ELECTRIC-FIELD EFFECTS IN THE PHOTOIONIZATION OF N2 NEAR THRESHOLD

Structural features well below the usual Stark field depression of the ionization threshold are observed in the photoionization of N2 in the presence of weak (10-15 V/cm) fields. The energies of the structural features can be simulated by assuming rotational autoionization (ΔJ = -2). They are interpreted as originating from Q (J″) transitions, forbidden to spontaneously autoionize in the absence of a field. The field relaxes the rigorous autoionization selection rules by l spoilage of the Rydberg electron. The effect appears accentuated for high J, low n * states (J ∼27, 28; n * ∼ 23) and quenches at J∼11, n * ∼ 37. The quenching is attributed to the onset of the Inglis-Teller effect. © 1990 American Institute of Physics.