Vibrational dynamics around the conical intersection: a study of methoxy vibrations on the (X)over-tilde(2)E surface

The large-amplitude vibrational dynamics of methoxy (CH3O), resulting from the conical intersection at the C-3v geometry, are investigated using variational methods. A two-dimensional model Hamiltonian consisting of two vibrational degrees of freedom and the coupling between them is presented in a diabatic representation of the electronic degrees of freedom. The observed complex dynamics are understood in terms of the multiple timescales that arise as the initial wave packet passes through the conical intersection. This model Hamiltonian is extended to include a full-dimensional treatment of methoxy. A quartic potential is calculated using both single and multiple configuration methods. The vibronic eigenstates are calculated using a series of basis set contraction schemes taking a primitive basis of harmonic oscillator wave functions as the starting point. Our final results, including spin-orbit coupling, are compared to experiment.