Microscopic dynamics of hard ellipsoids in their liquid and glassy phase

To investigate the influence of orientational degrees of freedom onto the dynamics of molecular systems in its supercooled and glassy regime we have solved numerically the mode-coupling equations for hard ellipsoids of revolution. For a wide range of volume fractions $ϕ$ and aspect ratios $x₀$ we find an orientational peak in the center of mass spectra $χ₀₀₀^''(q,ω)$ and $ϕ₀₀₀^'' (q,ω)$ about one decade below a high frequency peak. This orientational peak is the counterpart of a peak appearing in the quadrupolar spectra $χ_22m^''(q,ω)$ and $ϕ_22m^''(q,ω)$. The latter peak is almost insensitive on $ϕ$ for $x₀$ close to one, i.e. for weak steric hindrance, and broadens strongly with increasing $x₀$. Deep in the glass we find an additional peak between the orientational and the high frequency peak. We have evidence that this intermediate peak is the result of a coupling between modes with $l=0$ and $l=2$, due to the nondiagonality of the static correlators.