Multichannel quantum-defect theory of double-minimumΣg+1states inH2. II. Vibronic-energy levels

In the preceding paper [Phys. Rev. A 49, 3888 (1994)] we obtained the quantum-defect matrix of the strongly interacting double-minimum states of ${\mathrm{H}}_2$ by fitting to the ab initio clamped-nuclei electronic energies of Wolniewicz and Dressler [J. Chem. Phys. 82, 3292 (1985), and private communication]. Yu, Dressler, and Wolniewicz have calculated the vibronic energies of the corresponding states using an approach involving the state-by-state evaluation of vibronic coupling, and the solution of a set of coupled equations. Here we calculate the vibronic energies using our quantum-defect matrix in a version of scattering theory known as multichannel quantum-defect theory (MQDT). This less traditional treatment involves both singly and doubly excited channels and reproduces the vibronic energies to almost the same precision as the coupled-equations approach. In addition, several refinements have been made to MQDT.