ASSIGNING STATES IN THE JAHN-TELLER COUPLED INFRARED SPECTRA OF CH3O AND CD3O

The ground X̃E vibrations of the methoxy radical have intrigued both experimentalists and theorists alike due to the presence of a conical intersection at the C3v molecular geometry. This conical intersection causes methoxy’s vibrational spectrum to be strongly influenced by Jahn-Teller coupling, this leading to large amplitude vibrations and extensive mixing of the two lowest electronic states. This coupling combined with spin-orbit and Fermi couplings greatly complicates the assignments of states. In this talk we describe our efforts to assign the states of both CH3O and CD3O. Using the potential energy force field and calculated spectra of Nagesh and Sibert as a starting point, vibrational mixing is considered using various zero-order representations. When the zero-order states are the diabatic normal mode states, there is sufficient mode mixing that the normal mode quantum numbers are no longer good labels. The mixing of the zero-order states can be reduced by including additional terms in the zero-order Hamiltonian, H. We consider the choice of including the first order Jahn-Teller coupling between one of the three degenerate normal modes. As the rocking motion has the largest Jahn-Teller coupling, this is the coupling that is included in H. Although the normal mode quantum numbers of the rocking basis functions are no longer good quantum numbers, due to the Jahn-Teller induced vibronic mixing, the zero-order states can be labeled with the linear Jahn-Teller quantum numbers. This work extends these ideas by considering an H that includes linear Jahn-Teller coupling between two sets of degenerate vibrations. Plots of the resulting zero-order states are presented, and the spectral transitions recently observed for both CH3O and CD3O in a p-H2 matrix are assigned using these basis functions. The extent of state-mixing found for the full Hamiltonian H for various choices of H is illustrated via the use of correlation diagrams obtained by plotting the eigenvalues of H + δ(H − H) as a function of δ where δ varies from zero to one.