Activated chemisorption of Ch 4 and internal molecular motions

Abstract

Measurements have been made of the sticking coefficient for methane at different gas temperatures chemisorbing on freshly evaporated films of rhodium kept at 0 ° C. The activation energy of 11 kcal/mol found in these experiments for chemisorption directly from the gas phase exceeds by far the value of 5 kcal/mol, reported previously for chemisorption when gas and film are isothermal. The difference is in quantitative agreement with the independently known desorption energy of molecularly bound methane from rhodium. This result is expected if the energy of internal molecular motions, rather than translational energy, is most effective in facilitating activated chemisorption in this system.