High-angular-momentum states as population traps in multiphoton ionization

Resonant and nonresonant multiphoton ionization of xenon is studied using short, circularly polarized light pulses (100 fs, 597 nm, 22 TW/${\mathrm{cm}}^2$). A pump-probe measurement shows that, although bound states are substantially populated, they do not enhance the ionization signal. The bound states do not ionize because their high angular momentum repels the wave functions from the nucleus. Ionization does occur through intermediate states in the continuum, in spite of a large energy mismatch, because these states have more energy and therefore suffer less from the centrifugal barrier.