Using a branch-tuning CW CO2 laser in the range of 9.2μm to 10.8μm we have studied the IR laser photoacoustic spectra of organic molecules adsorbed on the surface of silver. The adsorbed molecular spectra of four layers of arachidic acid and cellulose diaoetate with different surface densities have been studied. No peak shift was ound in the comparision between the IR photoacoustic spectra of four layers of arachidic acid near 944cm-1 and the corresponding IR Fourier spectra of solid ar-achidic acid. For the IR photoacoustic spectra of cellulose diacetate with σ1=1.4×10 15 cm-2 and σ2=5.5×10 15 cm-2 respectively, we compared them with corresponding IR transparent spectra, of solid cellulose diacetate. It has been found that the peak of tlie former near 1054 cm-1 has a red shift about 5 cm-1 and the peak of the later has no obvious shift within the accurancy of the experiment.