Fifth-order Raman spectrum of an atomic liquid: Simulation and instantaneous-normal-mode calculation

Experimental artifacts and technical difficulties in carrying out theoretic al calculations have consistently frustrated attempts to obtain the two-dim ensional (5th-order) Raman spectrum of a liquid. We report here a new theor etical development: the first microscopic numerical simulation of the 5th-o rder Raman signal in a liquid. Comparison with an instantaneous-normal-mode treatment, a fully microscopic model which interprets liquid dynamics as a rising from coherent harmonic modes, shows that the 5th-order spectrum reve als profound effects stemming from dynamical anharmonicity.