IRSPEC observations of planetary nebulae

We have obtained infrared spectra of planetary nebulae in the 3.0–3.8 m range using IRSPEC, the ESO grating infrared spectrograph, attached to the 3.6-m telescope. We find evidence of an evolution of the carriers of the unidentified emission bands in the 3 m region, and explain the observed behaviour in terms of ion irradiation from fast stellar wind.Based on observations collected at the European Southern Observatory, La Silla, Chile.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Univers, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.