ROLE OF VIBRATIONAL ENERGY IN SURFACE ISOMERIZATION OF CYCLOPROPANE

We report an investigation of the heterogeneous isomerization of cyclopropane to propylene on mica surfaces under conditions which made possible the independent variation of surface temperature, as well as the velocity and vibrational temperature of the incident cyclopropane molecules. Measured reaction probabilities ranged from 3.4 × 10-6 to 5.4 × 10-4 as the vibrational temperature was increased from 700 to 820 K while the surface temperature was constant at 756 K. This dependence upon vibrational temperature corresponds to an activation energy of 56 kcal mol. The apparent activation energy corresponding to a similar variation in surface temperature is 21 kcal mol. Model calculations indicate that these results cannot readily be accounted for in terms of simple energy exchange between the surface and a reactant molecule We conclude that the overall process must involve activated adsorption followed by surface reaction and desorption of product propylene. © 1979.