Using photothermal deflection spectroscopy (PDS), vibrational overtone spectra have been obtained in organic thin films for the first time. Overtone and combination resonances for several orders above the fundamental are observed. The frequencies, relative intensities, and linewidths can be precisely determined. Assignments to specific CH bond resonances are made using the theory of anharmonic vibrations based on a Morse potential for local modes. Details of the molecular potential can be studied, as can be transition from normal to local made behavior. © 1990.