TEMPERATURE-DEPENDENT PHOTOACOUSTIC-SPECTROSCOPY WITH A HELMHOLTZ RESONATOR

GO-laser photoacoustic spectroscopy (PAS) is introduced to monitor the absorption of fatty acid vapors in the temperature range between 280 and 350 K. Since, the absorption as well as the photoacoustic (PA) sig nal depend on temperature, simultaneous transmission measurements have been performed to calibrate the PA signal at every temperature. A spe cial PA cell acting as a Helmholtz resonator has been constructed fulf illing the requirements for temperature-dependent PA measurements. The results of numerical calculations of the acoustic properties of the P A cell are compared with experimental measurements with respect to the frequency response, the quality factor of the cell and the temperatur e dependence of the cell constant. As an example, the analysis of the obtained absorption spectra of deuterated acetic acid, which were reco rded with this set-up, revealed the dimerization enthalpy Delta H and entropy Delta S as well as the integrated band absorbances of the C=O- vibration of the monomer and dimer molecules at CO-laser wavelengths.