HIGHER VIBRATIONAL-STATES OF OH/OD IN THE BULK OF CONGRUENT LINBO3 AND IN PROTON DEUTERON EXCHANGED LAYERS AT THE SURFACE OF LINBO3

The fundamental vibrational transition <(nu)over bar>(01) and the higher vibrational transitions <(nu)over bar>02, <(nu)over bar>(03) and <(nu)over bar>(04) of the OH and the OD oscillator in the bulk of congruent LiNbO3 and in proton/deuteron exchanged LiNbO3:PE/DE surface layers are investigated with respect to their spectroscopic properties and their temperature dependence. All observed vibrational transitions are completely polarized perpendicular with respect to the ferroelectric z direction. The spectral positions of the vibrational transitions follow closely a Morse type potential with D-e = 4.75 eV and a = 22.23 nm(-1) (omega(e,OH) = 3684 cm(-1) and omega(e)x(e,OH) = 88.5 cm(-1) for LiNbO3:PE). No hint of possible hydrogen bonding was found. The integrated absorption intensity ratios of the higher vibrational transitions exhibit the existence of an electrical anharmonicity, i.e. a non-linearity of the dipole moment versus O-H separation. The electrical anharmonicity reveals a noticeable temperature dependence whereas the vibrational transition energies and therefore the mechanical anharmonicity shows no temperature dependence in the range from room temperature to liquid helium temperature.