Previous works have shown that atomic fluorine is the main etching agent of organic polymer surfaces subjected to fluorinated plasma treatments. In this work the etching probability per F atom impinging on a polymer-like material (hexatriacontane C36H74, a model molecule for high density polyethylene) has been estimated from direct measurements of the etching rate using a quartz crystal microbalance and from the absolute F atom concentration using threshold mass spectrometry. This etching probability has roughly the same value as the sticking probability of F atoms on this surface, which is in the range of 1%–3%. It has been pointed out that the reactivity of the surface with respect to F atoms is enhanced when the polymer surface is seen by the plasma. This could be due to either ions or vacuum ultraviolet (VUV) radiation. To more fully understand this point, we have built an external independent VUV source to irradiate the sample and we have used threshold ionization mass spectrometry to monitor the F atoms kinetics. The simultaneous irradiation of the substrate by VUV increases by a factor of 2 the reactivity of the substrate with respect to F atoms. © 2001 American Institute of Physics.