Resonance Raman spectra of monolayers of transition metal phthalocyanines reveal specific interaction with the support. To elucidate its mechanism, Raman spectra of zinc phthalocyanine monolayers were studied. The analysis was based largely on the results of MNDO calculations. Calculated wavenumbers turned out to be in good agreement with the experimental results. It seems plausible that the α-nitrogen atoms dominate the interaction with the support. Calculation results also show that the usually assumed D4h geometry does not represent the true energy minimum but must be considered as the mean of two mesomeric forms.