Effect of positive-energy orbitals on the configuration-interaction calculation of theH−atom

We present the theoretical energy eigenvalues of the ${}_{}{}^1{}_{}{}^{}$S ground state and the (pp${)}^3$ ${\mathit{P}}^{\mathit{e}}$ state of ${\mathrm{H}}^{\mathrm{-}}$ calculated in a simple configuration-interaction procedure, using a finite set of ${\mathit{L}}^2$-basis functions constructed from one-electron hydrogenic orbitals. The energy corrections, due to the electron-electron interaction between configurations with various combinations of bound (negative-energy) and continuum (positive-energy) orbitals, are examined in detail. In particular, our calculation has shown that the continuum-continuum type of configurations contribute approximately 15% and 13%, respectively, to the electron affinity of the ${}_{}{}^1{}_{}{}^{}$S ground state and the (pp${)}^3$ ${\mathit{P}}^{\mathit{e}}$ state of ${\mathrm{H}}^{\mathrm{-}}$. In addition, our calculation has shown that the calculated oscillator strength for the transition from the ${}_{}{}^1{}_{}{}^{}$S ground state of ${\mathrm{H}}^{\mathrm{-}}$ to the lowest ${}_{}{}^1{}_{}{}^{}$P Feshbach resonance below the n=2 threshold is significantly reduced (nearly 30%) by the presence of the continuum-continuum type of configurations in the ground-state wave function.