Quasiclassical trajectory studies of energy transfer for a number of atom-diatomic molecule systems employing semiempirical (valence-bond) potential- energy surfaces are presented. The systems studied include: I + H2, Cl + H2, Cl + HCl, H + HCl, F + HF, F + DF, H + HF, D + HF, H + DF, D + DF, I + I2, Cl + Cl2, H + HBr, and Br + HBr. 10 figures, 16 references. (GHT)