Beyond the harmonic approximation in the theoretical study of flexible molecules. Application to chemical reactions and tunneling splittings

Abstract

During this project a new theoretical method will be developedin order to obtain accurate partition functions for molecular systems that present two internal rotations.Such method will be applied to a bunch of different molecules and the results will be thoroughly analyzed and compared with those obtained with the other methods available such as Pitzer-Gwinn, Ayala-Schlegel or Chuang-Truhlar. The convenience of the application of the different methods (one dimensional methods will also be included) in relation with the nature of the molecule considered will be widely discussed throughout this work. Moreover, a qualitative and quantitative interpretation of the tunneling splitting phenomena present for some molecules will be offered, bringing some insight for an adequate understanding of the results found in practice. Finally, a kinetic study for a reaction that involves an hydrogen abstraction will be carried out, for doing this we will use the transition state theory considering variational effects, tunneling effects and the different possible reaction paths. The anharmonicity due to the torsional motion will also be included.