Abstract: Geometrical structures of³² S¹⁶0₂ and³⁴ S¹⁶O₂ are optimized at B3P86/cc-PV5Z level using Gaussian03 program. Equilibrium geometry。vibrational and rotational constants etc.are obtained.Total internal partition functions(TIPF)of³² S¹⁶0₂ and³⁴ S¹⁶O₂ are calculated from 70 to 6000K Witll product approximation.Rotational partition sums adopt WATSON rigidmtator model and vibrational partition sums use harmonie oscillator approximation.It is found that calculated results are consistent with those offered by HITRAN database.and errors show linear correlation approximately from 70 to 3000 K.By fitting errors,TIPF were corrected at high temperatures range from 3000 to 6000 K.Corrected values are fitted to a four-order polynomial of T.and coefficients are evaluated. This allows a rapid and accurate calculation of TIPF at 3 000-6 000 K.

Key words: flue gas, SO₂, isotope, partition functions