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In the present work a positive secondary ion emission from a silicon produced by Au m Ϫ projectiles (m ϭ 1-3) with energies of E 0 ϭ 9 and 18 keV and by Al m Ϫ projectiles (m ϭ 1,2) with energies of E 0 ϭ 6, 9, 12, and 18 keV have been studied. Anomalous high nonadditivity of sputtering as large cluster Si n ϩ ions (n Ͼ 4) under molecular Au m Ϫ ion bombardment has been found. As compared with heavy (Au m Ϫ ) projectiles, the light (Al m Ϫ ) projectiles are not effective for sputtering of large cluster ions. For molecular Al m Ϫ ion bombardment nonadditivity of sputtering of small cluster Si n ϩ ions (n Յ 4) increases with decreasing of the energy E 0 from 9 to 6 keV/atom. This effect shows that the efficiency of nonadditive sputtering strongly depends on the penetration depth of molecular projectile and, hence, on the energy density deposited by molecular projectile into subsurface layers of the target from which the cluster ion emission occurs. (Int J Mass Spectrom 209 (2001) 141-152)