We have recently obtained high resolution IR spectra (λ/δλ ≈ 1000) of the planetary nebula Hb 5, over the range 1.6–1.75 μm and 3.1–3.75 μm (Magazzù & Strazzulla 1992) at the European Southern Observatory (ESO). Emission bands have been detected the most prominent being at 3.3, usually attributed to PAH molecules, and 3.4 μm. For the predicted (de Muizon et al. 1986) first armonic (at 1.67 μm) of the 3.3 μm band we get an upper limit at least 45 times weaker than the 3.4 μm feature. This, together with the high ratio of fluxes F3.4/F3.3, challenges the hypothesis that the 3.4 μm band is the first hot band. We suggest that the first hot band may be identified with a small feature at 3.46 μm. In this case the first armonic would fall at 1.686 μm where we detect a small feature.