A kinetic investigation of unimolecular reactions involving trace metals at post-combustion flue gas conditions

Ab-initio methods were carried out to calculate forward and reverse rate constant data for the following reactions: HgþCl22HgCl2, HgClþCl2HgCl2, HgþO2HgO, and SeþH22SeH2. Theoretical predictions of bond distances, vibrational frequencies and enthalpies of reaction are compared to available experimental data to determine the level of theory most appropriate for predicting kinetic parameters. The pseudopotentials ECP60MDF and RECP60VDZ were used for mercury in combination with B3LYP or QCISD(T) methods whereas the complete 6–311þþG(3df,3pd) Pople basis set with the CCSD(T) method was used for selenium. Potential energy curves for each reaction were constructed and a variational approach along with RRKM theory was used to predict rate constants from 298 to 2000K. Reactions HgClþCl2HgCl2 and HgþO2HgO were found to have a strong negative temperature dependence, whereas the insertion reactions HgþCl22HgCl2 and SeþH22SeH2 were found to proceed very slowly with large pre-exponential factors.