Langlois et al. [Appl. Phys. Lett. 87, 131503 (2005)] have demonstrated that the etch yield of SrTiO3 films in Ar/SF6 plasmas decreases as the concentration fraction of molecular ions in the plasma increases. Introducing the concept of effective mass for both ions and SrTiO3, these experimental results have quantitatively been explained in the framework of a well-established model originally developed to describe the sputtering of single-atom materials by nonreactive monoatomic ions. This model has, however, ignored the dissociation of molecular ions occurring as these particles impact the material surface. In the present article, the influence of the positive ion composition on the ion-assisted chemical etch yield of SrTiO3 films in Ar/SF6 plasmas is reexamined to the light of this consideration. A rate model accounting for the dissociation of the various molecular ions is proposed and validated using experimental data. It is found that even though a specific ion species may not be the most important charge carrier in the plasma, its contribution to the plasma etching dynamics may still be the most significant. (C) 2007 American Vacuum Society.