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ below the asymptote) and is extended to the long-range region by the use of theoretical dispersion coefficients together with already available photoassociation data. New estimations of the scattering lengths for the complete set of isotopic combinations are derived by mass scaling with the derived potential. The data set for the excited state $2\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Sigma}_{u}^{+}$ was sufficient to derive a potential energy curve around the minimum.