Theoretical studies of partition functions of flue gas SO2 isotope

The geometrical structure of flue gas (SO2)-S-32-O-16 and (SO2)-S-34-O-16 molecule have been optimized at B3P86/cc-PV5Z level using Gaussian03 program, we gain theirs equilibrium geometry, resonance frequency and rotational constants et al.. The total internal partition functions are calculated at the temperatures from 70 K to 6000 K for (SO2)-S-32-O-16 and (SO2)-S-34-O-16 with the product approximation. Thereinto, the rotational partition sums Q(rot) adopt the WATSON rigid rotator model, which take into account centrifugal distortion corrections. The vibrational partition sums Q(vib) use the harmonic oscillator approximation model. It is found that the calculated total internal partition functions are consistent with those offered by HITRAN database from 70 K to 3000 K, and the errors shows linear correlation approximately. By fitting the errors, the total internal partition functions values at high temperature range of 3000 K to 6000 K were corrected. The corrected total internal partition functions are fitted to a four-order polynomial expression in T, and the coefficients are gained at high temperature. This allows a rapid and accurate calculation of the total internal partition functions at the temperature from 3000 K to 6000 K.