Abstract
The influence of electrical anharmonicity on the infrared shape of the D(5)(X - (H) over right arrow...Y) stretching vibrations is investigated. For this aim, we extend a previous approach [Rekik et al., Chem. Phys. 352 (2008) 65-76] by accounting for variable dipole moment. The approach is involving anharmonic coupling between the high frequency stretching vibration, X - (H) over right arrow...Y (double well potential) and low-frequency donor-acceptor stretching mode (X) over left arrow - H...(Y) over right arrow (Morse potential), Fermi resonances between states involving the X - (H) over right arrow...Y stretching and overtones or combinations of some internal modes, as well as the electrical anharmonicity of dipole moment operator of the fast mode. Direct relaxation mechanism is incorporated through a time decaying exponential according to Rosch and Ratner theory. The approach has been constructed in the framework of the linear response theory for which spectral density is obtained by Fourier transform of the autocorrelation function of the dipole moment operator of the fast mode.
It follows from numerical results that electrical anharmonicity has a very substantial effect on the intensity of the hydrogen-bonded stretching vibration and provide explanation of the most important intensity changes that occur upon hydrogen bond formation. (c) 2010 Elsevier B.V. All rights reserved.