The AMIGA sample of isolated galaxies: III IRAS data and infrared diagnostics

Aims. We describe the mid- (MIR) and far- (FIR) infrared properties of a large (-1000) sample of the most isolated galaxies in the local Universe. This sample is intended as a "nurture-free'' zero point against which more environmentally influenced samples can be compared.Methods. We reprocess IRAS MIR/FIR survey data using the ADDSCAN/SCANPI utility for 1030 out of 1050 galaxies from the Catalogue of Isolated Galaxies (CIG) as part of the AMIGA project. We focus on diagnostics (FIR luminosity $L_{\rm FIR}$, $R=\log(L_{\rm FIR}/L_{B})$, and IRAS colours) thought to be sensitive to effects of environment or interaction.Results. The distribution of $\log(L_{\rm FIR})$ sharply peaks from 9.0-10.5, with very few (