This volume offers a timely look at Rydberg states of atoms in external fields and dielectronic recombination. Each topic provides authoritative coverage, presents a fresh account of a flourishing field of current atomic physics and introduces new opportunities for discovery and development. Topics considered include electron-atom scattering in external fields; observations of regular and irregular motion as exemplified by the quadratic zeeman effect and other systems; Rydberg atoms in external fields and the Coulomb geometry; crossed-field effects in the absorption spectrum of lithium in a magnetic field; precise studies of static electric field ionization; widths and shapes of stark resonances in sodium above the saddle point; studies of electric field effects and barium autoionizing resonances; autoionization and dielectronic recombination in plasma electric microfields; dielectronic recombination measurements on multicharged ions; merged beam studies of dielectronic recombination; Rydberg atoms and dielectronic recombination in astrophysics; and observations on dielectronic recombination.
Experimental details are presented for the measurement of the effects of extrinsic electric fields on cross sections and Rydberg product-state distributions for dielectronic recombination of
Mg+ with electrons. A new type of Rydberg state detector is described. Experimental results for dielectronic recombination in the presence of fields are presented for three field values, and these results are compared with theoretical calculations.
It should be possible to separate experimentally the contributions to dielectronic recombination (DR) of energetically unresolved intermediate autoionizing Rydberg
nl states using electric fields. This notion is based on two essential ideas. First, electric fields enhance the DR rate by Stark-mixing low-
l states with high autoionization rates with high-
l states with low autoionization rates. Second, the field at which an
l state becomes Stark mixed is determined by its quantum defect, a known function of
l. Consequently, the electric-field dependence of the DR rate should reflect the
l dependence of the autoionization rates and thus the contributions of the zero-field
nl states to the DR rate. This notion cannot be tested experimentally by examining true DR. However, it can be tested by studying DR from a continuum of finite bandwidth (CFB), for in this case the intermediate Rydberg
nl states are restricted to a single value of
l. Specifically, we have examined the electric-field dependence of DR from two CFB's, the
Ba6p3∕211d and
6p3∕28g states. In these two cases the intermediate autoionizing Rydberg states are restricted to the
Ba6p1∕2nd and
6p1∕2ng states
(l=2and4), which have quantum defects of 0.25 and 0.02, respectively. For the same
n they are Stark mixed at fields differing by an order of magnitude. We show experimentally that enhancement of the DR rate occurs at fields differing by a factor of 10 for
nd and
ng states of the same
n, as expected, confirming that the field dependence of DR can be used to extract information about the contributions of energetically unresolved
l states to the zero-field DR rate.