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Certain theoretical predictions are presented for the preferential population of final states with angular momentum l' in collisions involving an initially excited atom. Varying l', we find that the maxima of both the inelastic form factors and cross sections for the nl yields n'l' transitions in hydrogen, induced by collision with electrons and heavy particles, in general oscillate on a background which rises as l' is increased, until they both attain a pronounced peak at a unique value l' sub max which is strongly dependent on only the initial principal quantum number n and which is fairly insensitive to changes in l and n'. An expression for l' sub max is derived. For l' >l' max, the form factors and associated cross sections exhibit a dramatic decline, resulting in negligible population of those states. The predictions differ from those suggested by the Bethe high-energy asymptotic limit which favours dipole transitions, and assume significance in situations where excited states are important as in laser modelling, astrophysical and fusion plasmas, and in laboratory studies of excited Rydberg states. For heavy-particle (nl yields n'l') collisional transitions the additional undulations which appear in the cross sections over a wide energy range are predicted and explained.