Thermochemical processes accompanying the formation of gaseous molecules SrF g at the electrothermal determination of fluorine via the molecular absorption were investigated using equilibrium thermodynamic modeling. The algorithm of modeling was developed. For carrying out the calculations non-equilibrium thermodynamic system realized in graphite furnace was divided into serial quasi-equilibrium thermodynamic subsystems. These subsystems correspond to the major stages of temperature-time program: drying of the sample, pyrolysis, vaporization and gaseous dimer molecule formation. Original chemical compound of thermodynamic subsystems during modeling, method for its realization and treatment of calculated data were recommended for each stage. The evaluation of modeling accuracy was carried out using published experimental data and the results of our own experiments. Theoretically according to our experimental cases of mixed and separated injection of Sr(NO 3) 2 and NaF solutions on different area platform of graphite furnace were examined. The carried out calculations made it possible to establish the composition of condensed residues after stages of drying and pyrolysis, gas phase composition of the analytical zone of graphite furnace at the stage of evaporation and molecules formation. It has been established that molecules SrF g formation happens due to thermal decomposition of condensed SrF 2 c for the mixed injection of solutions and interaction gaseous compounds of fluorine with Sr g for the separated injection of solutions. The proposed algorithm may be used for research of other dimer molecules formation in a graphite furnace. The results of modeling may be useful for the selection of temperature-time program of heating, method of calibration, increasing the sensitivity and accuracy of halogens determination.