Various mathematical models are used for investigation of the thermal desorption spectra (TDS spectra) of hydrogen isotopes, in particular, in the form of a first-order reaction for the volume-averaged concentration (in the case of diffusion limitation), second-order models (taking into account the recombination of hydrogen atoms on the surface into molecules) and more detailed models reflecting multistage transport (volume diffusion, outlet to the surface, recombination, desorption). Interest is the analysis of the structure of the spectrum in order to identify the causes and "driving forces" of a physical and chemical nature corresponding to each peak. The article presents an analysis of the symmetry of unimodal TDS spectra and the results of simulation.