  Context. Fast-moving knots (FMK) in the Galactic supernova remnant Cassiopeia
A consist mainly of metals and allow to study element production in supernovae
and shock physics in great detail. Aims. We work out theoretically and suggest
to observe previously unexplored class of spectral lines -- metal recombination
lines in optical and near-infrared bands -- emitted by the cold ionized and
cooling plasma in the fast-moving knots. Methods. By tracing ion radiative and
dielectronic recombination, collisional $l$-redistribution and radiative
cascade processes, we compute resulting oxygen, silicon and sulphur
recombination line emissivities. It allows us to determine the oxygen
recombination line fluxes, based on the fast-moving knot model of Sutherland
and Dopita (1995b), that predicts existence of highly-ionized ions from
moderate to very low plasma temperatures. Results. The calculations predict
oxygen ion recombination line fluxes detectable on modern optical telescopes in
the wavelength range from 0.5 to 3 microns. Line ratios to
collisionally-excited lines will allow to probe in detail the process of rapid
cloud cooling after passage of a shock front, to test high abundances of O V
and O VI ions at low temperatures and measure them, to test existing
theoretical models of a FMK and to build more precise ones.
