Fifth-Order Raman Spectrum of an Atomic Liquid: Simulation and Instantaneous-Normal-Mode Calculation

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