Stopping anisotropy in molecular chains

Recently, we have addressed the effects of overall shape upon the electroni c response of isolated molecules and nanoclusters. with particular emphasis on the mean excitation energy. Here, we consider the relationship between gross molecular shape and mean excitation energy anisotropy for very long o bjects. In particular we compare results for elongated ellipsoids and a str ing of particles. We find the latter model gives a better prediction of sto pping power anisotropies of isolated long molecules. (C) 2000 Elsevier Scie nce B.V. All rights reserved.