Polarizability response in polar solvents: Molecular-dynamics simulations of acetonitrile and chloroform

Abstract

The relaxation of the many-body polarizability in liquid acetonitrile and chloroform at room temperature was studied by molecular-dynamics simulations. The collective polarizability induced by intermolecular interactions was included using first- and all-orders dipole-induced-dipole models and calculated considering both molecule-centered and distributed site polarizabilities. The anisotropic response was analyzed using a separation scheme that allows a decomposition of the total response in terms of orientational and collision-induced effects. We found the method effective in approximately separating the contributions of these relaxation mechanisms, although the orientational-collision-induced interference makes a non-negligible contribution to the total response. In both liquids the main contribution to the anisotropic response is due to orientational dynamics, but intermolecular collision-induced (or translational) effects are important, especially at short times. We found that higher-order interaction-induced effects were essentially negligible for both liquids. Larger differences were found between the center-center and site-site models, with the latter showing faster polarizability relaxation and better agreement with experiment. Isotropic and anisotropic spectra were computed from the corresponding time correlation functions. The lowest-frequency contributions are largely suppressed in the isotropic spectra and their overall shape is similar to the purely collision-induced contribution to the anisotropic spectra, but with an amplitude which is smaller by a factor of approximately 5 in acetonitrile and approximately 3 in chloroform.

Ion effect on the dynamics of water hydrogen bonding network: A theoretical and computational spectroscopy point of view

“…The time correlation functions of the cross terms have similar time dependence with the reorientation part if there exist clear time scale separations and the reorientation component is much slower than the collision-induced component. These time correlation functions are usually negative, which makes the contribution of reorientation terms smaller and the contribution of collision-induced terms larger (Elola & Ladanyi, 2005;Ladanyi & Liang, 1995). For methanol and water, the cross terms appear to be positive (Ladanyi & Liang, 1995;Sonoda, Vechi, & Skaf, 2005).…”

Dielectric response and collective dynamics of acetonitrile

“…2). This is expected as molecular inertia, caging (dipole libration) and interaction-induced effects are dominating the terahertz region [5,[37][38][39]. As discussed in detail below, the dominating peak in the dielectric loss spectrum, ε′′(ν), at~40 GHz (1 in Fig.…”

“…(3), is associated with the rotational diffusion of the AN dipoles. The assignment of the G mode (3), giving rise to the peak in the absorption coefficient, α, at~90 cm −1 , to libration is also straightforward [5,15,37,38].…”

Modeling the low frequency vibrational spectroscopy of ionic solutions

“…For the TCFs of the cross terms, they should have similar time dependence with the reorientation part if there exists clear time scale separations and the reorientational component is much slower than the collision‐induced component. The TCFs of the cross terms are usually negative, which makes the contribution of reorientation become smaller and that of collision‐induced larger . For methanol and water, the cross terms appear to be positive .…”