The dynamics of predissociating high Rydberg states of NO

In this paper we present a theoretical study of the predissociation dynamics of the nf(N+ = 2) (with the principal quantum numbers n=40-95) and the np(N+=0) (n=70-125) Rydbrg series of NO, which exhibit a marked lifetime dilution (lengthening) at n > 65 for the f series and at n > 116 for the p series [M.J.J. Vrakking and Y. T. Lee, J. Chem. Phys. 102, 8818 (1995)]. The multichannel effective Hamiltonian with several doorway (for excitation) and escape (for decay) states was constructed using experimental information on the quantum defects and on the decay width constants incorporating both intramolecular coupling and exterior electric field coupling between high Rydbergs. The analysis of the intramolecular Rydberg electron-core dipole long range coupling (H-R-D) in conjunction with the energy gaps between proximal pairs of energy levels, which are subjected to appropriate selection rules, reveals that (i) for low l(less than or equal to 3) core-penetrating Rydbergs only a small number of accidental near-resonances are exhibited, and (ii) for high l(>3) nonpenetrating Rydbergs the electron-core dipole coupling decreases fast with increasing l, i.e., (H-R-D)proportional to l(-7). The general characteristics of the high l(>3) manifold establish a bottleneck effect, which precludes intramolecular l mixing, implying that high Rydberg lifetime dilution effects can be induced only by exterior electric field coupling (H-STARK). Parameter-free multichannel effective Hamiltonian calculations were conducted under narrow-band excitation conditions, which interrogate the electric field induced mixing in the energetic vicinity of the doorway state. The electric field induced l mixing model accounts semiquantitatively for the electric field dependence of the energy-resolved line shapes of the nf(N+=2) series and for the n and electric field dependence of the lifetimes of the nf(N+=2) and the np(N+=0) series. Accidental near-resonant simultaneous intramolecular and electric field coupling [GRAPHICS] for two sets of proximal states n=92, n'=80 and n=95, n'=82, result in mediated-sequential mixing, which is manifested by slow decay times below the onset of effective electric field mixing by weak (F-0 similar or equal to 0.04-0.08 V/cm) stray electric fields. (C) 1996 American Institute of Physics.