Electronic branching ratios in the chemiluminescent reactions of Sr(1S) and Sr∗(3P, 1D) atoms with ICl and IBr

The chemiluminescence of strontium monohalides formed in the reactions of ground state Sr(5s2 1S) and discharge-excited metastable Sr∗(5s5p 3P, 5s4d 1D) atoms with ICl and IBr was studied in a beam-gas arrangement. For the Sr(1S) reactants, only strontium monochloride and monobromide emission could be observed; the latter indicates that D0(SrBr) ⩾ 336 kJ/mol. Collisions of metastable strontium atoms with the interhalogens produced both monohalides in the A 2Π, B 2Σ+ and C 2Π states. The electronic branching ratios have been determined with relatively high precision, but absolute values of chemiluminescence cross sections have not been measured. The branching into the (A + B) exit channels of chemically different strontium monohalides was found to be statistical, while for the C states it shows a deviation.