Calculations of thermodynamic sulfur isotope effect.

Abstract

The isotopic reduced partition function ratios (RPFR), (s/s')f, for the 34S/32S isotopic pair were calculated for 24 sulfur compounds between 10 and 2,000K. Their magnitudes were in the following sequences; at low enough temperatures at which In(s/s')f depends only on the isotopic difference in frequency-sum, SF6>SO2F2>SF5Cl>SF5Br>SO4 2->SO2Cl2>SO3>NSF3>SF4>SOF2>SOCl2>Me2SO>SOBr2>SO2>SPBr3>SCBr2>Me2S>SPCl3>SCCl2>SCF2>SPF3>CS2>OCS>H2S, and at high enough temperatures at which In(s/s')f is proportional to the isotopic difference in the sum of frequencies squared, SO2F2>SO4 2->SO3>SF6>SO2Cl2>SF5C1>NSF3>SF5Br>SOF2>SO2>SF4>Me2SO>SCCl2>SOBr2>H2S>Me2S>CS2>SCF2>OCS SCBr2>SPF3>SPCl3>SPBr3 where Me--CH3. Correlation of the RPFR with molecular structure and molecular forces was discussed. The equilibrium constants K for the 34S/32S isotope exchange reactions of all the possible pairs of 19 sulfur compounds selected out of the above 24 were calculated and their temperature dependences were investigated. Two typ...