Semiempirical configuration interaction (SECI) theory is used to predict activation barriers E, as defined by k(T)=AT(n) exp(-E/RT). Previously SECI has been applied to homologous series of oxidation reactions of s(1), s(2), and s(2)p(1) metal atoms. Here it is extended to oxidation reactions of diatomic molecules containing one s(2)p(1) atom. E values are calculated for the reactions of BH, BF, P BCl, AlF, AlCl, AlBr, GaF, Gal, InCl, InBr, InI, TlF, TlCl, TlBr, and TlI with O-2, CO2, SO2, or N2O. These values correlate with the sums of the ionization potentials and Sigma-Pi promotion energies of the former minus the electron affinities of the latter. In the earlier work n was chosen somewhat arbitrarily, which affected the absolute values of E. Here it is shown that examination of available experimental and theoretical results allows determination of the best values of M. Using this approach yields n=1.9 for the present series. For the seven reactions which have been studied experimentally, the average deviation of the SECI activation barrier prediction from experiment is 4.0 kJ mol(-1). Energy barriers are calculated for another 52 reactions. (C) 1997 American Institute of Physics.