A local mode analysis of the stretching mode spectra of liquid H 2O and D 2O in the temperature range 4 ⪢2- 200 °C

Abstract

A harmonically coupled non-symmetric (r 1 ≠ r 2) anharmonic oscillator model has been used to compute the stretching mode spectra of liquid H 2O and D 2O. The effect of anharmonicity, intra- and intermolecular coupling on the band shape has been investigated by using only the two stretching coordinates. Molecular interaction are described by the Lippincott-Schroeder potential function for bent hydrogen bonded systems. A quantum local mode analysis of the random molecule configurations is used to compute the eigenstates. Local mode behaviour and oscillator non-similarity produced decoupling for H 2O the latter manifesting itself in the appearance of a high frequency shoulder at 4 °C and at 50 °C. In contrast the normal mode picture of D 2O causes a high frequency splitting at 150 °C and 200 °C beacuse of coupling between similar oscillators.