MULTICHANNEL QUANTUM-DEFECT THEORY STARK-EFFECT CALCULATION OF AUTOIONIZATION LIFETIMES IN HIGH-N RYDBERG STATES OF AR, N-2 AND H-2

Multichannel quantum defect theory simulations of excitation spectra t o autoionizing high-n Rydberg states (n = 13-150) are presented for Ar (spin-orbit autoionization), H-2 (vibrational autoionization) and N-2 (rotational autoionization), including the l-mixing due to homogeneou s electric fields (Stark effect). The calculations, the first of their kind relevant to the ZEKE (zero-kinetic energy) photoelectron spectro scopy excitation range, are compared with previously published experim ental results. Although in some cases the lifetimes derived from calcu lated Linewidths are sufficiently long for the states to be observed b y delayed pulsed-field ionization, they are generally found to be too short in the highest-n regions (n > 80) to account for the very long l ifetimes observed experimentally (tau > 10 mu s), pointing to the impo rtance of alternative stabilization mechanisms. The effects of rotatio nal channel couplings in H-2 and N-2 are investigated; these are very weak if both channels are above the Inglis-Teller limit, but show sign ificant effects if only one channel is strongly l mixed. In H-2 it is found that a window resonance is preserved in the presence of a strong field. In Ar, ortho-H-2 and N-2 fine-structure of the hydogenic manif olds is predicted, and the distribution of intensity and linewidth amo ngst the fine-structure components is investigated. The non-zero quant um defects cause a lifting of degeneracy in the manifolds between diff erent m(l) components. It is proposed that this would cause a reductio n in m(l)-mixing by inhomogeneous fields as the homogeneous field incr eases. (C) 1997 American Institute of Physics.