Study of IR laser photoacoustic spectra of organic molecules adsorbed on metal surface

Using a branch-tuning CW CO2 laser in the range of 0.2 to 10.8 microns, the IR photoacoustic spectra of organic molecules absorbed on a silver surface were studied. The absorbed molecular spectra of four layers of arachidic acid and cellulose diacetate with different surface densities was studied. No peak shift was found in a comparison between IR photoacoustic spectra of solid arachidic acid near 944/cm and the corresponding IR Fourier spectra of solid archidic acid. The IR photoacoustic spectra of cellulose diacetate with sigma sub 1 = 14,000/sq cm and sigma sub 1 = 5.5 x 10 to the 15th/sq cm respectively was compared with the corresponding transmission spectra of solid cellulose diacetate. It was found that the peak of the former near 1054/cm had a red shift of about 5/cm while the peak of the latter had no obvious shift within the range of accuracy of the experiment.