Abstract
In this paper, we present the results of isotopic effect resulting from a more general quantum approach of the nu(X-H) IR lineshape, aiming to explain the evolution of this effect when one passes from weak to medium strong hydrogen bond systems. The approach, using both intrinsic anharmonicity of the fast mode and the H-bond Bridge, is dealing with the linear response theory and within the framework of strong anharmonic coupling theory. The direct damping is introduced in a phenomenological way as in the very fundamental model of Rosch and Ratner.
The numerical results show a continuity of the isotopic effect when one passes from the range of weak H-bonds to the range of medium strong H-bonds. This was elucidated by studing the evolution of the ratio r= (H)/ (D), the half-widths Delta omega(H) - Delta omega(D) as well as (H) - (D).
Besides, the result leads to conclude that the isotopic effects resulting from the Rosch and Ratner model in weak hydrogen bonds may be partially transposed beyond the harmonic approximation for the slow and fast mode.