IR spectral density of weak H-bonds involving quantum direct and indirect dampings. Beyond the adiabatic and harmonic approximations

In the framework of our full quantum approach of damped weak hydrogen bonded system infrared spectra [Adv. Chem. Phys. 103 (1998) 1], we have explored two new ways of introducing the direct and indirect relaxations of the nX–H high frequency stretching mode toward the medium considered as a thermal bath. In continuity with a preceding paper [Chem. Phys., in press], we take into account the relaxation by introduction of imaginary parts reflecting the damping process, in the quantum energy levels of the undamped Hamiltonians. This method allows treating situations lying beyond the adiabatic approximation that was not possible in the precedent approaches. q 2003 Elsevier B.V. All rights reserved.