where v is the pre-exponential factor of the desorption rate coefficient, he condensation coefficient (defined as the fraction of those molecules that are adsorbed with an activation energy greater than the energy of activation for adsorption Ea), m is the mass of the adsorbate molecule, k is the Boltzmann constant and Q the heat of adsorption (the difference between the activation energies Ed and Ea necessary for desorption and adsorption, respectively).