Abstract
In the spirit of Blaise et al.'s work [P. Blaise et al, J. Chem. Phys. 122 (2005) 64306], we have extended their approach by accounting for the anharmonicity of the slow mode which is described by a "Morse" potential in order to reproduce the unpolarized VX-H infrared lineshapes of cyclic acetylsalicylic acid (aspirin) and its OD derivative at 300 K and 77 K
The simulation takes into account (i) the anharmonic, coupling between the high frequency mode and the H-bond bridge, (ii) the Davydov coupling between the excited states of the two moieties, (iii) the quantum direct and indirect dampings, (iv) the arharmonicity for the H-bond bridge,
We have obtained the spectral density (SD) within the linear response theory by Fourier transform of the damped autocorrelation functions. The evaluated spectra are in fairly good agreement with the experimental ones. The effect of deuteration has been well reproduced by this approach. Our results show that spectra of aspirin and its deuterated analog can be successfully reproduced by using a minimum number of independent parameters.