Visualization of dissipative wavepacket dynamics at conical intersections

The effect of a dissipative thermal environment on the ultrafast nonadiabatic dynamics at conical intersections is nowadays well understood. Yet, the molecular wavepacket dynamics at conical intersections has not been directly characterized and monitored via femtosecond nonlinear spectroscopy. Transient absorption pump-probe spectroscopy with white-light continuum detection has recently reached a 5-10 fs time resolution, which enables a direct characterization of molecular wavepackets possessing multiple vibrational modes. We have combined the hierarchy equation of motion with the equation-of-motion phase-matching approach to simulate pump-probe and fluorescence up-conversion signals for a model of S₂(ππ*)-S₁ (nπ*) conical intersection in pyrazine which is bilinearly coupled to a harmonic bath with Drude spectral density function. Our results show that the signals indeed visualize evolutions of the wave packet at conical intersections, and these evolutions are quite sensitive to the bath parameters as well as to the envelope of the laser pulses.