Najeh Rekik

A full quantum theoretical model is proposed to study the nu(O-H) experimental IR line shapes of polarized crystalline glutaric and 1-naphthoic acid dimer crystals at room and liquid nitrogen temperatures. This work is an application of a previous model [M. E-A. Benmalti, D. Chamma, P. Blaise, and O. Henri-Rousseau, J. Mol. Struct. 785 (2006) 27-31] by accounting for Fermi resonances. The approach is dealing with the strong anharmonic coupling, Davydov coupling, multiple Fermi resonances between the first harmonics of some bending modes and the first excited state of the symmetric combination of the two nu(O-H) modes and the quantum direct and indirect relaxation. Numerical results show that mixing of all these effects allows to reproduce satisfactorily the main features of the experimental IR line shapes of crystalline hydrogenated and deuterated glutaric and 1-naphthoic acid crystals and are expected to provide efficient of Fermi resonances effects.

The bandshape of hydrogen bond vibrations in liquids is studied theoretically, taking into account the anharmonic coupling between the high-frequency stretching vibration, X−H→…Y (double well potential), and low-frequency lattice phonons, X←−H…Y→ (Morse potential), as well as Fermi resonances between states involving the X−H→…Y stretching and overtones or combinations of some internal modes. The relaxation of the fast mode (direct damping) and of the H-bond bridge (indirect damping) is incorporated by aid of previous results [N. Rekik, B.Ouari, P. Blaise, O. H. Rousseau, J. Mol. Struct. (Theochem) 687 (2004) 125–133]. 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. Numerical results show that mixing of all these effects results in a broad and complicated structure. The indirect damping favourites have a more sensitive smoothing of the full line shapes whereas the direct one entrains a broadening of the spectra.

The influence of electrical anharmonicity on the infrared shape of the υS(X-H→…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→…Y (double well potential) and low-frequency donor–acceptor stretching mode X←-H…Y→

The paper presents extension of a quantum non-adiabatic treatment of H-bonds in which effects of anharmonicities of the high frequency XH→⋯Y and the low frequency X←H⋯Y→ modes on the υX–H infrared lineshapes of H-bonds systems are considered. The anharmonic coupling between the high frequency XH→⋯Y and the low frequency X←H⋯Y→ modes is treated within strong anharmonic coupling theory and the

Anomalous isotopic effects on the position and the shape of the υs(X–H→…Y) stretching vibration bond of hydrogen-bonded systems have been studied theoretically by applying a previous model [N. Rekik, N. Issaoui, H. Ghalla, B. Oujia, M.J. Wojcik, J. Mol. Struct. (Theochem) 821 (2007) 9–29]. The study of this effect is undertaken for weak to medium-strong H-bonded systems. Numerical results show

We extend a quantum nonadiabatic treatment of damped H-bonds involving combined effects of anharmonicities of both the fast and the slow modes, Fermi resonances and relaxation [Rekik et al., J Mol Liq (in press)] in order to account for stronger H-bonds. For this purpose, we introduce, in the model, the quadratic modulation of both the angular frequency and the equilibrium position of the X − …Y stretching mode on the intermonomer motions to refine the structure of the spectrum, whereas we have considered in our previous work only the linear modulation of the angular frequency of the fast mode. In this approach, the strong anharmonic coupling theory is used through second-order expansion in the slow-mode coordinate Q of the angular frequency and the equilibrium position of the fast mode. The relaxations of the fast mode (direct damping) and of the H-bond bridge (indirect damping) are incorporated by aid of previous results [Rekik et al., J Mol Struct 2004, 687, 125]. The spectral density is obtained by Fourier transform of the autocorrelation function of the dipole moment of the fast stretching mode. The numerical calculation shows that the modulation of the angular frequency of the fast mode and its equilibrium position by the slow mode coordinate generate an improvement of the fine structure of the spectrum and also provide a direct evidence of the increase of the level density and the spectral broadening. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009

The IR spectral density (SD) of the high frequency stretching mode of H-bonded complexes involving both the intrinsic anharmonicity of the fast and slow mode, together with direct and indirect relaxations is studied within the linear response theory. For this aim, we extend a quantum non-adiabatic treatment of H-bonds involving intrinsic anharmonicity of the fast mode [N. Rekik, A. Velescu,

In this article, we extend a previous work toward presenting a theoretical study of the effects of Fermi resonances and the fundamental anharmonic coupling parameter α between the high-frequency mode and the H-bond bridge. The model incorporates (i) both intrinsic anharmonicities of the fast mode (double well potential) and the H-bond Bridge (Morse potential), (ii) strong anharmonic coupling theory, (iii) Fermi resonances by the aid of an anharmonic coupling between the fast mode and one or several harmonic bending modes, (iv) quadratic modulation of both the angular frequency and the equilibrium position of the X…Y stretching mode on the intermonomer H… motions, and (v) the quantum direct (fast and bending modes) and indirect dampings (slow mode). The IR spectral density is obtained by Fourier transform of the autocorrelation function of the transition dipole moment operator of the XH bond. The numerical calculation shows that Fermi resonances generate very complicated profiles with multisubstructure and also provide a direct evidence of Fermi resonances which were predicted to be a major feature of H-bonds. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010

The paper presents extension of a quantum non-adiabatic treatment of H-bonds involving intrinsic anharmonicity of the fast mode [Rekik et al. Chem. Phys. 273 (2001) 11] by accounting for quadratic dependence of both the angular frequency and the equilibrium position of the XH→⋯Y stretching mode on the X←H⋯Y→ motion, in order to account for stronger H-bonds. Attention is focused on