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The 3.3 mum emission band and the continuum at 3.2 mum have been mapped on a 9 x 4’ area in the direction of the H II region-molecular cloud interface M 17 south-west, with a 30" beam. In addition, the 3.4 mum feature has been measured along a single east-west strip. The results show that the 3.3 mum emission band intensity traces a ridge between the H II region and the molecular cloud, whereas the 3.2 mum continuum is emitted in the H II region and shows a spatial distribution which is similar to the 10 mum continuum. Assuming that the 3.3 mum band is due to polycyclic aromatic molecules (PAHs), and taking into account the effect of dust extinction within the complex on the measured 3.3 mum intensity and on the ultraviolet content of the heating radiation field, we have estimated the abundance of the 3.3 mum emitter. The results show that the 3.3 mum emitting material is located in the direction of the molecular cloud and is practically absent from the H II region. Comparing our data with larger beam measurements, we show that except for the H II region, the fraction of the total infrared flux radiated in the 3.3 mum band is roughly constant throughout the complex and equal to 6 10(-4). Concerning the origin of the 10 mum continuum toward the H II region, we show that it can neither be explained by the heating of standard dust grains with Lyman alpha trapped photons, nor with dust cocoons around B stars. Instead, we use the dust model of Desert et al. (1990) which includes PAH and very small grains in addition to the classical dust grains, and we are able to fit the whole infrared available data from 2 mum to 100 mum, both for the H II region and for the molecular cloud. We assume that the emission arises respectively from the neutral clumps embedded in the ionized gas and the warm envelopes of the molecular clumps. We use a standard dust-to-gas mass ratio and only adjust the strength of the 3.3 mum band. The quasi-absence of 3.3 mum emission from the H II region and the strong near infrared emission from 2 to 20 mum, demonstrate the existence of very small particles, 3 to 12 angstrom, in this direction. Those may be fully de-hydrogenated PAHs or some other kind of particles resulting from the disruption of the bigger grains in the shocks associated to the star forming activity.