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CASSCF/CASPT2 study of mechanism and kinetics of the gas-phase ozone additions to ethene, fluoroethene and chloroethene

A comprehensive CASSCF/CASPT2 study into the reaction mechanism and kinetics of the gas-phase ozone addition to ethene, fluoroethene and chloroethene is presented. All of the molecular species along the three complex reaction paths were optimized at the multicofigurational CASSCF/cc-pVTZ level, always utilizing the appropriate flexible enough active spaces. The calculated electronic energies were further refined at the multireferent CASPT2/cc-pVTZ level with the optimized CASSCF wave functions taken as the zeroth order. The Arrhenius kinetic parameters calculated in terms of the conventional transition state theory are in a very good agreement with the experimental parameters. On basis of these studies, as well as the CASPT2 study of the ground state equlibrium geometry, harmonic frequencies and anharmonic force field of the ozone molecule, it is shown that the performance of the relatively inexpensive CASSCF/CASPT2 treatment is entirely comparable to some much more demanding treatments which had been used previously in studying ozone and ozonolyses.

quantum chemistry; CASSCF; CASPT2; multireference methods; ozone; ethene; fluoroethene; chloroethene; mechanism; kinetics

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