(a) Total oscillating cross section of H⁻ ion in the harmonic potential plus the oscillating electric field, at electric field strength , the photon energy , and frequency in the harmonic potential and the oscillating electric field a.u. (b)–(h) Oscillating cross sections caused by the up orbit, down orbit, up–down orbit, down–up orbit, up–down–up orbit, down–up–down orbit, and the up–down–up–down orbit, respectively.