Before revision: If these sites are not occupied, molecules do the following (with probability in parentheses): adsorb on the surface chemically () desorb from the surface () move to the next precursor state () and if these sites are occupied, they desorb from the surface () move to the next precursor state () Note that an occupied site is defined as one where there there is a chemically bonded adsorbate so by definition it would be .
After revision: If these sites are not occupied, molecules do the following (with probability in parentheses): adsorb on the surface chemically () desorb from the surface () move to the next precursor state () and if these sites are occupied, they desorb from the surface () move to the next precursor state () Note that an occupied site is defined as one where there is a chemically bonded adsorbate so by definition it would be .