Missing bands in the multiphoton excitation of coupled molecular states

Measurements are reported of (3+1) resonance-enhanced multiphoton ionization of O₂via the F³Π_ustate which show near-vanishing intensity for F-X(1,0), the strongest band in one-photon spectra. Using a coupled-channel treatment of the³Π_uRydberg-valence interactions, this dramatic result is attributed to destructive interference between the amplitudes for transitions into the Rydberg and valence components of the heavily mixed F state, indicating a significant dependence of the relative transition amplitudes on the mode of excitation. Thus, “missing bands” in the multiphoton spectra of coupled states provide important information on relative multiphoton transition probabilities.