Revise the Langmuir isotherm equation to allow for the dissociation of a molecule

into two parts upon adsorption. Hint: dissociation means that a molecule $A_2$ will

occupy two sites on adsorption, i$.$e$.,A_2($g$)+S2($A$-$S$)($ads$.),$ where $"S"$

indicates sites. The probability of two adjacent vacant sites on the surface is

proportional to the square of the concentration of vacant sites, $(1-{)}^2.$ The

same logic can be applied for desorption from the surface.