Double-minimum potential-energy curves resulting from adiabatic effects: The 4s 3Σg+ state of the hydrogen molecule

Born-Oppenheimer potential-energy curve and adiabatic corrections for the 4s 3Σg+ state of the hydrogen molecule have been computed using an explicitly correlated wave function in elliptic coordinates. It is shown that, in contrast to the Born-Oppenheimer results, the adiabatic potential-energy curve for this state is characterized by a double-minimum function. The energies of the vibrational levels and rotational constants have also been computed. Large and irregular differences have been found between thoeretical and experimental results