Excited-state (ES) potential energy surfaces (PESs) govern ultrafast light-activated reactions. Conventional spectroscopy only reveals the absolute value of ES displacements, not their direction. This paper introduces a two-color broadband impulsive Raman experimental scheme to directly measure complex Raman excitation profiles, revealing the magnitude and direction of ES displacements relative to the ground state. This is achieved through non-degenerate resonant probe and off-resonant pump pulses, providing time-domain sensitivity to the phase of stimulated vibrational coherences.

Giovanni Batignani, Emanuele Mai, Giuseppe Fumero, Shaul Mukamel, Tullio Scopigno