  In most cases the ultrafast dynamics of resonantly excited molecules are
considered, and almost always computed in the molecular frame, while
experiments are carried out in the laboratory frame. Here we provide a
formalism in terms of a lab frame density matrix which connects quantum
dynamics in the molecular frame to those in the laboratory frame, providing a
transparent link between computation and measurement. The formalism reveals
that in any such experiment, the molecular frame dynamics vary for molecules in
different orientations and that certain coherences which are potentially
experimentally accessible are rejected by the orientation-averaged reduced
vibronic density matrix. Instead, Molecular Angular Distribution Moments
(MADMs) are introduced as a more accurate representation of experimentally
accessible information. Furthermore, the formalism provides a clear definition
of a molecular frame quantum tomography, and specifies the requirements to
perform such a measurement enabling the experimental imaging of molecular frame
vibronic dynamics. Successful completion of such a measurement fully
characterizes the molecular frame quantum dynamics for a molecule at any
orientation in the laboratory frame.
