MOLECULAR BEAM CHEMILUMINESCENCE (CL) OF $Sm + N_{2}O$: TRANSLATIONAL AND INTERNAL ENERGY DEPENDENCE OF THE CL CROSS SECTION AND RATE CONSTANT

Abstract

The kinetic energy dependence of the visible CL of $SmO^{*}$ formed by the reaction Sm + $N_{2}O$ was determined using crossed molecular beams (a supersonic $N_{2}O$ beam, seeded with He, and a thermal effusive Sm beam) with two nozzle stagnation temperatures of 281 and $613^{\circ} K$. The CL cross section $\sigma {(E)}$ showed the two prototype excitation functions--the endoergic and exoergic types for the lower and higher temperatures, respectively. The different functionality is explained in terms of a simple collision theory which takes account of the reactant vibrational (bending mode) excitation. The CL gross rate constant was measured with the beam(SM) - gas $N_{2}O$ arrangement using a heatable scattering chamber $(300-600^\circ K$ ). The Arrhenius-type plot of the rate constant revealed a convex curve. This unusual behavior is also accounted for by the above simple model.