ACTIVATION BARRIERS FOR SERIES OF EXOTHERMIC HOMOLOGOUS REACTIONS .3.REACTIONS OF S2 METAL ATOMS WITH N2O AND O2

Potential energy curves are derived for the rate-limiting channels of reactions of s2 metal atoms with N2O and O2, for which both reactants are in their ground electronic states. Activation barriers and rate co efficients are derived from these curves and are compared with the ava ilable experimental data. The importance of contributions by spin-forb idden channels to the rate coefficients of N2O reactions is evaluated using the Landau-Zener-Stuckelberg probability of potential-curve swit ching. Calculated rate coefficients thus obtained are in good agreemen t with the available experimental data. It is established that for the Mg, Ca, and Ba+N2O reactions the interaction energy of the lowest sin glet and triplet states increases as the mass of the metal atom increa ses. Spin-forbidden channels are thus more important for the Ca and Ba +N2O reactions than for the Mg+N2O reaction. Calculated activation bar riers for reactions of s2 metal atoms with O2 are found to be in agree ment with the available experimental data, the only exception being th at for the Zr+O2 reaction. The activation barriers, with the exception of those for the Ni and Zr+O2 reactions, are seen to correlate with t he s-p promotion energies plus the ionization potentials of the atoms. Explanations for these disagreements are given.