s and d Rydberg series of NO probed by double resonance multiphoton ionization

Abstract

The s and d Rydberg states of NO with v = 0 have been observed for 6 leqslant; n* leqslant; 40 by double resonance multiphoton ionization which was three-photon resonant with the 3pπC ²∏ (v = 0) Rydberg intermediate state. Strong parity selection is shown to occur in the intermediate level despite the fact that the Λ-doublets are not resolved. The OODR spectra are thereby considerably simplified. A unified description of the rotational-electronic structure of the s and d Rydberg states in terms of quantum defect theory is presented, extending from the low n* s, d supercomplexes up beyond the ionization threshold. Electronic radial dipole transition moments are calculated and included in the MQDT analysis, giving evidence for a Cooper minimum in the region of the supercomplex n* = 5. For 25 leqslant; n* leqslant; 40 fringes are observed in the OODR spectrum and are interpreted in terms of rotational l-uncoupling, electronic s ∼d mixing and energy dependent electronic dipole transition moments. The fringe formation is shown to have a different origin than the stroboscopic effect observed in Na₂ by Labastie et al. Above n* = 35 the Stark induced p series appears and is also interpreted quantitatively.