An analytical model is described in which the time‐averaged charge of adsorbed particles is a function of the energy of transition between atomic and ionic states, as in a thermally ionized gas. This relation is used to determine the dipole moment of the adsorbed layer, including the effect of depolarization by adjacent charges. An expression is obtained which relates the emission properties to the temperature, degree of surface coverage, and basic properties of the substrate and adsorbate. Through estimation of the atom adsorption energy, a relationship is obtained which gives a good correlation of most available data for the emission properties of surfaces immersed in cesium vapor.