Federation Quantitative spectral analysis of surface adsorption sites is not possible without the knowledge of absorption coefficients of test molecules. Both quantum chemical calculations and electrostatic approach predict the correlation between the frequency shifts on adsorption, ionic radii of the cations and the integrated absorption coefficients. We have shown that some diatomics, such as CO, reveal linkage isomerism and form with the cations or OH-groups in zeolites, besides the usual C-bonded complex with the frequency shifted to higher wavenumbers, the energetically unfavorable O-bonded with the frequency lowered with respect to gas phase. The latter species coexists in the thermodynamic equilibrium with the C-bonded form and has negligible concentration at liquid nitrogen temperature. Surface isomeric states were also established for some other adsorbed species, such as cyanide ion CN ^- produced by HCN dissociation. The existence of linkage isomerism can be explained by a simple electrostatic model, which takes into account the interaction of molecular quadrupole with the cations. Besides the linear configurations with positively charged sites, the model predicts formation of side-on complexes of CO and N ₂ with surface anions, in agreement with many experimental results.