Additionally, we located the position of an optically dark autoionizing state of symmetry Σ 𝑔 + 1 that cannot be reached by a one-photon transition from the ground state and has a computed energy that is 15.8 eV above the ground state. To assess the extent to which this state could contribute to the FWM process, we then computed the oscillator strengths for transitions from this state to the bright Rydberg autoionizing states and the oscillator strengths from the ground state to the same bright states. These oscillator strengths were obtained using a purely bound state calculation, which was performed with the same MCSCI code that was used in the scattering calculations. In these calculations, we extended the aug-cc-pVTZ basis set used in the main scattering calculations with a set of Rydberg-like Gaussian basis functions of Kaufmann et al. as defined by Eq. ( ) of that paper. The added Gaussian functions had 𝑙 = 0 with 𝑛 = 1.5, 2.0, … , 6.0, 𝑙 = 1 with 𝑛 = 2.0, 2.5, … , 4.0, and 𝑙 = 2 with 𝑛 = 2.5,3.0, … ,7.0, where these 25 added functions all had 𝜎 symmetry.