Effects of Indirect Correlations between Attracted Particles on the Adsorption and Desorption Rates during Physical Adsorption

The effects of indirect correlations between the nearest adsorbed particles attracting each other on the rates of the elementary adsorption and desorption stages were studied. The calculation was performed within the framework of the theory of absolute reaction rates, including the difference between the interactions of particles in the ground states and the activated complex of the stage in the transition state. The local particle distributions were calculated within the framework of the cluster variation method (CVM), which allows us to go beyond the quasichemical approximation (QCA), reflecting the effects of only direct correlations or an isolated pair (2 × 1) in CVM terminology. The isothermal concentration dependences of the adsorption and desorption rates of adsorbed particles on the homogeneous (100) flat face, as well as the thermal desorption spectra, were calculated. The rates calculated for some simplest basic clusters (2 × 2, k1s, 3 × 3, 3 × 4) were compared with those calculated in QCA. At temperatures below the condensation temperature of the adsorbate, the effects of separation of the latter into two coexisting phases were taken into account. Inclusion of indirect correlations in calculation for increased basic cluster sizes leads to quantitative differences between the given cluster approximation and QCA, while the type of the concentration dependence of the adsorption/desorption rate and the thermal desorption spectrum remains qualitatively unchanged.