Based on general equations of hydrodynamics we describe the processes in a photoacoustic cell. The results of modeling a 1-D photoacoustic cell in computer simulations well agree with the experiment. Based on this effect we have developed a highly sensitive IR spectrometer/gasanalyzer "IKS-GAS" having the threshold sensitivity at the level of 3 by 10–10 cm–1 in the operation mode of a continuous flow of a sample under study. In the case of strongly absorbing gases (in the region 9.2 to 10.8 mm) that corresponds to their concentration of 10–10 percent by volume.