Electronic energy partitioning in the reactions of metastable Mg*(3PJ) atoms with F2, Cl2, Br2, I2, ICl, IBr

Chemiluminescent reactions of metastable Mg*(P-3(J)) atoms with F-2, Cl-2, Br-2, I-2, ICl, IBr molecules were studied in a beam-gas experiment. For all homonuclear targets the MgX(A (2)Pi - X (2)Sigma(+)) emission was observed, but for ICl and IBr reactants the MgI(A-X) emission was absent and only MgCl(A-X) or MgBr(A-X) spectra were found. In addition, for the I-2, IBr, ICl, Br-2 reactions, broad pseudocontinua extend from above 400 nm into the infrared. These pseudocontinua are tentatively attributed to the MgI, MgBr(B' (2)Sigma(+) - X (2)Sigma(+)) transition. The total attenuation cross sections, chemiluminescence cross sections and quantum yields were measured. The quantum yields are all below 5%. The results are analyzed using information theory. The low yields for the Mg* + F-2 system are explained by a barrier in the entrance channel. For other reactions the low yields are most probably caused by predissociation of the MgX*(A (2)Pi) products.