Ab initio investigation of the H2O2 + F elementary reaction

Abstract

Elementary gas phase reaction of hydrogen peroxide with fluorine atom has been investigated theoretically using ab initio quantum chemistry methods. Two possible reaction paths are considered: the H-abstraction path leading to HO2 and HF products and the OH-abstraction one leading to OH and HOF products. The optimized structures and the harmonic vibrational frequencies of all the stationary points are calculated using the electronic structure CCSD(T) method with the jun-cc-pVTZ basis set. The influence of the basis set is analyzed by performing single point CCSD(T) energy calculations using the jun-cc-pVQZ and aug-cc-pVTZ basis sets. For the H-abstraction path, the reaction is found to be barrierless. The ZPE corrected CCSD(T)/jun-cc-pVTZ, CCSD(T)/jun-cc-pVQZ//CCSD(T)/jun-cc-pVTZ and CCSD(T)/aug-cc-pVTZ//CCSD(T)/jun-cc-pVTZ classical barrier heights are predicted to be −2.5, −3.0 and −3.1kcalmol−1, respectively. A reactant complex (RC) is located at the entrance channel with a relative stability about 1.3kcalmol−1 compared to the transition state. These results suggest that the reaction according to this path is very fast, which can explain the remarkable lack of kinetic experimental observations. For the OH-abstraction path, the CCSD(T)/jun-cc-pVTZ, CCSD(T)/jun-cc-pVQZ//CCSD(T)/jun-cc-pVTZ and CCSD(T)/aug-cc-pVTZ//CCSD(T)/jun-cc-pVTZ barrier heights including ZPE correction are found to be 14.6, 14.0 and 13.3kcalmol−1. This latter value is used to evaluate the thermal rate constants kTST by means of the transition state theory TST over the temperature range of 200–2500K. The resulting values of kTST show that this path has no significant contribution to the title reaction.