Structure and vibrations of catechol in the S1 state and ionic ground state

To determine structure and vibrations of catechol and d2-catechol (C6H4(OD)2) in the ionic ground state, MATI spectra as well as ab initio and DFT calculations are presented. The comparison of the experimentally observed vibrational frequencies with the calculated values leads to a complete assignment of all vibrations. CASSCF and DFT calculations predict a planar geometry of catechol in the S0 and D0 states. CASSCF calculations for the S1 state show that the free OH group of catechol is rotated out of the plane of the aromatic ring by ∼24°. This calculation supports the assumptions of earlier experimental work. The adiabatic excitation energies (S1←S0) and the adiabatic ionization potentials of catechol and its deuterated isotopomer can be predicted by CASSCF calculations including zero-point energies and MP2 corrections.