Excited states of the hydrogen molecule in magnetic fields: The singlet $\Sigma$ states of the parallel configuration

Excited states of the hydrogen molecule that are subject to a homogeneous magnetic field are investigated for the parallel configuration in the complete regime of field strengths $B=0\mathrm{}–100\hspace{0.5em}\mathrm{a}.\mathrm{u}.\mathrm{}$ Up to seven excitations are studied for gerade as well as ungerade spin singlet states of $\Sigma$ symmetry with a high accuracy. The evolution of the potential-energy curves for the individual states with increasing field strength, as well as the overall behavior of the spectrum, are discussed in detail. A variety of phenomena such as the sequence of changes for the dissociation channels of excited states and the resulting formation of outer wells are encountered. Possible applications of the obtained data to the analysis of magnetic white dwarfs are outlined.