  Electron and vibrational dynamics of molecules are commonly studied by
subjecting them to two interactions with a fast actinic pulse that prepares
them in a nonstationary state and after a variable delay period $T$, probing
them with a Raman process induced by a combination of a broadband and a
narrowband pulse. This technique known as femtosecond stimulated Raman
spectroscopy (FSRS) can effectively probe time resolved vibrational resonances.
We show how FSRS signals can be modeled and interpreted using the stochastic
Liouville equations (SLE) originally developed for NMR lineshapes. The SLE
provides a convenient simulation protocol that can describe complex dynamics
due to coupling to collective coordinates at much lower cost that a full
dynamical simulation. The origin of the dispersive features which appear when
there is no separation of timescales between vibrational variations and
dephasing is clarified.
