DETERMINATIONS OF BOND-ENERGIES BY TIME-OF-FLIGHT SINGLE-COLLISION CHEMILUMINESCENCE

A pulsed beam of metastable atoms traverses a scattering chamber filled with oxidant gas at low pressures (beam + gas arrangement); the resulting chemiluminescence is spectroscopically resolved as a function of time to yield a time-of-flight (TOF) spectrum for different internal states. From this data, the initial relative translational energy distribution is derived for the reactants that populate the excited internal state observed. Lower bounds are placed on the barium halide (BaX) dissociation energies, using the reactions Ba(3D) + X2 → BaX* + X, where X = Br, I. Arguments are presented to show that these lower bounds represent measurements of the true bond energies: it is concluded that D00(BaBr) = 85.8 ± 2 kcal/mole and D00(BaI) = 72.9 ± 2 kcal/mole. The present work corrects previous determinations of bond energies from single-collision chemiluminescent studies which were in error because of unrecognized metastable contamination in the high-temperature atomic beam. © 1978.