Rydberg states ZEKE spectroscopy

The other source of congestion is due to the molecular core. It is most readily discussed using the inverse Bom-Oppenheimer point of view to define the zero-order quantum numbers. Here each state of the ionic core has its very own series of high Rydberg states. The physical reality of this approximation is the observation [36,43] of the long-time stable ZEKE states not just below the lowest ionization threshold but also just below the threshold of ionization processes that leave an excited ionic core. Indeed, it is for this very reason that ZEKE spectroscopy is useful for the spectroscopy of ions (or for such neutrals that are produced by ionization of negative ions... 

There can be a difference between the dissociation of polyatomic molecules and delayed ionization in the nature of the initial excitation. In ZEKE spectroscopy the state that is optically accessed (typically via an intermediate resonantly excited state) is a high Rydberg state, that is a state where most of the available energy is electronic excitation. Such a state is typically directly coupled to the continuum and can promptly ionize, unlike the typical preparation process in a unimolecular dissociation where the state initially accessed does not have much of its energy already along the reaction coordinate. It is quite possible however to observe delayed ionization in molecules that have acquired their energy by other means so that the difference, while certainly important is not one of principle. 

GENERAL DISCUSSION ON MOLECULAR RYDBERG STATES AND ZEKE SPECTROSCOPY PART I... 

ZEKE Spectroscopy, this volume) are obtained by ionizing the Rydberg series which is built on a particular state of the ionic core. The inverse Bom-Oppenheimer picture is thus natural when one begins the discussion with what is actually the raw observation. 

Prof. Schlag ( ZEKE Spectroscopy, this volume) has introduced a new sequential technique of ZEKE spectroscopy In the first step, a negative ion M is photoionized, yielding the neutral core M of the excited Rydberg state of the anion M. In the second step, M is further photoionized, yielding the cationic core M+ of the excited Rydberg state of the neutral molecule M. The overall sequence is thus... 

T. P. Softley The aims of ZEKE spectroscopy are conceptually different from the atomic pulsed-field ionization experiments that predate ZEKE. In the latter, the aim is always to observe and study the individual Rydberg states. In ZEKE spectroscopy the aim is to detect small batches of Rydberg states lying below successive vibration-rotation thresholds of the ion without specific interest in the individual Ryd-... 

FROM RYDBERG STATE DYNAMICS TO ION-MOLECULE REACTIONS USING ZEKE SPECTROSCOPY... 

---