To confirm this hypothesis, Fig. overlaps the HHG spectrum computed at the TDHF level with an excitation spectrum computed using linear response (LR) TDDFT. (We use LR-TDHF and thus compare to the TDHF data from Fig. . For clarity, only the LR-TDHF states with oscillator strengths greater than 1 × 10 -10 are shown.) It is apparent that the enhanced high-harmonic intensity around the 45th and 60th harmonic orders coincides with LR-TDDFT excitation energies having nonzero oscillator strengths. Thus, we conclude that these are enhancements in the high-harmonic spectrum driven by resonances with excited states of the system, but are not physically reasonable because the excited states in question lie well above the ionization threshold and are thus bound only by the finite support of the Gaussian basis set that prevents the molecule from ionizing. Note that the LR-TDDFT calculation exhibits resonances coinciding already with the 4th harmonic in the HHG spectrum and these may also be responsible for the lack of resolution that is observed in the TDKS simulations in Fig , even at lower harmonic orders.