Electric Field Effects on Long Living ZEKE States

Abstract

The effect of an electric field on the overall intensity of the ZEKE spectrum and on the lifetime is discussed for very long living states detected by a pulsed field ionization delayed by several microseconds or more. It is shown that the presence of a dc electrical field can shorten the very long lifetimes and that it can also reduce the overall intensity of the very long living states. The decrease in the long lifetimes of the ZEKE states is complementary to the field-induced elongation of the shorter lifetimes. The discussion is based on quantum mechanical considerations and is illustrated by detailed computational studies, for a model problem, using an effective Hamiltonian formalism for an energy range just above the lowest ionization threshold. The model allows for coupling of different Rydberg series built on different excited states of the core where the continuum corresponds to the ground state. Predissociation is not allowed for in the model Hamiltonian. The trends are in accord with the observations of Held et al. as reported in the preceding paper, and the magnitude of the measured lifetimes of the ZEKE states (dozens of microseconds) are reproduced by the computations.

Decay Dynamics of the Predissociating High Rydberg States of NO

“…ZEKE (zero electron kinetic energy) spectroscopy − has provided valuable insight into the dynamics of high atomic and molecular Rydberg states. − In ZEKE spectroscopy, the lifetimes of high Rydberg states have been found to be orders of magnitude longer than what was expected by extrapolating the lifetimes at low n using an n 3 scaling law and extremely sensitive to external perturbations such as an external dc field, an external magnetic field, or the presence of neighboring ions. The role of the external dc field in diluting the coupling strength to the decay channels over the entire l manifold and increasing the lifetime was early on pointed out by Bordas and Chupka , and then studied in more detail. − The lifetimes of high molecular Rydberg states are also considerably enhanced by collisional effects and the presence of a magnetic field. ,,,− Moreover, experimentally, the decay kinetics of the ZEKE intensity very often exhibits a bimodal character, ,, with a prompt and a delayed component. This bimodal decay of the ZEKE intensity was also recovered theoretically both from a kinetic model and from dynamical computations. − …”

“…The role of the external dc field in diluting the coupling strength to the decay channels over the entire l manifold and increasing the lifetime was early on pointed out by Bordas 25 and Chupka 26,27 and then studied in more detail. [28][29][30][31][32][33][34][35][36][37] The lifetimes of high molecular Rydberg states are also considerably enhanced by collisional effects and the presence of a magnetic field. 3,15,18,[38][39][40][41][42][43][44] Moreover, experimentally, the decay kinetics of the ZEKE intensity very often exhibits a bimodal character, 17,45,46 with a prompt and a delayed component.…”

Photoselection and the Appearance of Franck−Condon-Forbidden Thresholds in the ZEKE Spectrum of NO2

“…14,15,[17][18][19] Numerous studies have shown evidence of Rydberg-Rydberg coupling involving transfer of energy and angular momentum between Rydberg-orbital and core-rovibrational degrees of freedom, [20][21][22][23][24][25][26][27][28] but most workers now agree that the dominant mechanism for lifetime lengthening lies in the field-induced evolution of the Rydberg electronic degree of freedom in the nonpenetrating space of high l and m l . [29][30][31][32] In earlier work, we used three-color rovibrational selection to study the ZEKE spectrum of NO 2 in strong vertical 3pσ Rydberg-to-threshold transitions. 33 Our results characterized the rotational and vibrational structure of the cation, including a moderate bend-stretch Fermi resonance, 34 which is present to virtually the same degree in the cation core of the originating 3pσ Rydberg state.…”

Autoionization rates of core-excited magnesium Rydberg atoms in electric fields using the core fluorescence as a reference

“…This behavior is consistent with the observation that the discrete structure observed in the spectra below n = 80 corresponds to a purely hydrogenic Rydberg series with zero quantum defect (see also discussion in Refs. [41][42][43][44]).…”