The states 1^1\Sigma^+_u, 1^1\Pi_u and 2^1\Sigma^+_u of Sr_2 studied by   Fourier-transform spectroscopy
  A high resolution study of the electronic states 1^1\Sigma^+_u and 1^1\Pi_u which belong to the asymptote 4^1D + 5^1S and of the state 2(A)^1\Sigma^+_u, which correlates to the asymptote 5^1P + 5^1S, is performed by Fourier-transform spectroscopy of fluorescence progressions induced by single frequency laser excitation. Precise descriptions of the potentials up to 2000 cm^{-1} above the bottom are derived and compared to currently available ab initio calculations. Especially for the state 1^1\Sigma^+_u large deviations are found. Rather weak and local perturbations are observed for the states 1^1\Pi_u and 2^1\Sigma^+_u, while a strong coupling of the state 1^1\Sigma^+_u to the component \Omega=0^+_u of the state 1^3\Pi_u, which belongs to the asymptote 5^3P + 5^1S, is indicated. 
Alexander Stein, Horst Kn\"ockel, Eberhard Tiemann
physics.chem-ph