  We present results from an ongoing survey of the infrared emission lines [Kr
III] 2.199 and [Se IV] 2.287 micron in Galactic planetary nebulae (PNe).
Krypton and selenium may be produced by slow neutron-capture nucleosynthesis
(the ``s-process'') during the asymptotic giant branch (AGB) phase of PN
progenitor stars, and brought to the surface by convective dredge-up before PN
ejection. We detect emission from Se and Kr in 65 of 114 Galactic PNe, and use
the line fluxes to derive ionic abundances. We employ ionization correction
factors based on coincidences of ionization potentials to calculate total
elemental abundances, and discuss photoionization models designed to test the
veracity of these corrections. The derived Se and Kr abundances of our targets
range from approximately solar to enriched by a factor of 5, which indicates
varying degrees of dredge-up and s-process efficiencies in the progenitor
stars. In PNe exhibiting emission from both Se and Kr, we find that the
relative abundances of these elements are generally in agreement with
predictions from theoretical models of s-process nucleosynthesis. We examine
our results for correlations between s-process enrichments and other nebular
properties, such as CNO abundances, morphology, and characteristics of the
central stars. PNe with Wolf-Rayet central stars tend to exhibit more elevated
Se and Kr abundances than other nebulae. Bipolar nebulae, believed to arise
from the most massive of PN progenitors, may have lower n-capture abundances
than elliptical PNe.
