Effects of intense femtosecond pumping on ultrafast electronic-vibrational dynamics in molecular systems with relaxation.

We investigate the influence of strong femtosecond optical pulses on the ultrafast dynamics of molecular systems. The study is based on a series of generic molecular models of increasing complexity, which incorporate multiple and mutually coupled electronic states, electronic-vibrational interaction, and vibrational relaxation. The influence of vibrational relaxation is treated using multilevel Redfield theory. Comparisons to benchmark results of the multilayer multiconfiguration time-dependent Hartree (ML-MCTDH) method demonstrate the validity of the field-free implementation of Redfield theory employed in this work for weak system-bath interaction. The calculated electronic population and vibrational wave-packet dynamics demonstrate the intricate interplay of strong-field excitation, laser-induced Rabi oscillations, electronic interaction, vibronic coupling, and dissipation. In particular, we show that the interaction with a strong laser pulse may result in pronounced coherent vibrational motion in a dissipative system, even for laser pulses that are longer than the vibrational period. Furthermore, vibrational relaxation in combination with strong laser pulse excitation can lead to revivals of the electronic population after the excitation pulse is over.