The incoherent dynamic structure factor of orthoterphenyl is studied by quasielastic neutron scattering to 240 MPa. Tagged-particle correlations in the compressed liquid decay in two steps. The α-relaxation line shape is independent of pressure, and the relaxation time proportional to viscosity. A kink in the amplitude fQ(P) reveals the onset of β relaxation. The β-relaxation regime can be described by the mode-coupling scaling function; amplitudes and time scales allow a consistent determination of the critical pressure Pc(T). α and β relaxation depend in the same way on the thermodynamic state; close to Pc(T), this dependence can be parametrized by an effective coupling Γ∝nT^-1/4.
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Tölle et al. (1998) studied this question.
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