DOUBLY-EXCITED STATES IN THE SPECTRUM OF MOLECULAR-HYDROGEN

An ab initio calculation of the fixed-nuclei scattering information required for multichannel quantum defect applications is presented for several symmetries of molecular hydrogen. This represents a modest step toward the longer-range goal of constructing a unified theoretical description of all fragmentation channels in H-2, including ionization and both neutral and ionic dissociation channels. The errors in our calculated fixed-nuclei quantum defects are generally in the range 0.005-0.05. This is sufficiently accurate to consider a fully ab initio calculation of H-2 photoabsorption near the ionization threshold, including rovibrational channel interactions by the usual frame transformation method.