Ground-state potential of the Ca dimer from Fourier-transform spectroscopy

The $B{}^{1}{\ensuremath{\Sigma}}_{\mathrm{u}}^{+}\ensuremath{\rightarrow}X{}^{1}{\ensuremath{\Sigma}}_{\mathrm{g}}^{+}$ system in ${}^{40}{\mathrm{Ca}}_{2}$ was studied by Fourier-transform spectroscopy. Transitions to 730 ground-state levels were induced by the blue-green lines of an ${\mathrm{Ar}}^{+}$ radiation and the single-mode radiation of a frequency-doubled continuous-wave Nd:YAG yttrium aluminum garnet laser. An accurate potential-energy curve, which covers 99.8% of the well depth, was derived directly from the experimentally observed differences between ground-state levels. Long-range analysis led to a revised value of the ground-state dissociation energy, $1102.08(9){\mathrm{cm}}^{\ensuremath{-}1},$ which differs by more than $7{\mathrm{cm}}^{\ensuremath{-}1}$ from the previous experimental determination [C. R. Vidal, J. Chem. Phys. 72, 1864 (1980)]. A first estimate of the s-wave scattering length is reported.