Determination of absolute photon yields under single-collision conditions

Abstract

The experimental procedure is presented to measure the absolute photon yield, the percentage probability of emitting a visible photon per reactant molecule consumed, for chemiluminescent reactions under single-collision conditions. Using a well-defined metal beam directed into a scattering gas at submillitorr pressures, this procedure is applied to the reactions Sm+N2O, Sm+F2, Ba+N2O, and Ba+NO2 to obtain the photon yields in the 350–800 nm range of 0.39%, 11.8%, 2.4%, and 0.18%, respectively, where the estimated uncertainty is about 50%. The absolute photon yields for each of these reactions initially increases with scattering gas pressure, demonstrating that secondary collisions ’’feed’’ radiating states from dark, reservoir states. It is suggested that other relative photon yields can be put on an absolute basis by comparison with the Sm+N2O chemiluminescent reaction.