  Excited-state vibrational dynamics in molecules can be studied by an
electronically off-resonant Raman process induced by a probe pulse with
variable delay with respect to an actinic pulse. We establish the connection
between several variants of the technique that involve either spontaneous or
stimulated Raman detection and different pulse configurations. By using loop
diagrams in the frequency domain we show that all signals can be described as
six wave mixing which depend on the same four point molecular correlation
functions involving two transition dipoles and two polarizabilities and
accompanied by a different gating. Simulations for the stochastic
two-state-jump model illustrate the origin of the absorptive and dispersive
features observed experimentally.
